Minimizing Interfacial Recombination in 1.8 Ev Triple-Halide Perovskites for 27.2% Efficient All-Perovskite Tandems.

All-perovskite tandem solar cells show great potential to enable highest performances at reasonable costs for a viable market entry in the near future. In particular, wide-bandgap (WBG) perovskites with higher open-circuit voltage (V OC ) are essential to further improve the tandem solar cells' performance. Here, we develop a new 1.8 eV bandgap triple-halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment. With structural analysis, we find that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant Light-Induced Magneto Transport (CLIMAT) measurements were applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady-state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V V OC , reaching 90% of the radiative limit. Combined with a 1.26 eV NBG perovskite with a rubidium iodide additive, this enables a tandem cell with certified efficiency of 27.5%. This article is protected by copyright. All rights reserved.