LAUSR

Metal halide perovskite-based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single-junction counterparts. However, overcoming the significant open-circuit voltage deficit present in wide-bandgap perovskite solar cells remains a major hurdle for realising efficient and stable perovskite tandem cells. Here, we report a holistic approach to overcoming challenges in 1.8 eV perovskites solar cells by engineering the perovskite crystallisation pathway by means of chloride additives. In conjunction with employing a self-assembled monolayer as the hole transport layer, we achieved an open-circuit voltage of 1.25 V and a power conversion efficiency of 17.0%. We elucidate the key role of methylammonium chloride addition in facilitating the growth of a chloride-rich intermediate phase that directs crystallisation of the desired cubic perovskite phase, and induce more effective halide homogenisation. The as-formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic properties. This article is protected by copyright. All rights reserved.