Electron-deficient fused dithieno-benzothiadiazole-bridged polymer acceptors for high-efficiency all-polymer solar cells with low energy loss

A pair of A₁-A₂-type polymer acceptors (PY-DTBT and PY-DT-BT) including acceptor backbones (A₁) with fused- or unfused-electron-deficient linkers dithieno-benzothiadiazole (DTBT) or DT-BT (A₂), and corresponding comparative polymer acceptor PY-IT are synthesized for all-PSCs, respectively. PY-DTBT and PY-DT-BT neat film exhibit slightly blue-shifted absorption but higher absorption coefficients, and slightly down-shifted energy levels compared to PY-IT. Moreover, PY-DTBT exhibits a more rigid backbone with tighter interchain packing compared to PY-IT and PY-DT-BT, thus achieving better electron-transport in neat films. The PM6/PY-DTBT films possess well-distributed fibril network morphology with suitable phase segregation and better face-on crystallization, which can promote charge generation and extraction, and better-balanced charge mobilities in corresponding all-PSCs. Consequently, the PM6/PY-DTBT LBL-processed all-PSCs produce a top-ranked PCE of 17.58 % with a small energy loss (E_loss) of 0.51 eV, which is obviously higher than that of PM6/PY-IT (16.84 %) and PM6/PY-DT-BT (13.24 %). Furthermore, the all-PSCs based on PM6/(PY-DTBT_{90 %}:PY-IT_{10 %}) achieved a champion PCE of 18.5 % with remarkable FF, which is the one of highest reported value for the electron-deficient linker-based PSMAs in all-PSCs. This work demonstrates that employing DTBT as electron-deficient fused-ring linkage paves the way to achieve excellent polymer acceptors for further improving the efficiency of all-PSCs with small E_loss simultaneously.