Br Vacancy Defects Healed Perovskite Indoor Photovoltaic Modules with Certified Power Conversion Efficiency Exceeding 36%

Abstract Indoor photovoltaics (IPVs) are expected to power the Internet of Things ecosystem, which is attracting ever‐increasing attention as part of the rapidly developing distributed communications and electronics technology. The power conversion efficiency of IPVs strongly depends on the match between typical indoor light spectra and the band gap of the light absorbing layer. Therefore, band‐gap tunable materials, such as metal‐halide perovskites, are specifically promising candidates for approaching the indoor illumination efficiency limit of ∼56%. However, perovskite materials with ideal band gap for indoor application generally contain high bromine (Br) contents, causing inferior open‐circuit voltage (VOC). By fabricating a series of wide‐bandgap perovskites (Cs0.17FA0.83PbI3−xBrx, 0.6 ≤ x ≤ 1.6) with varying Br contents and related band gaps, it is found that, the high Br vacancy (VBr) defect density is a significant reason that leading to large VOC deficits apart from the well‐accepted halide segregation. The introduction of I‐rich alkali metal small‐molecule compounds is demonstrated to suppress the VBr and increase the VOC of perovskite IPVs up to 1.05 V under 1000 lux light‐emitting diode illumination, one of the highest VOC values reported so far. More importantly, the modules are sent for independent certification and have gained a record efficiency of 36.36%.