Wet‐Assisted Annealing Strategy Enables All‐Polymer Solar Cells Efficiency Exceeding 20%

As a promising candidate for flexible and portable photovoltaic devices, all-polymer solar cells (all-PSCs) have recently garnered significant attention in the field of organic photovoltaics. However, due to the unfavorable morphology and weak crystallinity caused by complex chain entanglement within all-polymer systems, the power conversion efficiencies (PCEs) of all-PSCs still lag behind those of small-molecule-acceptor-based organic solar cells. Given that conventional thermal annealing (TA) lacks sufficient control over the crystallization and vertical distribution of polymer acceptors, we developed an innovative wet-assisted annealing (WAA) strategy. By leveraging the selective dissolution and volatilization effects of assist solvents during the thermal annealing process, the vertical distribution of donors and acceptors in bulk heterojunction (BHJ) structures were finely optimized. More importantly, this strategy enhances the molecular stacking of polymer acceptor, and achieves well-defined fibrillar network morphology. Benefiting from this approach, the PM6:PY-DT-based binary all-PSCs achieved a record PCE of 20.04% with enhanced stability, significantly exceeding the performance of conventional TA-processed devices. Meanwhile, the WAA strategy demonstrated consistent effectiveness across different batches of the polymer acceptor, underscoring its robustness and practical value for fabricating high-efficiency and stable all-PSCs.