Semitransparent Organic Solar Cells with Efficiency Surpassing 15%

Abstract Semitransparent organic solar cells (ST‐OSCs) have promising prospects for building or vehicle integrated solar energy harvesting with energy generation and see‐through function. How to achieve both an adequate average visible transmittance (AVT) and high‐power conversion efficiency (PCE) is always the key issue. Herein, a simple but effective strategy for constructing high performance ST‐OSCs by introducing a small molecule [2‐(9‐H‐Carbazol‐9‐yl) ethyl] phosphonic acid (2PACz) into a low‐donor content active layer is reported. The fill factor is improved from 70.5% to 75.5% and correlated to the mitigated charge recombination and strengthened charge extraction, further ascribed to the enhanced build‐in potential, reduced charge transport resistance, and favorable film morphology. By combining the unique nature of 2PACz, that can spontaneously form in situ self‐organized hole transport interlayers under bulk‐heterojunction films, PEDOT‐free ST‐OSCs with a PCE of 15.2%, amongst the highest values in this field, is achieved with an AVT of 19.2%. Moreover, an outstanding light utilization efficiency of 3.39% is also obtained with an AVT of 30.0% and a PCE of 11.3% in a translucent device by tuning the electrode. The work demonstrates a new and simple strategy for achieving excellent AVT and PCE in ST‐OSCs with simplified device structure.