Efficient Semitransparent Organic Solar Cells with CRI over 90% Enabled by an Ultralow‐Bandgap A‐DA'D‐A Small Molecule Acceptor

Abstract Semitransparent organic solar cells (ST‐OSCs) can function as power‐generating windows due to their ability to allow visible light go‐through for human eyesight while absorbing low‐energy photons in the near‐infrared region for photocurrent generation. In this regard, effective ST‐OSCs with high light utilization efficiency (LUE) and color rendering index (CRI) can be developed via a synergistic material and device engineering strategy. Herein, an A‐DA'D‐A acceptor BZO‐4Cl is synthesized with an ultralow optical bandgap of 1.26 eV and bathochromically shifted absorption of roughly 60 nm with respect to Y6. Initially, the opaque devices using PTB7‐Th as the donor show a high power conversion efficiency (PCE) of 14.12% , which can be listed as one of the highest efficiencies for the PTB7‐Th‐based OSCs so far. Then, through these efforts of optimizations in the bulk‐heterojunction(BHJ) composition, top electrodes and anti‐reflection layer, the cutting‐edge ST‐OSC demonstrates a high LUE of 4.02%, and a CRI of 90.67%, making it one of the best‐performing ST‐OSCs with both high LUE and CRI values. These results indicate that the ST‐OSCs presented in this study have significant potential for use in applications that possess transparent visible light and energy‐generation functions.