Final Report Summary - MESO (Meso-superstructured Hybrid Solar Cells)
Executive Summary:
In this project we developed a new class of low cost solution processible hybrid solar cells based on metal halide perovskite absorbers and organic or metal oxide charge collection layers. This “heterojunction” solar cell technology proved to be remarkably efficient on its first reduction to practice, and over the course of the project has now shown tremendous scope to compete with the very best crystalline semiconductor and thin film technologies on efficiency, while offering the very lowest potential cost for materials and solution processed manufacturing. On the granting of MESO, our targeted end of project efficiency for single junction perovskite solar cells was “an ambitious” 16%. However, the technical progress over the course of the project has been unexpectedly rapid, and this target has been smashed, with us having presented devices delivering over 21% power conversion efficiency. The activities in MESO have spanned from synthesis of new organic-inorganic perovskite absorbers and organic hole-conductors, theoretical modelling, through thin film deposition and integration, device optimization, characterisation and advanced spectroscopy, to scale-up, stability enhancement and certification and demonstrator mini-module manufacture. Our consortium consists of leading academics in Europe; pioneers of hybrid solar cells, expert organic and inorganic synthetic capabilities, leaders in electronic energy level calculations, interfaces and device simulation, world class advanced spectroscopy, and a dynamic early stage technology company. This diverse yet perfectly complementary pan European consortium ensured that the MESO project delivered on its objectives, and is on track to realize a new commercial photovoltaic technology. Our achieved objectives have been to realise extremely efficient single junction perovskite solar cells, tandem perovskite solar cells by combining perovskite with silicon technologies and all perovskite tandem solar cells. Beyond efficiency, a key target has been to enable the perovskite technology to surpass the international standard thin film solar cell environmental stressing certification, IEC61646, and the perovskite-on-silicon tandem cells have surpassed both thermal cycling and damp heat IEC tests, in addition to 1000hrs full sun light soaking at 60C with less than 5% relative degradation in performance. This is a key milestone which has enabled the perovskite technology to move towards the next stage in the path towards industrialisation.
Project Context and Objectives:
This project brings together the leading research groups and industry in Europe investigating, developing and commercialising solid-state hybrid solar cells. The ambitious “concept” of the project is to take the perovskite based meso-superstructured solar cell from its first introduction to commercial launch within the 3 year project timeframe. This will be achieved by; i) developing new, ideally optimised materials (both organic hole-conductors and perovskite absorbers) delivering improved performance and stability; ii) optimising the processing and integration of these materials into manufacturable high efficiency devices and modules; iii) probing and understanding the fundamental processes occurring in the materials and operational solar cells to give a rational approach to the design and implementation of new materials. MESO is broken down into 5 RTD work packages (WPs), 1. Material Synthesis and characterisation, 2. Device Integration and testing, 3. Fundamental Investigations and modelling, 4. Scale-up, and 5. Stability enhancement, with an additional Demonstrator WP6. For each WP there is one or two key Objectives (O):
O1 Creation of a perovskite absorber with optimum bandgap for maximum efficiency and enhanced stability. (WP1) We will employ a combinatorial approach to screen perovskite structures and develop a library of materials with a range of electronic and optical properties. The starting choices will largely be based on available literature on perovskites, however, new material families will also be computationally screened to predict their electronic and optical properties. The key challenges are: 1. Tune the band gap: To move the absorption onset out to 940nm (1.3eV) for the single junction solar cells, and to 730nm (1.7eV) and 1100nm (1.1eV) onset for optimum absorbers in a tandem junctions. 2. Enhance the stability: Reduced moisture and oxygen sensitivity will be achieved by employing non-hygroscopic cationic organic ligands and tuning the inorganic metal cations and halide or chalcogenide anions. 3. Optimise the level of doping: In addition to having the ideal band gap and stability, since the perovskite functions as both the absorber and n-type charge transporter in the MSSC, it is essential that its level of doping is optimised. This will be achieved by using mixed anions and doping with different metal cations. This objective relates to innovative materials, improved stability and better control of the band-gap addressed by the call.
O2 Conceive and create an advanced organic hole-conductor with superior performance and stability in MSSCs. (WP1) We will undertake a synthetic strategy to develop a new family of hole-conducting molecules, and oligomers to polymers which have high mobility and tuneable highest occupied molecular orbitals (HOMOs) to maximise hole-transfer efficiency, and open-circuit voltage, while minimising series resistance and recombination losses. We will also address thermal and UV-stability issues to enable long term performance. Ab initio computer simulations will assist the design of new materials with target electronic and optical properties. This relates to novel organic semiconductors with an improved thermal and photochemical stability in combination with a higher power conversion efficiency addressed by the call.
O3 Realise an optimum low temperature processed scaffold for MSSCs (WP1/ WP2) will be achieved by finding the optimum porosity, meso-scale and material type for the mesoporous scaffold (WP1). Subsequent device optimisation with the low temperature paste will lead to a successful outcome (WP2). This relates to advances in non-vacuum coating and printing techniques, and in addition to enabling tandem cell construction as targeted in this project, it will enable flexibility and economically interesting processing technologies, as addressed in the call.
O4 Realise an optimum glass coated TCO/n-type collection layer for MSSCs. (WP1/ WP2/ WP5/ WP6) will be achieved by developing higher transparency, lower sheet resistivity coated glass than FTO. This Objective is especially relevant to the scale up and demonstrator activities in WP4 and WP6.
O5 Tandem tunnel junction realise a processible highly transparent, low resistance tunnel-junction for multi-junction MSSCs.(WP1/WP2/WP5)
O6 Demonstration of an MSSC single junction solar cell with greater than 16% efficiency (WP2) will be achieved by combing the new materials developed in WP1, with optimised processing, including variations in, alumina scaffold film thickness, perovskite and hole-transporter concentrations and coating conditions, level of doping in the perovskite and hole-conductor, perovskite drying temperature and time etc..
O7 Demonstration of a 21% efficient hybrid tandem-junction MSSC on c-Si (WP2). To kick start the tandem activity and enable broader adoption of the MSSC across the PV community it is an objective to demonstrate enhanced c-Si solar cell efficiency by combining with our baseline MSSC as a two terminal monolithic hybrid tandem solar. This relates to better cost/efficiency ratio as compared to conventional PV.
O8 Demonstration of a 19% efficient tandem-junction MSSC (WP2). Realising a low temperature route to the MSSC opens up the possibility of monolithic tandem solar cells. We will follow the route tried and tested in OPV of using a conducting p-type polymer (PEDOT:PSS) and n-type metal oxide (TiO2 or ZnO) as the tunnel junction. The device architecture will consist of a wide gap front cell (1.7eV band gap) coated with PEDOT:PSS/TiO2 (or ZnO) tunnel junction with a narrow gap rear cell. O4 and O5 relate to a higher power conversion efficiency and production of (certified) reference materials addressed from the call
O9 Full understanding of the operation of the solar cell and performance limiting factors. (WP3) By combining a broad range of advanced optical spectroscopy and electronic characterisation tools, along-side first principle materials and device modelling, we will develop a comprehensive understanding of the fundamental optical and electronic processes occurring in the materials and the operation of the complete devices. This knowledge will be invaluable to help redirect the materials synthesis and device engineering efforts throughout the project. This relates to, a better understanding of the long term stable operation and the degradation mechanisms at the material level, addressed by the call.
O10 Demonstration of certifiable solar cell stability. (WP5) There is no certain means to ensure a solar technology will last for 25 years, without having it in the filed for 25 years. However, since this is infeasible in the timeframe of product development to market, and indeed in the timeframe of this project, accelerated testing will be employed. We will age the solar cells at 85°C under simulated full sun illumination with the target of achieving less than 20% drop in performance after 1000hrs illumination. 25 years is approximately 54,750 hrs full sun illumination, assuming the equivalent of 6 hrs full sun light/day, or 250Wm 2 average irradiance (equivalent to North Africa). Taking a standard acceleration factor of 2 for each ten degrees increase in temperature, an acceleration factor of 64 is estimated for 85 °C as opposed to 25 °C degrees, and hence the 54,750 hrs equivalent would be reached before 1000 hrs. However, although this will give confidence, the standard solar cell accreditation requires a series of stress tests including temperature cycling and damp heat. We will stress our cells to 5 of the most critical tests in the IEC61646 thin film standard certification internally, and identify and eradicate failure mechanisms. A set of 8 modules will then be subject to IEC61646 at an accredited test facility. It is an objective that they pass this test. This relates to a better understanding of the long term stable operation and the degradation mechanisms at the material level can contribute to increasing the lifetime of the cells, which should be targeted, and production of (certified) reference materials addressed by the call.
O11 The scale-up of the processing to minimodule and the creation of a demonstration MSSC glassing unit. (WP4 and 6) Throughout the project the most promising new materials will be fabricated at a larger scale for process development of the 20 * 30cm modules6. This is an important step beyond lab scale devices fabrication, where many of the layers are processed via spin-coating, towards optimisation of the inks for large area coating processes, such as slot-dye coating. At the end of the project, a fully double glassed demonstrator unit will be created where all the layers, interconnects and external connectors are processed through industrially relevant methods as would be the case in a commercial glazed unit. This is relevant to the cost-effective production of industrial modules which promise to be commercially competitive for well-defined applications in the next decade.
Project Results:
We have made tremendous progress over the course of the project and below we describe the progress with respect to the different work packages and individual objectives.
WP1 – Material synthesis, fabrication and characterization
O1.1 Creation of a perovskite absorber with optimum bandgap for maximum
efficiency and enhanced stability
We have studied two perovskite families, namely the lead halides and the tin halide
perovskites. Initial promise was observed with the Sn halides, but the overall lack
of stability of these materials was not encouraging. However, in the second period of the project we discovered that if we process Pb:Sn mixed metals and employ FA or mixtures of FA and Cs as the cations we can achieve orders of magnitude improvement in the stability of the materials and low band gap perovskite solar cells with up to 15% efficiency.
For the Pb based materials, in the first period we discovered that formamidinium (FA) is a
much more ideal organic cation than MA, in both operational peroformance and stability. The
FAPbI3 and mixed cation perovskite FA/MAPbI¬3 was the most promising material and lower
more ideal bandgap than the MAPbI3. In the second period we discovered that the FAPbI3 compound has a structural instability, where it converts to a yellow non-perovskite phase at room temperature. We have overcome this however by mixing FA with the smaller Cs cation. This mixed cation perovskite now delivers remarkable stability, excellent performance and also enables band gap tuneability.
O1.2 Conceive and create an advanced organic hole-conductor with superior
performance and stability in MSSCs
Much work has been conducted with new HTMs sythesised by Kanaus. These have been
screened at EPFL and UOXF and a number of materials competitive with spiro-OMETAD
have emerged. The finding which we have made within this project is that the original HTM,
spiro-OMeTAD does not appear to pose a critical limitation for performance. However, it is
complex to syntheise, so these newly developed materials are targeting more simple
synthetic routes to achieve lower cost. During the second period we have synthesisied a number of new HTMs which work as well as spiro-OMeTAD in the solar cells, but which are much cheaper to synthesize. These could represent viable options for commercialization.
O1.3 Realise an optimum low termperature processed scaffold for MSSCs
The low temperature processed scaffold is mesoporous alumina of approximately 300nm thickness. The real emergence from this project is that no scaffold deliveres equally good performance, hence the optimum low temperature processed device is the planar heterojunction perovskite solar cells.
O1.4 Realise an optimum glass coated TCO/n-type collection layer for MSSCs
The TiO2 coated FTO glass which was sourced from Nipon Sheet Glass has proven to be very effective at inducing improved rectification in the solar cells. However, the solar cells with the NSG FTO/TiO2 layers exhibited quite sever hysteresis in the current voltage curves and low stabalised power output. within the project we have discovered that modifying TiO2 with an organic electron acceptor, such as C60 greatly enhances the quality of the TiO2/perovskite heterojunction. This has been demonstrated very clearly with low temperature processed TiO2 nanopartciles coated with a layer of PC61BM, a fullerenen derivative. We have also found that sol-gel processed SnO2/PC61BM and SnO2/C60 layers make very effective and very stable n-type charge collection layers. The collection layer of choice for efficiency, stability and cost is SnO2/C60
O1.5 Tandem tunnel junction
We have investigated means to make p-n organic-inorganic tunnel junctions for the perovskite solar cells. The first attempts were made with PEDOT:PSS/TiO2 and some other approaches adopted from the organic PV community. In parallel we have been developing the perovskite solar cell to be robust to ITO deposition. We have now managed to develop a reproducible route to sputter coat ITO on top of the perovskite cells. In the inverted architecture we have combined this with PEDOT:PSS to create the recombination-junction/hole collection layer. On top of Silicon cells, we have used a double layer of ITO/SnO2 with the optional additional layer of C60 to make the recombination junction.
WP2 – Device integration and testing
O2.1 Realise a 16% efficient single junction MSSC by incorporating the new materials developed in WP1, assisted by the enhanced fundamental knowledge in WP3 and processing know-how.
We have greatly surpasses the targeted efficiency in devices with both planar heterojunction and mesoporous TiO2. A key achievement is the realisation of >18% efficient planar hetetrojunction solar cell with a C60 n-type collection layer. Also the realisation of >21% efficiency with a thin mesoporus TiO2 layer is notable. A challenge with the thin TiO2 inter-layer is to develop this into a low temperature processed route.
O2.2 Realise an MSSC:c-Si tandem cell with over 21% efficiency to gain expertise in the integration of MSSC top cells on a well optimised bottom cell technology, whilst also expanding the impact of MESO to the broader EU PV community.
We have realised monolithic perovskite silicon tandem solar cell at ~ 22 % efficiency. We have also worked out a means to deposit transparent conducting oxide ITO on top of a perovskite solar cell which gives a single junction perovskite solar cell of 15% with very good transmission in the near IR. Through making a 4-terminal tandem cell with a perovskite cell with semi-transparent electrodes, and a silicon HIT cell, we have delivered 4T tandem efficiency of ~22.5%, but identify a clear path to surpassing 25% .
O2.3 Realise a 19% efficient all MSSC tandem cell by integrating a low loss tunnel junction and incorporating the new perovskite absorbers and HTMS, understanding and know how developed in MESO.
We have made tremendous breakthrough in the 2nd period with high efficiency Pb:Sn perovskites and have realised a 2T all perovskite tandem cell at 17% efficiency and a 4T all perovskite tandem cell at 20.3% efficiency.
WP3 – Fundamental investigations and modelling
O3.1 Structural optical property relationship
The presence of various types of chemical interactions give perovskite semiconductors a characteristic fluctuating structure sensitive to the operating conditions to which they adjust through a non-linear response. MESO has made key contributions to the understanding so far developed on the role of micro-structure in the photophysical properties of solution processable perovskites, highlighting the importance of interfaces at molecular level. First we have identified the markers for local disorder at molecular level by using Raman Spectroscopy as a probe. Then, we have explored the role of microstructure, and thin film processing, in determining the absorption and emission properties of the material. We have demonstrated that changing the chemical composition of the crystalline unit is not the only way to engineer the bandgap and photophysical processes in this class of semiconductors. By controlling the growth of the polycrystalline thin film it is possible to affect the conformational order of the crystalline unit, affecting both the electronic properties of the semiconductor and the activation energy of defect formation. The orientational dynamics of the organic A-cations is probably the most complex problem in the structural characterization of organohalide perovskites. The organic and inorganic perovskite components are strictly linked, so that a change in the orientation of the organic cations also implies a restructuring of the inorganic part. The implications of such dynamical interplay on the optoelectronic properties of organohalide perovskites can be investigated by probing the time evolution of the electronic structure as the nuclei fluctuate under the effect of thermal agitation, as probed by ab-initio molecular dynamics simulations. We have carried out simulations of the optical spectra of MAPbI3 at room temperature and at higher temperature, representative of the tetragonal and cubic phases, respectively. We experimentally observed a gradual blue-shift of the band-gap from room temperature to 410 K, which is not paralleled by the predictions of GW calculations for an abrupt change from the tetragonal to the cubic structure. Structural analyses revealed that the high temperature phase is indeed cubic when considering the time-averaged structure. Notably, however, the ‘‘cubic’’ structure can instantaneously strongly deviate from the nominal symmetric structure on a sub-ps time scale, with octahedral tilting values comparable to those observed for the tetragonal 320 K structure. When calculating the average band-gap, obtained by a series of calculations along the ab initio MD trajectory, we indeed recovery the experimental band-gap trend. This result explains the absence of dramatic changes in the light absorption onset of MAPbI3 perovskites across the explored temperature range. Most notably, we demonstrate that, as opposed to the ferroelectric properties of inorganic oxide perovskites, the photovoltaic properties of hybrid lead-halide perovskites are not inherently limited by the presence of a phase transition within the solar cell operating regime.
O3.2 Hybrid interface
The interface between the HTM and the perovskite is very important for extracting holes. As a matter of fact, engineering of specifically tailored-HTMs compatible with the perovskite surface was proven to improve the PV efficiency compared to the standard Spiro-MeOTAD HTM.
However, the work in MESO has identified that the n-type TiO2/perovskite interface is most critical in controlling the operation of the solar cells. Theoretical work has shown that this interface could potentially give rise to a different defect distribution than in the bulk, with accumulation of negatively charge defects (e.g. iodine vacancies) at the TiO2 side. Alongside, we have experimentally established that electrons are predominantly trapped in a broad distribution of deep trap states. This has important implications in the design of the device architecture, in particular for the choice of the charge extracting layer. Importantly it also rationalizes and reconciles all those reports which indicate that the choice of the electron extracting layer is crucial for the electrical stability of the solar cell (i.e. hysteresis) and that ion motion cannot justify, as the only phenomenon, the polarization effects in perovskite based optoelectronic devices. A combined experimental/theoretical study has indeed reported on the effect of PbI2 on the perovskite/TiO2 heterojunction electronic properties, showing that the presence of excess PbI2 favorably modifies the energy levels alignment and the interfacial electronic coupling, which can ease the interfacial electron transfer. Through these investigations we have identified certain superior properties of the hybrid interface between the n-type organic (C60 or PCBM) and the perovskite. This interface is a superior planar interface. We note that all the interfaces studied so far do induce non-radiative recombination at the heterojunction. A challenge in order to reach the limiting efficiencies (theoretically above 30%) will be to switch off the non-radiative decay at these heterojunctions
O3.3 Structural electronic property relationship
A property intimately connected to spin-orbit coupling is the so-called Rashba band splitting, which has received considerable attention from a theoretical point of view. The Rashba effect is the consequence of the breaking of inversion symmetry in the crystal in a direction orthogonal to a k-point sampling plane, leading to a band splitting in momentum space which could possibly drive the materials towards an indirect band-gap semiconductor. The consequences of this band-splitting could be then related to reduced carrier recombination in organohalide perovskites, leading to high PV efficiency. Motivated by the huge interest in understanding carrier recombination in organohalide perovskites, we have investigated the interplay of electronic (via first principles band-structure calculations) and nuclear (via ab initio molecular dynamics simulations) degrees of freedom in defining the Rashba splitting in realistic MAPbI3 models under thermal conditions. Our simulations have disclosed the temporal and spatial scale of the “dynamical Rashba effect” in MAPbI3, allowing for a quantification of the magnitude of this effect under realistic conditions. We find that even in a globally centrosymmetric structure, likely representing the average MAPbI3 crystal at room temperature, the fluctuations of the coupled inorganic/organic degrees of freedom give rise to a spatially local Rashba effect which fluctuates on the sub-ps time scale typical of the methylammonium cation dynamics. This is in turn consistent with the organic cation motion representing the driving symmetry breaking element in the MAPbI3 crystal. Our results shed light on the impact of the observed dynamical Rashba effect in contributing to reduced carrier recombination in MAPbI3, a property likely lying at the heart of perovskite solar cells efficiency.
O3.4 Best perovskite HTM combination
We have found that spior-OMeTAD is prohibitibvely expensive due to its complicated many step syntheisis. We have designed and realized a number of new HTMs and three of them are specifically successful, V866, V859 and V950. These work well with both the original work-horse MAPbI3 perovskite, and also the contemporary, FA0.83Cs0.17Pb(I0.6Br0.4)3 perovskite.
WP4 – Scale up
O4.1 Assess the scalability and viability of the new materials developed in the
MESO project (cost, abundance and toxicity)
We have confirmed that the Pb based perovskite is not prohibited for inclusion within a
solar cell module. The material will be subject to certain regulations which will stipulate end
of life recycling. The new hole transporters have been developed are based on more simpler lower cost synthetic procedures and will hence help to reduce the overall materials cost for the perovskite solar cells.
C60 has been found to be an excellent organic n-type charge collection materials, and only costing 16 Euros/g at research scale is entirely compatible with use at scale.
O4.2 Achieve uniform processing of the new materials
The new materials have been deposited over large area by slot dye coating, spin-coating and thermal evaporation. The developments have been comparing one pot routes to sequential routes where the PbI2 is deposited before the MAI or FAI. For the Pb:Sn based low band gap perovskites, we have developed a new solution processing route by combining mixed solvents (DMF and DMSO) with an antisolvet bath (Anisole) which has delivered very uniform films with high quality. This was one of the key reasons for the breakthrough the with Sn;Pb based perovskites.
O4.3 Realise manufacturing process for complete modules incorporating MESO
technology
The baseline modules manufacturing route was identified including laser etching and stringing of multiple cells together on 20*30cm substrate sizes. During the second period of the project a shift in emphasis towards the perovskite-on-silicon tandem cell took place, and the 2nd stage and final modules have been constructed via stringing large cells together in a similar fashion to the conventional crystalline silicon modules.
WP5 – Stability
O5.1 To determine and minimize the impact of moisture and oxygen on long term
MSSC stability
After a number of detailed characterizations we have identified that moisture is the primary driver for degradation of the perovskite, with the degradation accelerated by the temperature. We have identified that the primary decomposition process is the loss of methylamonium ions and the degradation of the perovskite to PbI2. Fortuitously a small amount of PbI2 generation does not seem to critically impact the performance of the solar cell, hence the system is unusually tolerant to partial degradation. In the second period we have discovered that replacing MA with FA/Cs mixed anions is extremely beneficial towards moisture/oxygen and temperature degradation.
O5.2 Minimise any detrimental impact of heating or cooling the cell between -40
and +85 degrees Celsius
To overcome the issue of thermal stability we have found that substation of the methylamonium action with formamidinium is very effective and films composed of FAPbI3 are thermally stable at 150 degrees, far beyond the operational temperature of the solar cells. However, FAPbI3 is know to have a structural instability and convert to the yellow phase at room temperature. We have found that this conversion only occurs in the presence of moisture, and hence effective encapsulation can prevent this transformation occurring. As such we have shown over 50 cycles of films of FAPbI3 between -40 and +85 degrees without any signature of conversion to the yellow phase. We have now shown 200 thermal cycles of complete perovskite-on-silicon tandem cells to exhibit less than 5% degradation in performance. We have hence minimized any detrimental impact by A-site cation choice.
O5.3 Select the module package for optimum stability compatible with MSSC
technology
Through a series of tests we have selected a suitable laminate foil which suitably protects the perovskite films for 85 degrees centigrade and 85% RH. This has been employed in the longer term environmental testing.
O5.4 Pass IEC61646 thin film solar cell environmental stressing protocol
Fundamental stability of the materials and devices looks set to pass the IEC61646 stressing protocol. Internal tests have now been passed and the perovskite-on-silicon cells have been sent off for external certification tests.
WP6 – Demonstrator
O6.1 Create working demonstrator solar cell modules incorporating the materials
developed within the MESO project
The baseline demonstrator was created as a 20*30cm monolithic thin film modules. The Stage 1 Stage 2 demonstrators have been created as perovskite-on-silicon cells strung together into 4-cell minimodules. Stage 1 were 4” wafer cells and stage 2 were 6” wafer cells.
Potential Impact:
The work within MESO has had a remarkable impact upon the academic scientific community: The MESO project is centred on the perovskite solar cell technology, where the perovskite absorbers were only discovered to deliver efficient solid-state photovoltaics the year prior to the commencement of the MESO project. The scientific output from the MESO project has captivated the research community, and encouraged 1000’s of researchers to turn their hand to developing perovskite semiconductors and solar cells. As an exemplification of this, the number of papers published on perovskite solar cells in 2012 was only 4, in 2013 this number rose to 60, and to-date more than 3000 papers have published on the topic (as assessed by searching perovskite solar cell* in web of science). To also illustrate the MESO consortiums central involvement in this scientific impact, in 2013 the Coordinator was named one of “Natures Ten” people who mattered, by Nature Magazine, due to their breakthroughs in perovskites, and in 2016, 3 investigators from the consortium were named in the top 19 “most influential minds” by Thomson Reuters, primarily due to their research outputs in the field of perovskite solar cells. The Magnitude and quality of publication reported on the MESO project, also pays homage to the remarkable impact of this work.
Moving beyond science, the reason why the area of research has garnered such interest, is due to the imminent promise of perovskite solar cells delivering a technology which can surpass the performance to cost ratio of existing PV technologies. Specifically with respect to the impacts listed in the original call:
(i) Efficiency of an OPV module of at least 15% in a relevant environment, with a considerable improvement in the service life-time, performance of the materials to be credibly planned to be reachable by 2030; We have pushed the efficiency of perovskite based solar cells, which have emerged from organic based PV research, beyond 21%, which is well beyond the 15% efficiency mark. In addition through moving towards multi-junction architectures we have outlined a roadmap to move beyond 30% efficiency in the long run.
(iii) More favourable cost/efficiency ratio compared to inorganic PV.
The perovskite technology has proven to become as efficient as inorganic PV, and the perovskite-on-silicon tandems promise to be more efficient in the near term. Therefore, provided that the cost of manufacturing is less than, or equal to the cost of manufacturing inorganic PV, the cost/efficiency ratio will be higher. It is very likely that the cost of manufacturing perovskites will indeed be lower than the cost of manufacturing inorganic PV, due to the low temperature of processing, and low cost manufacturing routes. However, this cost model will be developed further in future programs following on from MESO.
(iv) Contributions to the implementations of the SET plan, in particular to the Materials Roadmap enabling Low Carbon Energy Technologies. “Up to 15% of the EU electricity will be produced by solar energy in 2020. However, if the DESERTEC vision is achieved, the contribution of solar energy will be higher in the longer term.” The MSSC appears to “decouple” high cost from potential high efficiency, and if pushed to maturity will be capable of delivering solar energy on the very largest scale, and much larger than predicted by current technologies. In this project a new family of semiconducting perovskite materials and semiconducting organic hole-conductors have been developed. Prior to this research activity, perovskites had barely been considered as serious materials for low carbon energy technologies. This project has been the first pan-European effort to catapult these materials to the forefront. In addition to the organic-inorganic perovskites, organic hole-conductors specifically tuned for optimised solar cell operation, has resulted in a new library of transparent hole-conductors enabling this technology and likely to have broader reaching applications.
List of Websites:
http://meso-solar.eu/
In this project we developed a new class of low cost solution processible hybrid solar cells based on metal halide perovskite absorbers and organic or metal oxide charge collection layers. This “heterojunction” solar cell technology proved to be remarkably efficient on its first reduction to practice, and over the course of the project has now shown tremendous scope to compete with the very best crystalline semiconductor and thin film technologies on efficiency, while offering the very lowest potential cost for materials and solution processed manufacturing. On the granting of MESO, our targeted end of project efficiency for single junction perovskite solar cells was “an ambitious” 16%. However, the technical progress over the course of the project has been unexpectedly rapid, and this target has been smashed, with us having presented devices delivering over 21% power conversion efficiency. The activities in MESO have spanned from synthesis of new organic-inorganic perovskite absorbers and organic hole-conductors, theoretical modelling, through thin film deposition and integration, device optimization, characterisation and advanced spectroscopy, to scale-up, stability enhancement and certification and demonstrator mini-module manufacture. Our consortium consists of leading academics in Europe; pioneers of hybrid solar cells, expert organic and inorganic synthetic capabilities, leaders in electronic energy level calculations, interfaces and device simulation, world class advanced spectroscopy, and a dynamic early stage technology company. This diverse yet perfectly complementary pan European consortium ensured that the MESO project delivered on its objectives, and is on track to realize a new commercial photovoltaic technology. Our achieved objectives have been to realise extremely efficient single junction perovskite solar cells, tandem perovskite solar cells by combining perovskite with silicon technologies and all perovskite tandem solar cells. Beyond efficiency, a key target has been to enable the perovskite technology to surpass the international standard thin film solar cell environmental stressing certification, IEC61646, and the perovskite-on-silicon tandem cells have surpassed both thermal cycling and damp heat IEC tests, in addition to 1000hrs full sun light soaking at 60C with less than 5% relative degradation in performance. This is a key milestone which has enabled the perovskite technology to move towards the next stage in the path towards industrialisation.
Project Context and Objectives:
This project brings together the leading research groups and industry in Europe investigating, developing and commercialising solid-state hybrid solar cells. The ambitious “concept” of the project is to take the perovskite based meso-superstructured solar cell from its first introduction to commercial launch within the 3 year project timeframe. This will be achieved by; i) developing new, ideally optimised materials (both organic hole-conductors and perovskite absorbers) delivering improved performance and stability; ii) optimising the processing and integration of these materials into manufacturable high efficiency devices and modules; iii) probing and understanding the fundamental processes occurring in the materials and operational solar cells to give a rational approach to the design and implementation of new materials. MESO is broken down into 5 RTD work packages (WPs), 1. Material Synthesis and characterisation, 2. Device Integration and testing, 3. Fundamental Investigations and modelling, 4. Scale-up, and 5. Stability enhancement, with an additional Demonstrator WP6. For each WP there is one or two key Objectives (O):
O1 Creation of a perovskite absorber with optimum bandgap for maximum efficiency and enhanced stability. (WP1) We will employ a combinatorial approach to screen perovskite structures and develop a library of materials with a range of electronic and optical properties. The starting choices will largely be based on available literature on perovskites, however, new material families will also be computationally screened to predict their electronic and optical properties. The key challenges are: 1. Tune the band gap: To move the absorption onset out to 940nm (1.3eV) for the single junction solar cells, and to 730nm (1.7eV) and 1100nm (1.1eV) onset for optimum absorbers in a tandem junctions. 2. Enhance the stability: Reduced moisture and oxygen sensitivity will be achieved by employing non-hygroscopic cationic organic ligands and tuning the inorganic metal cations and halide or chalcogenide anions. 3. Optimise the level of doping: In addition to having the ideal band gap and stability, since the perovskite functions as both the absorber and n-type charge transporter in the MSSC, it is essential that its level of doping is optimised. This will be achieved by using mixed anions and doping with different metal cations. This objective relates to innovative materials, improved stability and better control of the band-gap addressed by the call.
O2 Conceive and create an advanced organic hole-conductor with superior performance and stability in MSSCs. (WP1) We will undertake a synthetic strategy to develop a new family of hole-conducting molecules, and oligomers to polymers which have high mobility and tuneable highest occupied molecular orbitals (HOMOs) to maximise hole-transfer efficiency, and open-circuit voltage, while minimising series resistance and recombination losses. We will also address thermal and UV-stability issues to enable long term performance. Ab initio computer simulations will assist the design of new materials with target electronic and optical properties. This relates to novel organic semiconductors with an improved thermal and photochemical stability in combination with a higher power conversion efficiency addressed by the call.
O3 Realise an optimum low temperature processed scaffold for MSSCs (WP1/ WP2) will be achieved by finding the optimum porosity, meso-scale and material type for the mesoporous scaffold (WP1). Subsequent device optimisation with the low temperature paste will lead to a successful outcome (WP2). This relates to advances in non-vacuum coating and printing techniques, and in addition to enabling tandem cell construction as targeted in this project, it will enable flexibility and economically interesting processing technologies, as addressed in the call.
O4 Realise an optimum glass coated TCO/n-type collection layer for MSSCs. (WP1/ WP2/ WP5/ WP6) will be achieved by developing higher transparency, lower sheet resistivity coated glass than FTO. This Objective is especially relevant to the scale up and demonstrator activities in WP4 and WP6.
O5 Tandem tunnel junction realise a processible highly transparent, low resistance tunnel-junction for multi-junction MSSCs.(WP1/WP2/WP5)
O6 Demonstration of an MSSC single junction solar cell with greater than 16% efficiency (WP2) will be achieved by combing the new materials developed in WP1, with optimised processing, including variations in, alumina scaffold film thickness, perovskite and hole-transporter concentrations and coating conditions, level of doping in the perovskite and hole-conductor, perovskite drying temperature and time etc..
O7 Demonstration of a 21% efficient hybrid tandem-junction MSSC on c-Si (WP2). To kick start the tandem activity and enable broader adoption of the MSSC across the PV community it is an objective to demonstrate enhanced c-Si solar cell efficiency by combining with our baseline MSSC as a two terminal monolithic hybrid tandem solar. This relates to better cost/efficiency ratio as compared to conventional PV.
O8 Demonstration of a 19% efficient tandem-junction MSSC (WP2). Realising a low temperature route to the MSSC opens up the possibility of monolithic tandem solar cells. We will follow the route tried and tested in OPV of using a conducting p-type polymer (PEDOT:PSS) and n-type metal oxide (TiO2 or ZnO) as the tunnel junction. The device architecture will consist of a wide gap front cell (1.7eV band gap) coated with PEDOT:PSS/TiO2 (or ZnO) tunnel junction with a narrow gap rear cell. O4 and O5 relate to a higher power conversion efficiency and production of (certified) reference materials addressed from the call
O9 Full understanding of the operation of the solar cell and performance limiting factors. (WP3) By combining a broad range of advanced optical spectroscopy and electronic characterisation tools, along-side first principle materials and device modelling, we will develop a comprehensive understanding of the fundamental optical and electronic processes occurring in the materials and the operation of the complete devices. This knowledge will be invaluable to help redirect the materials synthesis and device engineering efforts throughout the project. This relates to, a better understanding of the long term stable operation and the degradation mechanisms at the material level, addressed by the call.
O10 Demonstration of certifiable solar cell stability. (WP5) There is no certain means to ensure a solar technology will last for 25 years, without having it in the filed for 25 years. However, since this is infeasible in the timeframe of product development to market, and indeed in the timeframe of this project, accelerated testing will be employed. We will age the solar cells at 85°C under simulated full sun illumination with the target of achieving less than 20% drop in performance after 1000hrs illumination. 25 years is approximately 54,750 hrs full sun illumination, assuming the equivalent of 6 hrs full sun light/day, or 250Wm 2 average irradiance (equivalent to North Africa). Taking a standard acceleration factor of 2 for each ten degrees increase in temperature, an acceleration factor of 64 is estimated for 85 °C as opposed to 25 °C degrees, and hence the 54,750 hrs equivalent would be reached before 1000 hrs. However, although this will give confidence, the standard solar cell accreditation requires a series of stress tests including temperature cycling and damp heat. We will stress our cells to 5 of the most critical tests in the IEC61646 thin film standard certification internally, and identify and eradicate failure mechanisms. A set of 8 modules will then be subject to IEC61646 at an accredited test facility. It is an objective that they pass this test. This relates to a better understanding of the long term stable operation and the degradation mechanisms at the material level can contribute to increasing the lifetime of the cells, which should be targeted, and production of (certified) reference materials addressed by the call.
O11 The scale-up of the processing to minimodule and the creation of a demonstration MSSC glassing unit. (WP4 and 6) Throughout the project the most promising new materials will be fabricated at a larger scale for process development of the 20 * 30cm modules6. This is an important step beyond lab scale devices fabrication, where many of the layers are processed via spin-coating, towards optimisation of the inks for large area coating processes, such as slot-dye coating. At the end of the project, a fully double glassed demonstrator unit will be created where all the layers, interconnects and external connectors are processed through industrially relevant methods as would be the case in a commercial glazed unit. This is relevant to the cost-effective production of industrial modules which promise to be commercially competitive for well-defined applications in the next decade.
Project Results:
We have made tremendous progress over the course of the project and below we describe the progress with respect to the different work packages and individual objectives.
WP1 – Material synthesis, fabrication and characterization
O1.1 Creation of a perovskite absorber with optimum bandgap for maximum
efficiency and enhanced stability
We have studied two perovskite families, namely the lead halides and the tin halide
perovskites. Initial promise was observed with the Sn halides, but the overall lack
of stability of these materials was not encouraging. However, in the second period of the project we discovered that if we process Pb:Sn mixed metals and employ FA or mixtures of FA and Cs as the cations we can achieve orders of magnitude improvement in the stability of the materials and low band gap perovskite solar cells with up to 15% efficiency.
For the Pb based materials, in the first period we discovered that formamidinium (FA) is a
much more ideal organic cation than MA, in both operational peroformance and stability. The
FAPbI3 and mixed cation perovskite FA/MAPbI¬3 was the most promising material and lower
more ideal bandgap than the MAPbI3. In the second period we discovered that the FAPbI3 compound has a structural instability, where it converts to a yellow non-perovskite phase at room temperature. We have overcome this however by mixing FA with the smaller Cs cation. This mixed cation perovskite now delivers remarkable stability, excellent performance and also enables band gap tuneability.
O1.2 Conceive and create an advanced organic hole-conductor with superior
performance and stability in MSSCs
Much work has been conducted with new HTMs sythesised by Kanaus. These have been
screened at EPFL and UOXF and a number of materials competitive with spiro-OMETAD
have emerged. The finding which we have made within this project is that the original HTM,
spiro-OMeTAD does not appear to pose a critical limitation for performance. However, it is
complex to syntheise, so these newly developed materials are targeting more simple
synthetic routes to achieve lower cost. During the second period we have synthesisied a number of new HTMs which work as well as spiro-OMeTAD in the solar cells, but which are much cheaper to synthesize. These could represent viable options for commercialization.
O1.3 Realise an optimum low termperature processed scaffold for MSSCs
The low temperature processed scaffold is mesoporous alumina of approximately 300nm thickness. The real emergence from this project is that no scaffold deliveres equally good performance, hence the optimum low temperature processed device is the planar heterojunction perovskite solar cells.
O1.4 Realise an optimum glass coated TCO/n-type collection layer for MSSCs
The TiO2 coated FTO glass which was sourced from Nipon Sheet Glass has proven to be very effective at inducing improved rectification in the solar cells. However, the solar cells with the NSG FTO/TiO2 layers exhibited quite sever hysteresis in the current voltage curves and low stabalised power output. within the project we have discovered that modifying TiO2 with an organic electron acceptor, such as C60 greatly enhances the quality of the TiO2/perovskite heterojunction. This has been demonstrated very clearly with low temperature processed TiO2 nanopartciles coated with a layer of PC61BM, a fullerenen derivative. We have also found that sol-gel processed SnO2/PC61BM and SnO2/C60 layers make very effective and very stable n-type charge collection layers. The collection layer of choice for efficiency, stability and cost is SnO2/C60
O1.5 Tandem tunnel junction
We have investigated means to make p-n organic-inorganic tunnel junctions for the perovskite solar cells. The first attempts were made with PEDOT:PSS/TiO2 and some other approaches adopted from the organic PV community. In parallel we have been developing the perovskite solar cell to be robust to ITO deposition. We have now managed to develop a reproducible route to sputter coat ITO on top of the perovskite cells. In the inverted architecture we have combined this with PEDOT:PSS to create the recombination-junction/hole collection layer. On top of Silicon cells, we have used a double layer of ITO/SnO2 with the optional additional layer of C60 to make the recombination junction.
WP2 – Device integration and testing
O2.1 Realise a 16% efficient single junction MSSC by incorporating the new materials developed in WP1, assisted by the enhanced fundamental knowledge in WP3 and processing know-how.
We have greatly surpasses the targeted efficiency in devices with both planar heterojunction and mesoporous TiO2. A key achievement is the realisation of >18% efficient planar hetetrojunction solar cell with a C60 n-type collection layer. Also the realisation of >21% efficiency with a thin mesoporus TiO2 layer is notable. A challenge with the thin TiO2 inter-layer is to develop this into a low temperature processed route.
O2.2 Realise an MSSC:c-Si tandem cell with over 21% efficiency to gain expertise in the integration of MSSC top cells on a well optimised bottom cell technology, whilst also expanding the impact of MESO to the broader EU PV community.
We have realised monolithic perovskite silicon tandem solar cell at ~ 22 % efficiency. We have also worked out a means to deposit transparent conducting oxide ITO on top of a perovskite solar cell which gives a single junction perovskite solar cell of 15% with very good transmission in the near IR. Through making a 4-terminal tandem cell with a perovskite cell with semi-transparent electrodes, and a silicon HIT cell, we have delivered 4T tandem efficiency of ~22.5%, but identify a clear path to surpassing 25% .
O2.3 Realise a 19% efficient all MSSC tandem cell by integrating a low loss tunnel junction and incorporating the new perovskite absorbers and HTMS, understanding and know how developed in MESO.
We have made tremendous breakthrough in the 2nd period with high efficiency Pb:Sn perovskites and have realised a 2T all perovskite tandem cell at 17% efficiency and a 4T all perovskite tandem cell at 20.3% efficiency.
WP3 – Fundamental investigations and modelling
O3.1 Structural optical property relationship
The presence of various types of chemical interactions give perovskite semiconductors a characteristic fluctuating structure sensitive to the operating conditions to which they adjust through a non-linear response. MESO has made key contributions to the understanding so far developed on the role of micro-structure in the photophysical properties of solution processable perovskites, highlighting the importance of interfaces at molecular level. First we have identified the markers for local disorder at molecular level by using Raman Spectroscopy as a probe. Then, we have explored the role of microstructure, and thin film processing, in determining the absorption and emission properties of the material. We have demonstrated that changing the chemical composition of the crystalline unit is not the only way to engineer the bandgap and photophysical processes in this class of semiconductors. By controlling the growth of the polycrystalline thin film it is possible to affect the conformational order of the crystalline unit, affecting both the electronic properties of the semiconductor and the activation energy of defect formation. The orientational dynamics of the organic A-cations is probably the most complex problem in the structural characterization of organohalide perovskites. The organic and inorganic perovskite components are strictly linked, so that a change in the orientation of the organic cations also implies a restructuring of the inorganic part. The implications of such dynamical interplay on the optoelectronic properties of organohalide perovskites can be investigated by probing the time evolution of the electronic structure as the nuclei fluctuate under the effect of thermal agitation, as probed by ab-initio molecular dynamics simulations. We have carried out simulations of the optical spectra of MAPbI3 at room temperature and at higher temperature, representative of the tetragonal and cubic phases, respectively. We experimentally observed a gradual blue-shift of the band-gap from room temperature to 410 K, which is not paralleled by the predictions of GW calculations for an abrupt change from the tetragonal to the cubic structure. Structural analyses revealed that the high temperature phase is indeed cubic when considering the time-averaged structure. Notably, however, the ‘‘cubic’’ structure can instantaneously strongly deviate from the nominal symmetric structure on a sub-ps time scale, with octahedral tilting values comparable to those observed for the tetragonal 320 K structure. When calculating the average band-gap, obtained by a series of calculations along the ab initio MD trajectory, we indeed recovery the experimental band-gap trend. This result explains the absence of dramatic changes in the light absorption onset of MAPbI3 perovskites across the explored temperature range. Most notably, we demonstrate that, as opposed to the ferroelectric properties of inorganic oxide perovskites, the photovoltaic properties of hybrid lead-halide perovskites are not inherently limited by the presence of a phase transition within the solar cell operating regime.
O3.2 Hybrid interface
The interface between the HTM and the perovskite is very important for extracting holes. As a matter of fact, engineering of specifically tailored-HTMs compatible with the perovskite surface was proven to improve the PV efficiency compared to the standard Spiro-MeOTAD HTM.
However, the work in MESO has identified that the n-type TiO2/perovskite interface is most critical in controlling the operation of the solar cells. Theoretical work has shown that this interface could potentially give rise to a different defect distribution than in the bulk, with accumulation of negatively charge defects (e.g. iodine vacancies) at the TiO2 side. Alongside, we have experimentally established that electrons are predominantly trapped in a broad distribution of deep trap states. This has important implications in the design of the device architecture, in particular for the choice of the charge extracting layer. Importantly it also rationalizes and reconciles all those reports which indicate that the choice of the electron extracting layer is crucial for the electrical stability of the solar cell (i.e. hysteresis) and that ion motion cannot justify, as the only phenomenon, the polarization effects in perovskite based optoelectronic devices. A combined experimental/theoretical study has indeed reported on the effect of PbI2 on the perovskite/TiO2 heterojunction electronic properties, showing that the presence of excess PbI2 favorably modifies the energy levels alignment and the interfacial electronic coupling, which can ease the interfacial electron transfer. Through these investigations we have identified certain superior properties of the hybrid interface between the n-type organic (C60 or PCBM) and the perovskite. This interface is a superior planar interface. We note that all the interfaces studied so far do induce non-radiative recombination at the heterojunction. A challenge in order to reach the limiting efficiencies (theoretically above 30%) will be to switch off the non-radiative decay at these heterojunctions
O3.3 Structural electronic property relationship
A property intimately connected to spin-orbit coupling is the so-called Rashba band splitting, which has received considerable attention from a theoretical point of view. The Rashba effect is the consequence of the breaking of inversion symmetry in the crystal in a direction orthogonal to a k-point sampling plane, leading to a band splitting in momentum space which could possibly drive the materials towards an indirect band-gap semiconductor. The consequences of this band-splitting could be then related to reduced carrier recombination in organohalide perovskites, leading to high PV efficiency. Motivated by the huge interest in understanding carrier recombination in organohalide perovskites, we have investigated the interplay of electronic (via first principles band-structure calculations) and nuclear (via ab initio molecular dynamics simulations) degrees of freedom in defining the Rashba splitting in realistic MAPbI3 models under thermal conditions. Our simulations have disclosed the temporal and spatial scale of the “dynamical Rashba effect” in MAPbI3, allowing for a quantification of the magnitude of this effect under realistic conditions. We find that even in a globally centrosymmetric structure, likely representing the average MAPbI3 crystal at room temperature, the fluctuations of the coupled inorganic/organic degrees of freedom give rise to a spatially local Rashba effect which fluctuates on the sub-ps time scale typical of the methylammonium cation dynamics. This is in turn consistent with the organic cation motion representing the driving symmetry breaking element in the MAPbI3 crystal. Our results shed light on the impact of the observed dynamical Rashba effect in contributing to reduced carrier recombination in MAPbI3, a property likely lying at the heart of perovskite solar cells efficiency.
O3.4 Best perovskite HTM combination
We have found that spior-OMeTAD is prohibitibvely expensive due to its complicated many step syntheisis. We have designed and realized a number of new HTMs and three of them are specifically successful, V866, V859 and V950. These work well with both the original work-horse MAPbI3 perovskite, and also the contemporary, FA0.83Cs0.17Pb(I0.6Br0.4)3 perovskite.
WP4 – Scale up
O4.1 Assess the scalability and viability of the new materials developed in the
MESO project (cost, abundance and toxicity)
We have confirmed that the Pb based perovskite is not prohibited for inclusion within a
solar cell module. The material will be subject to certain regulations which will stipulate end
of life recycling. The new hole transporters have been developed are based on more simpler lower cost synthetic procedures and will hence help to reduce the overall materials cost for the perovskite solar cells.
C60 has been found to be an excellent organic n-type charge collection materials, and only costing 16 Euros/g at research scale is entirely compatible with use at scale.
O4.2 Achieve uniform processing of the new materials
The new materials have been deposited over large area by slot dye coating, spin-coating and thermal evaporation. The developments have been comparing one pot routes to sequential routes where the PbI2 is deposited before the MAI or FAI. For the Pb:Sn based low band gap perovskites, we have developed a new solution processing route by combining mixed solvents (DMF and DMSO) with an antisolvet bath (Anisole) which has delivered very uniform films with high quality. This was one of the key reasons for the breakthrough the with Sn;Pb based perovskites.
O4.3 Realise manufacturing process for complete modules incorporating MESO
technology
The baseline modules manufacturing route was identified including laser etching and stringing of multiple cells together on 20*30cm substrate sizes. During the second period of the project a shift in emphasis towards the perovskite-on-silicon tandem cell took place, and the 2nd stage and final modules have been constructed via stringing large cells together in a similar fashion to the conventional crystalline silicon modules.
WP5 – Stability
O5.1 To determine and minimize the impact of moisture and oxygen on long term
MSSC stability
After a number of detailed characterizations we have identified that moisture is the primary driver for degradation of the perovskite, with the degradation accelerated by the temperature. We have identified that the primary decomposition process is the loss of methylamonium ions and the degradation of the perovskite to PbI2. Fortuitously a small amount of PbI2 generation does not seem to critically impact the performance of the solar cell, hence the system is unusually tolerant to partial degradation. In the second period we have discovered that replacing MA with FA/Cs mixed anions is extremely beneficial towards moisture/oxygen and temperature degradation.
O5.2 Minimise any detrimental impact of heating or cooling the cell between -40
and +85 degrees Celsius
To overcome the issue of thermal stability we have found that substation of the methylamonium action with formamidinium is very effective and films composed of FAPbI3 are thermally stable at 150 degrees, far beyond the operational temperature of the solar cells. However, FAPbI3 is know to have a structural instability and convert to the yellow phase at room temperature. We have found that this conversion only occurs in the presence of moisture, and hence effective encapsulation can prevent this transformation occurring. As such we have shown over 50 cycles of films of FAPbI3 between -40 and +85 degrees without any signature of conversion to the yellow phase. We have now shown 200 thermal cycles of complete perovskite-on-silicon tandem cells to exhibit less than 5% degradation in performance. We have hence minimized any detrimental impact by A-site cation choice.
O5.3 Select the module package for optimum stability compatible with MSSC
technology
Through a series of tests we have selected a suitable laminate foil which suitably protects the perovskite films for 85 degrees centigrade and 85% RH. This has been employed in the longer term environmental testing.
O5.4 Pass IEC61646 thin film solar cell environmental stressing protocol
Fundamental stability of the materials and devices looks set to pass the IEC61646 stressing protocol. Internal tests have now been passed and the perovskite-on-silicon cells have been sent off for external certification tests.
WP6 – Demonstrator
O6.1 Create working demonstrator solar cell modules incorporating the materials
developed within the MESO project
The baseline demonstrator was created as a 20*30cm monolithic thin film modules. The Stage 1 Stage 2 demonstrators have been created as perovskite-on-silicon cells strung together into 4-cell minimodules. Stage 1 were 4” wafer cells and stage 2 were 6” wafer cells.
Potential Impact:
The work within MESO has had a remarkable impact upon the academic scientific community: The MESO project is centred on the perovskite solar cell technology, where the perovskite absorbers were only discovered to deliver efficient solid-state photovoltaics the year prior to the commencement of the MESO project. The scientific output from the MESO project has captivated the research community, and encouraged 1000’s of researchers to turn their hand to developing perovskite semiconductors and solar cells. As an exemplification of this, the number of papers published on perovskite solar cells in 2012 was only 4, in 2013 this number rose to 60, and to-date more than 3000 papers have published on the topic (as assessed by searching perovskite solar cell* in web of science). To also illustrate the MESO consortiums central involvement in this scientific impact, in 2013 the Coordinator was named one of “Natures Ten” people who mattered, by Nature Magazine, due to their breakthroughs in perovskites, and in 2016, 3 investigators from the consortium were named in the top 19 “most influential minds” by Thomson Reuters, primarily due to their research outputs in the field of perovskite solar cells. The Magnitude and quality of publication reported on the MESO project, also pays homage to the remarkable impact of this work.
Moving beyond science, the reason why the area of research has garnered such interest, is due to the imminent promise of perovskite solar cells delivering a technology which can surpass the performance to cost ratio of existing PV technologies. Specifically with respect to the impacts listed in the original call:
(i) Efficiency of an OPV module of at least 15% in a relevant environment, with a considerable improvement in the service life-time, performance of the materials to be credibly planned to be reachable by 2030; We have pushed the efficiency of perovskite based solar cells, which have emerged from organic based PV research, beyond 21%, which is well beyond the 15% efficiency mark. In addition through moving towards multi-junction architectures we have outlined a roadmap to move beyond 30% efficiency in the long run.
(iii) More favourable cost/efficiency ratio compared to inorganic PV.
The perovskite technology has proven to become as efficient as inorganic PV, and the perovskite-on-silicon tandems promise to be more efficient in the near term. Therefore, provided that the cost of manufacturing is less than, or equal to the cost of manufacturing inorganic PV, the cost/efficiency ratio will be higher. It is very likely that the cost of manufacturing perovskites will indeed be lower than the cost of manufacturing inorganic PV, due to the low temperature of processing, and low cost manufacturing routes. However, this cost model will be developed further in future programs following on from MESO.
(iv) Contributions to the implementations of the SET plan, in particular to the Materials Roadmap enabling Low Carbon Energy Technologies. “Up to 15% of the EU electricity will be produced by solar energy in 2020. However, if the DESERTEC vision is achieved, the contribution of solar energy will be higher in the longer term.” The MSSC appears to “decouple” high cost from potential high efficiency, and if pushed to maturity will be capable of delivering solar energy on the very largest scale, and much larger than predicted by current technologies. In this project a new family of semiconducting perovskite materials and semiconducting organic hole-conductors have been developed. Prior to this research activity, perovskites had barely been considered as serious materials for low carbon energy technologies. This project has been the first pan-European effort to catapult these materials to the forefront. In addition to the organic-inorganic perovskites, organic hole-conductors specifically tuned for optimised solar cell operation, has resulted in a new library of transparent hole-conductors enabling this technology and likely to have broader reaching applications.
List of Websites:
http://meso-solar.eu/
