Highly efficient ternary polymer solar cells by optimizing photon harvesting and charge carrier transport

Ternary strategy exhibits some apparent advantages to improve the performance of polymer solar cells (PSCs), such as using two donors or two acceptors to enhance photon harvesting and maintain the simple cell fabrication process. The power conversion efficiency (PCE) of PSCs was increased from 4.89% to 5.54% by doping 4 wt% SMPV1 into Si-PCPDTBT:PC₇₁BM binary system. The PCE improvement should be attributed to the enhanced photon harvesting in the visible light range and optimized charge carrier transport by doping appropriate SMPV1 in the active layers. The champion PCE values were also increased from 4.89% to 5.73% or from 5.54% to 6.44% for binary or the optimized ternary PSCs by CHCl₃ solvent vapor annealing treatment. The positive effect of appropriate SMPV1 doping ratio should be attributed to the efficient energy transfer from SMPV1 to Si-PCPDTBT and the more balanced charge carrier transport in the ternary active layers. The energy transfer from SMPV1 to Si-PCPDTBT can be clearly confirmed from the absorption, photoluminescence (PL) spectra and time-resolved transient PL spectra of pure and blend films. The more balanced charge carrier transport can be further demonstrated from the corresponding hole-only and electron-only devices.