All‐Polymer Semitransparent Organic Solar Cells With Excellent Performance and Enhanced Stability Using Narrow‐Bandgap Terpolymer Donors

ABSTRACT All‐polymer semitransparent organic solar cells (ST‐OSCs), employing narrow‐bandgap (NBG) polymer donor and NBG polymer acceptor for wavelength‐selective light utilization, hold great potential for addressing the trade‐off between efficient light absorption and light transmittance, as well as the stability of devices. Nevertheless, its development has been hindered by the scarcity of high‐performance NBG polymer donors. In this work, through strategic incorporation of a benzodithiophenedione unit into the PCE10 backbone, two NBG terpolymer donors, PS1 and PS2, with deeper energy levels are developed. Importantly, PS2 demonstrates appropriate molecular stacking and crystallinity, and favorable miscibility with the acceptor PY‐IT. Benefiting from the reduced voltage loss due to significantly suppressed non‐radiative recombination loss and the optimal morphology, the opaque PS2:PY‐IT‐based all‐polymer solar cell demonstrates a power conversion efficiency (PCE) of 15.10%. Moreover, the PS2:PY‐IT‐based ST‐OSC achieves an excellent light utilization efficiency (LUE) of 4.19% with PCE of 10.26% and average visible transmittance of 40.84%, which is the highest LUE among all‐polymer ST‐OSCs. This device demonstrates enhanced stability under storage conditions, thermal stress, and light soaking. These results provide guidelines for designing novel NBG polymers and demonstrate that the design of NBG polymers holds immense promise for advancing high‐performance ST‐OSCs.