Record Performance Unlocked by Tailored Polymer Donors in All‐Narrow‐Bandgap Semitransparent Organic Solar Cells

ABSTRACT All‐narrow‐bandgap (all‐NBG) semitransparent organic solar cells (ST‐OSCs) typically suffer from much higher energy loss ( E loss ) and unfavorable photoactive layer morphology, thus leading to inferior power conversion efficiency (PCE) and light utilization efficiency (LUE). Herein, a series of NBG polymers are rationally designed and synthesized, aiming to optimize the donor‐acceptor matching and thereby enhance the performance for all‐NBG devices. Benefiting from the down‐shifted energy level and improved compatibility, the PS5‐based opaque devices yield a record‐breaking PCE of 16.31% among all‐NBG OSCs, with a much lower E loss of 0.543 eV. Furthermore, by optimizing the top transparent electrode, the ST‐OSCs based on PS5 deliver a PCE of 12.36% while maintaining an average visible transmittance (AVT) of 42.88%, thereby achieving a remarkable light utilization efficiency (LUE) of 5.30%, which is the highest value reported to data for all‐NBG ST‐OSCs. This study enriches the family of NBG polymers and, more importantly, proposes highly instructive insights for the molecular design strategy of high‐performance NBG polymer materials.