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

Abstract

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.

Tin-Based Perovskite Solar Cells Containing a Perylene Diimide Cathode Interlayer with a Copper Top Electrode

“…One potential solution is related to the use of copper (Cu) as an alternative to silver and aluminum in cathodes. While Cu provides the cost-effective conductivity and air-stable electrode, the severe energy-level mismatch between the electron transport layer (ETL) and the Cu cathode has a detrimental effect on the charge transfer dynamics. , Furthermore, the interaction between iodine-containing decomposition products and the cathode, leading to the formation of copper iodide, poses a threat to the efficiency and stability of THPSCs. − Consequently, the interfacial properties of the cathode interlayer (CIL) are crucial, and it is essential to optimize the electrical contact and protect against halide/metal diffusion and moisture penetration. − …”