Leveraging donor–acceptor mutual dilution to finely tune vertical phase separation for high-performance semitransparent organic solar cells

Abstract

Organic semiconductors hold significant potential for building-integrated photovoltaics due to their ability to selectively absorb near-infrared and ultraviolet light while transmitting visible light. However, concurrently achieving high power conversion efficiency (PCE) and average visible transmittance (AVT) in semitransparent organic solar cells (ST-OSCs) remains challenging. This trade-off is particularly prominent in ST-OSCs based on all narrow-bandgap (NBG) material systems, which can ensure high transparency but usually suffer from morphological defects. Although the layer-by-layer (LBL) technique can improve vertical phase separation, it often leads to an insufficient donor/acceptor (D/A) interpenetration region, which restricts the improvement of photovoltaic performance. Herein, to address the morphological challenges in all-NBG systems, we adopt a donor–acceptor mutual dilution strategy integrated with the LBL process to fabricate mutually diluted heterojunctions, which aims to enhance the vertical composition gradient and expand the D/A interpenetration region, thereby promoting exciton dissociation and charge transport. Consequently, the mutually diluted opaque device M-PCE10-2F/M-Y6 achieves a PCE of 14.98%, which is higher than that of the undiluted device PCE10-2F/Y6 (14.15%) and the single-layer diluted devices (14.47% for M-PCE10-2F/Y6 and 14.63% for PCE10-2F/M-Y6). Meanwhile, the mutually diluted ST-OSC achieves a remarkably balanced PCE and AVT, yielding the highest light utilization efficiency (LUE) of 4.90%. In addition, the mutually diluted device also demonstrates enhanced stability and effective thermal insulation, highlighting the promise of the mutually diluted strategy for advancing high-performance and multifunctional ST-OSCs.