Simultaneous Optimization of Efficiency, Stretchability, and Stability in All-Polymer Solar Cells via Aggregation Control

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.