Alkoxy‐ and Alkyl‐Side‐Chain‐Functionalized Terpolymer Acceptors for All‐Polymer Photovoltaics Delivering High Open‐Circuit Voltages and Efficiencies

Abstract A new terpolymer acceptor is presented, comprising various ratios of the same dithienothienopyrrolobenzothiadiazole (BTP) core with different side chains—alkoxy side chains (BTPO‐IC) and alkyl side chains (BTP‐IC)—and thiophene units, for use in all‐polymer organic photovoltaics. Devices incorporating binary blends of this terpolymer and the polymer PM6 as the active layer displayed open‐circuit voltages ( V OC ) that increase linearly upon increasing the molar ratio of BTPO‐IC. For example, the optimized device incorporating PM6:PY‐0.2OBO (i.e., with 20 mol% of BTPO‐IC) (1:1.2 wt.%) blend, with the smallest domain sizes but largest coherence length and combined face‐on and edge‐on orientation fractions among all blends, have a champion power conversion efficiency (PCE) of 16.7% ( V OC = 0.97 V; J SC = 25.2 mA cm −2 ; FF = 0.68), whereas the device containing a similar blend ratio of the PM6:PY‐OD:PY‐OBO ternary blend (1:0.96:0.24 wt.%) displayed a PCE of 8.6% ( V OC = 0.969 V; J SC = 18.7 mA cm −2 ; FF = 0.48). The device with PM6:PY‐0.2OBO displays better thermal stability than the devices with PM6: PY‐OD or PY‐OBO. Thus, employing terpolymer acceptors with differently functionalized side‐chain units can be an effective approach for simultaneously optimizing the aggregation domain and enhancing the PCEs and thermal stabilities of all‐polymer devices.