New Random Copolymer Acceptors Enable Additive-Free Processing of 10.1% Efficient All-Polymer Solar Cells with Near-Unity Internal Quantum Efficiency

Finding effective molecular design strategies to optimize the active layer blend morphology is among the long-standing challenges in developing efficient all-polymer solar cells (all-PSCs). Here we show that new biselenophene/selenophene-linked naphthalene diimide random copolymer acceptors BSSx (x = 10, 20, 50) facilitate the achievement of high-performance all-PSCs without the use of any solution processing additive. Blends of BSS10 with donor polymer PBDB-T combined 10.1% power conversion efficiency with 97% internal quantum efficiency and 0.59 eV optical band gap energy loss (Eloss). BSS10- and BSS20-based devices have the best combination of high external quantum efficiency (>85%) and small Eloss (<0.6 eV) among all-PSCs yet reported. The results demonstrate that the blend morphology, charge carrier mobilities, and photovoltaic properties of all-PSCs could be rationally optimized by means of a synthetic variable—the random copolymer composition.