Highly Efficient Indoor Perovskite Solar Cells with 40% Efficiency Using Perylene Diimide‐Based Zwitterionic Cathode Interlayers

Metal halide perovskites are ideal candidates for indoor photovoltaics (IPVs) due to their tunable bandgaps, which allow the active layers to be optimized for artificial light sources. However, significant non-radiative carrier recombination under low-light conditions has limited the full potential of perovskite-based IPVs. To address this challenge, an integration of perylene diimide (PDI)-based sulfobetaines as cathode interlayers (CILs) is proposed and the impact of varying alkyl chain length (from 1,2-ethylene to 1,5-pentylene) between the cationic and the anionic moieties is examined. The respective four PDI materials are synthesized almost qualitatively using a one-step microwave-assisted process. All of them show adequate thermal stability and energy levels suitable for the desired application as CILs. Moreover, their degradation temperature, LUMO level, conductivity, and performance in model devices are found to change positively along with the alkyl chain length increase. Among the tested derivatives, the compound equipped with the longest alkyl chain (PDI-C5-S3) stands out for its superior electrical conductivity and enhanced ability to lower the silver cathode work function. When incorporated into Cs_0.18FA_0.82Pb(I_0.8Br_0.2)-based wide-bandgap perovskite solar cells (PSCs), the PDI-C5-S3 interlayer lead to an outstanding power conversion efficiency (PCE) of 19.04% under one-sun illumination and a remarkable 40.72% under 3000K LED (1000 lux) conditions.