Suppressing nongeminate recombination with two well-compatible polymer donors enables 16.6% efficiency all-polymer solar cells

The power conversion efficiency of all-polymer solar cells is rising quickly due to the development of polymerized small molecule acceptors. However, optimizing the active layer morphology remains challenging owing to the long and entangled polymer chains; therefore, the power conversion efficiency still lags behind that of organic solar cells composed of small molecule acceptors. Herein, we adopted a ternary strategy to improve the performance of all-polymer solar cells consisting of PM6:PY-IT by introducing D18-Cl as the third component to fine-tune the nanoscale morphology of the active layer. Because D18-Cl has good compatibility with PM6 and more robust crystalline features, adding D18-Cl regulates the donor and acceptor aggregations in the ternary blend films, leading to stronger crystallinity than the PM6:PY-IT films. Consequently, the ternary devices attained a champion power conversion efficiency of 16.6% (16.5% averaged), outperforming their binary counterparts. The improved performance was associated with enhanced fill factor and short circuit current density, resulting from significantly suppressed nongeminate charge recombination. Our results provide an in-depth understanding of the relationship between the active layer morphology and the nongeminate recombination in the ternary system composed of two well-compatible donors.