Balancing bandgap and charge transport in triple-cation perovskite for efficient indoor photovoltaics

The tunable bandgaps of metal halide perovskites lead to their promising application in indoor photovoltaics (IPVs). However, perovskites with wide bandgaps suitable for indoor light typically have lower conductivity and higher defect density, which leads to inefficient charge transport and extraction, limiting their photovoltaic performances. Herein, we investigated the IPV characteristics of triple-cation perovskites with varying bandgaps by tailoring the Br/I ratios. We found that wide-bandgap perovskites could effectively utilize indoor light and achieve high open circuit voltage values under low illumination conditions. However, increasing the Br/I ratios results in higher defect density, leading to decreased short-circuit current density and fill factor. We thoroughly studied the crystallization dynamics, defect density, and charge transfer properties of triple-cation perovskites with varying bandgaps. We found the prevailing concept that efficient IPVs taking the bandgap of IPV materials into special consideration was not comprehensive. We demonstrate that IPV devices with superior IPV properties can be developed by appropriately reducing the Br contents in wide-bandgap crystals. In other words, the preparation of IPV crystal materials should consider both the bandgap and charge transport characteristics. In this work, we obtained devices with the optimal efficiency of 40.71% under 1035 lux LED illumination by achieving a balance between bandgap and charge transfer (Br 0.23, 1.62 eV). This research provides valuable insights for the design of efficient IPVs.