High-Performance Ternary Polymer Solar Cells Enabled by Using a Branched Polymer as the Guest Donor

The ternary strategy has been regarded as the most convenient and efficient method to enhance the photovoltaic performance of organic solar cells (OSCs). Here, a slightly branched polymer PM6-B is developed by introducing a 1,3,5-tribromobenzene unit (0.02 equiv) into the preparation process of PM6. The resulting PM6-B exhibits a downshifted HOMO energy level and demonstrates excellent compatibility with PM6. Ternary devices are constructed based on the PM6:N3 host system, in which the branched PM6-B is applied as the guest electron donor. By adding 20 wt % of PM6-B, the ternary device obtains the optimal photovoltaic performance with simultaneously improved open-circuit voltage ( V oc ) of 0.844 V and short-circuit current density ( J sc ) of 27.83 mA cm –2, yielding a significantly increased power conversion efficiency (PCE) of 17.94%. The enhanced performance of the PM6:PM6-B:N3 device is mainly ascribed to facilitated exciton dissociation, improved charge collection, and suppressed charge recombination after the integration of PM6-B. This work demonstrates the potential of using a branched polymer as an isogenous third component to construct high-efficiency ternary OSCs.