Highly Air Stable Tin Halide Perovskite Photovoltaics using a Bismuth Capped Copper Top Electrode.

An effective approach is reported to enhance the stability of inverted organo-tin halide perovskite photovoltaics based on capping the cathode with a thin layer of bismuth. Using this simple approach, unencapsulated devices retain up to 70% of their peak power conversion efficiency after up to 100 h testing under continuous one sun solar illumination in ambient air and under electrical load, which is exceptional stability for an unencapsulated organo-tin halide perovskite photovoltaic device tested in ambient air. The bismuth capping layer is shown to have two functions: First, it blocks corrosion of the metal cathode by iodine gas formed when those parts of the perovskite layer not protected by the cathode degrade. Second, it sequesters iodine gas by seeding its deposition on top of the bismuth capping layer, thereby keeping it away from the electro-active parts of the device. The high affinity of iodine for bismuth is shown to correlate with the high polarizability of bismuth and the prevalence of the (012) crystal face at its surface. Bismuth is ideal for this purpose, because it is environmentally benign, non-toxic, stable, cheap, and can be deposited by simple thermal evaporation at low temperature immediately after deposition of the cathode.

Assessing the suitability of copper thiocyanate as a hole-transport layer in inverted CsSnI3 perovskite photovoltaics.

We report the findings of a study into the suitability of copper (I) thiocyanate (CuSCN) as a hole-transport layer in inverted photovoltaic (PV) devices based on the black gamma phase (B-γ) of CsSnI3 perovskite. Remarkably, when B-γ-CsSnI3 perovskite is deposited from a dimethylformamide solution onto a 180-190 nm thick CuSCN film supported on an indium-tin oxide (ITO) electrode, the CuSCN layer is completely displaced leaving a perovskite layer with high uniformity and coverage of the underlying ITO electrode. This finding is confirmed by detailed analysis of the thickness and composition of the film that remains after perovskite deposition, together with photovoltaic device studies. The results of this study show that, whilst CuSCN has proved to be an excellent hole-extraction layer for high performance lead-perovskite and organic photovoltaics, it is unsuitable as a hole-transport layer in inverted B-γ-CsSnI3 perovskite photovoltaics processed from solution.