Light and elevated temperature induced degradation (LeTID) in perovskite solar cells and development of stable semi-transparent cells

Abstract

The stability of perovskite solar cells (PSCs) is one of the major challenges to their commercialization. In this work, the stability of state-of-the-art mesoporous PSCs employing multi-cation mixed-halide perovskite and poly [bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) as the hole-transport-layer (HTL) is studied under illumination at an elevated temperature in N2 environment. The Rb in the quadruple-cation perovskite is found to segregate when the film undergoes aging under simultaneous light and heat exposure. More importantly, the PTAA layer prevents diffusion of gold into the perovskite layer when aged at 85 °C in the dark, but not under light. As a result, the PSCs thermally aged under light degrade much more severely than cells thermally aged in the dark. Therefore, the term Light and elevated Temperature Induced Degradation (LeTID) is introduced for PSCs. The effect is also evident for PCSs employing a copper(II) 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (CuPC) HTL. This effect seriously impacts the operational stability of PSCs and it might not be detected with the current stress tests defined in the IEC-61646 standard. PSCs with a transparent contact and robust perovskite composition are developed with improved stability against LeTID. The cells retain more than 90% of the initial efficiency after > 160 h operating under illumination at 85 °C in N2 environment.