Blended bismuth-based Cs3 Bi2 I9 /Ag2 BiI5 perovskite films incorporated potassium iodide for high-efficiency carbon electrode solar cells

Abstract

Abstract Bismuth-based lead-free perovskite solar cells (PSCs) are a non-toxic alternative to lead-based organic-inorganic hybrid PSCs. However, bismuth-based halides PSCs exhibit low power conversion efficiency (PCE) due to the grain boundaries and interfacial defects in the crystalline perovskite film. This discouragingly poor PCE has limited the continued development of bismuth-based PSCs. Herein, for the first time on record, this work fabricated blended, heterojunction, all-inorganic bismuth-based PSCs consisting of Cs3Bi2I9 and Ag2BiI5 perovskite absorber layer components with potassium iodide (KI) incorporation and carbon electrodes. Scanning Electron Microscopy (SEM) and X-ray diffraction spectroscopy (XRD) techniques confirmed that the addition of KI enhances the perovskite’s surface morphology, leading to larger grains and a more uniform distribution of contact potential along the grain boundaries. The Cs3Bi2I9/Ag2BiI5 PSC device with KI incorporation (K-C-ABI) achieved a record PCE of 8.82% and an extraordinary open-circuit voltage of 0.82 V. This record-breaking photovoltaic performance can be traced to the improved grain size of the Cs3Bi2I9/Ag2BiI5 PSCs and effective passivation of the grain boundaries and interfacial defects by KI. These crystallographic phenomena synergistically promoted exciton separation, thus the unprecedented photovoltaic performance. The K-C-ABI device also exhibited comparatively high stability, retaining ~98 % of the initial PCE after 150 days of exposure to ambient conditions (RH: 20–30%, room). The present findings support the results in preceding publications on the potential to enhance the efficiency of all-inorganic PSCs by blending different perovskite precursor solutions. Therefore, this study has effectively demonstrated defect passivation via KI incorporation for high-efficiency lead-free Bi-based PSCs.