Efficient and Stable All‐Polymer Solar Cells Enabled by Dual Working Mechanism

Ternary strategy with integration characteristics and adaptability is a simple and effective method for blooming of the performance of photovoltaic devices. Herein, a novel wideband gap polymer donor PBB2‐Hs is synthesized as the guest component to optimize all‐polymer solar cells (all‐PSCs). High‐energy photon absorption and long exciton lifetime of PBB2‐Hs constitute efficient energy transfer. Good miscibility and cascade energy levels promote the formation of alloy‐like structure between PBB2‐Hs and host system. The dual working mechanisms greatly improve photon capture and charge transfer in active layers. Additionally, the introduction of PBB2‐Hs also optimizes the ordered molecular stacking of acceptors and suppresses molecular peristalsis. Upon adding 15 wt% PBB2‐Hs, the ternary all‐PSC achieved a champion efficiency of 17.66%, and can still maintain 82% photostability (24 h) and 91% storage stability (1000 h) of the original PCE. Moreover, the strong molecular stacking and entanglement between PBB2‐Hs and the host material increased the elongation at break of ternary blend film by 1.6 times (16.2%), allowing the flexible device to maintain 83% of the original efficiency after 800 bends (R = 5 mm). This work highlights the effectiveness of guest polymer on simultaneously improving photovoltaic performance, photostability and mechanical stability in all‐PSCs.