4,4-Difluoro-Boradiazaindacene-Based Terpolymer Donors for Semitransparent Organic Solar Cells with Balanced Efficiency and Transparency

Semitransparent organic solar cells (ST-OSCs), which combine the dual advantages of photoelectric effect and optical transparency, hold great promise for integration into buildings and electronic devices. Photoactive layer materials that exhibit both high power conversion efficiency (PCE) and average visible transmittance (AVT) are highly desirable for ST-OSCs, yet their molecular design remains a major challenge. In this work, we develop a rational donor design strategy by embedding the 4,4-difluoro-boradiazaindacene (BODIPY)-based acceptor unit TBDZ into the classical polymer donor PCE10, thereby achieving an improved balance between the PCE and AVT in ST-OSCs. The incorporation of the TBDZ unit significantly regulates the molecular configuration and electron delocalization of PCE10 and, thus, its physicochemical and photoelectric properties. In particular, the PCE10-TBDZ-5%-based opaque OSC demonstrates more efficient exciton dissociation, faster charge transport, and suppressed energy loss, thus yielding a much higher PCE of 11.73% compared to that of the PCE10-based device (PCE = 9.75%). Furthermore, the reduced visible light absorption coefficient of PCE10-TBDZ-5% relative to that of PCE10 enables the corresponding ST-OSC to achieve improved AVT while maintaining superior photovoltaic performance. As a result, compared with the PCE10-based ST-OSC with a light utilization efficiency (LUE) of 3.00%, the PCE10-TBDZ-5%-based ST-OSC yields a significantly improved LUE of 3.93%, which ranks among the highest values for ST-OSCs without the application of additional optical coatings.