Efficient organic solar cells with small energy losses based on a wide-bandgap trialkylsilyl-substituted donor polymer and a non-fullerene acceptor

Efficient organic solar cells based on a blend of PBDS-T as a donor polymer and BTP-eC9 as non-fullerene acceptor are presented and characterized. PBDS-T is an alternating copolymer that comprises easily accessible electron-rich trialkylsilyl-substituted benzodithiophene and electron-deficient benzodithiophene-4,8-dione units and that can be efficiently and reproducibly synthesized in high molecular weights, while keeping good solubility. PBDS-T exhibits a strong absorption between 450 and 700 nm and combines a wide optical bandgap of 1.86 eV, with low-lying energy levels, and a face-on molecular orientation in thin films. Organic solar cells prepared by blending PBDS-T with BTP-eC9 show considerable performance when as-cast films are annealed in solvent vapor and present a high open-circuit voltage of 0.86 V, a low photon-energy loss of 0.53 eV, and an internal quantum efficiency of 93%. The power conversion efficiency reaches 16.4%, which − to the best of our knowledge − is the highest for a conjugated polymer comprising trialkylsilyl side chains in combination with a Y6-based non-fullerene acceptor. Specifically, the trialkylsilyl side-chains of PBDS-T reduce synthetic complexity, result in a low energy loss by ensuring low energetic disorder, and provide competitive device performance.