Novel Narrow Bandgap Terpolymer Donors Enables Record Performance for Semitransparent Organic Solar Cells Based on All‐Narrow Bandgap Semiconductors

Abstract Semitransparent organic solar cells (ST‐OSCs) based on all narrow bandgap (all‐NBG) semiconductors are attractive for building integration. Unfortunately, advanced NBG Y‐series acceptors cannot well match with the NBG donors, resulting from their mismatched energy levels and poor compatibility. Herein, a facile terpolymer design strategy is adopted to improve the matching of Y6 with efficient NBG polymer donor PCE10. F or Cl atom functionalized benzodithiophene (BDT) are introduced into the PCE10 matrix to afford two series of terpolymers, namely PCE10‐BDT2F and PCE10‐BDT2Cl. Compared with PCE10, all terpolymers show deeper energy levels, higher extinction coefficients, enhanced face‐on orientation, and better compatibility with Y6. Consequently, significant breakthroughs are achieved for both opaque and semitransparent devices. Particularly, a record power conversion efficiency (PCE) of 13.80% is achieved by PCE10‐BDT2F:Y6‐based device, nearly 40% higher than PCE10:Y6‐based device. ST‐OSCs also achieve impressive PCEs of 12.00% and 10.85% with average visible transmittance (AVT) of 30.98% and 41.08%, respectively, and both PCEs are the highest values with AVT over 30% and 40%. An outstanding light utilization efficiency (LUE) of 4.46% further demonstrates the successful balance of PCE and AVT. These results demonstrate that the design of NBG terpolymers is a facile and highly encouraging strategy for promoting breakthroughs in ST‐OSCs.