Simultaneous Optimization of Efficiency, Stretchability, and Stability in <scp>All‐Polymer</scp> Solar Cells via Aggregation Control^†

Comprehensive Summary With the emergence of Y‐series small molecule acceptors, polymerizing the small molecule acceptors with aromatic linker units has attracted significant research attention, which has greatly advanced the photovoltaic performance of all‐polymer solar cells. Despite the rapid increase in efficiency, the unique characteristics ( e. g ., mechanical stretchability and flexibility) of all‐polymer systems were still not thoroughly explored. In this work, we demonstrate an effective approach to simultaneously improve device performance, stability, and mechanical robustness of all‐polymer solar cells by properly suppressing the aggregation and crystallization behaviors of polymerized Y‐series acceptors. Strikingly, when introducing 50 wt% PYF‐IT (a fluorinated version of PY‐IT) into the well‐known PM6:PY‐IT system, the all‐polymer devices delivered an impressive photovoltaic efficiency of 16.6%, significantly higher than that of the control binary cell (15.0%). Compared with the two binary systems, the optimal ternary blend exhibits more efficient charge separation and balanced charge transport accompanying with less recombination. Moreover, a high‐performance 1.0 cm 2 large‐area device of 15% efficiency was demonstrated for the optimized ternary all‐polymer blend, which offered a desirable PCE of 14.5% on flexible substrates and improved mechanical flexibility after bending 1000 cycles. Notably, these are among the best results for 1.0 cm 2 all‐polymer OPVs thus far. This work also heralds a bright future of all‐polymer systems for flexible wearable energy‐harvesting applications.

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