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Hybrid perovskites are recently developed photoactive semiconductors that hold great promise for next-generation solar cells, with devices incorporating them reaching certified efficiencies as high as 22.1%. [1] This high performance is coupled with a relative low cost, as perovskites comprise earth-abundant elements that are amenable to deposition from the solution-state by scalable, inexpensive printing processes. [2] Recent work has focused on improving their long-term stability with significant progress being reported in encapsulation techniques and scalability with the production of modulescale devices (100 cm 2 ) exhibiting efficiencies of over 11%. [3][4][5][6] These developments have resulted in efforts to commercialize perovskite solar cells; however, there is still concern over the potential to achieve the 25-year service lifetimes necessary to make perovskites a disruptive technology.Photoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. However, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. In this study, the cohesion energy of perovskites containing various cation combinations of methylammonium, formamidinium, cesium, butylammonium, and 5-aminovaleric acid is reported. A trade-off is observed between the mechanical integrity and the efficiency of perovskite devices. High efficiency devices exhibit decreased cohesion, which is attributed to reduced grain sizes with the inclusion of additional cations and PbI 2 additives. Microindentation hardness testing is performed to estimate the fracture toughness of single-crystal perovskite, and the results indicated perovskites are inherently fragile, even in the absence of grain boundaries and defects. The devices found to have the highest fracture energies are perovskites infiltrated into a porous TiO 2 /ZrO 2 /C triple layer, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability. Perovskite Solar CellsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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Device scale-up and long-term stability constitute two major hurdles that the emerging perovskite solar technology will have to overcome before commercialization. Here, a comparative study was performed between ZnO and TiO2 electron-selective layers, two materials that allow the low-temperature processing of perovskite solar cells on polymer substrates. Although the use of TiO2 is well established on glass substrates, ZnO was chosen because it can be readily printed at low temperature and offers the potential for the large-scale roll-to-roll manufacturing of flexible photovoltaics at a low cost. However, a rapid degradation of CH3 NH3 PbI3 was observed if it was deposited on ZnO, therefore, the influence of the perovskite film preparation conditions on its morphology and degradation kinetics was investigated. This study showed that CH3 NH3 PbI3 could withstand a higher temperature on TiO2 than ZnO and that TiO2-based perovskite devices were more stable than their ZnO analogues.

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For the roll to roll production of truly flexible, cost effective solar cells, alternatives are needed to replace indium tin oxide, which conventionally serves as the transparent electrode. In this work, silver nanowire/PEDOT:PSS based electrodes are processed onto PET substrates by a scalable, roll-to-roll slot-die process. These electrodes are extensively characterized and incorporated into ITO-free, flexible perovskite solar cells to achieve a champion efficiency of 11%, comparable to ITO controls on glass. Furthermore, all of the device layers, except the top electrode, were deposited under ambient conditions. Preliminary device bending tests showed negligible change in efficiency after 10 000 compressive bends to a 5 mm radius. This progress is key to the manufacture of cheap, flexible perovskite solar cells by low temperature processing techniques.

One of the biggest challenges for making dye-sensitised solar cells (DSCs) on plastic substrates is the difficulty in making good quality nanoporous TiO 2 films with both good mechanical stability and high electrical conductivity. Cold isostatic pressing (CIP) is a powder compaction technique that applies an isostatic pressure to a powder sample in all directions. It is particularly suitable for making thin films on plastic substrates, including non-flat surfaces. Cold isostatically pressed nanocrystalline TiO 2 electrodes with excellent mechanical robustness were prepared on indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrates in the absence of organic binders and without heat treatment. The morphology and the physical properties of the TiO 2 films prepared by the CIP method were found to be very compatible with requirements for flexible DSCs on plastics. This room-temperature processing technique has led to an important technical breakthrough in producing high efficiency flexible DSCs. Devices fabricated on ITO/PEN films by this method using standard P-25 TiO 2 films with a Ru-complex sensitiser yielded a maximum incident photon-to-current conversion efficiency of 72% at the wavelength of 530 nm and showed high conversion efficiencies of 6.3% and 7.4% for incident light intensities of 100 and 15 mW cm −2 , respectively, which are the highest power conversion efficiencies achieved so far for any DSC on a polymer substrate using the widely used, commercially available P-25 TiO 2 powder.