All‐Polymer Solar Cells with over 12% Efficiency and a Small Voltage Loss Enabled by a Polymer Acceptor Based on an Extended Fused Ring Core

Abstract Although the field of all‐polymer solar cells (all‐PSCs) has seen rapid progress in device efficiencies during the past few years, there are limited choices of polymer acceptors that exhibit strong absorption in the near‐IR region and achieve high open‐circuit voltage (V_OC) at the same time. In this paper, an all‐PSC device is demonstrated with a 12.06% efficiency based on a new polymer acceptor (named PT‐IDTTIC) that exhibits strong absorption (maximum absorption coefficient: 2.41 × 10⁵ cm⁻¹) and a narrow optical bandgap (1.49 eV). Compared to previously reported polymer acceptors such as those based on the indacenodithiophene (IDT) core, the indacenodithienothiophene (IDTT) core has further extended fused ring, providing the polymer with extended absorption into the near‐IR region and also increases the electron mobility of the polymer. By blending PT‐IDTTIC with the donor polymer, PM6, a high‐efficiency all‐PSC is achieved with a small voltage loss of 0.52 V, without sacrificing J_SC and FF, which demonstrates the great potential of high‐performance all‐PSCs.