Efficient and Mechanically Robust Ultraflexible Organic Solar Cells Based on Mixed Acceptors

Summary Flexible organic solar cells (OSCs) with high power conversion efficiency (PCE) and excellent mechanical properties are considered a promising power source for wearable electronic devices. However, simultaneously achieving high efficiency and robust mechanical stability is still challenging because highly crystalline or aggregated microstructures that are thought to be critical for enabling efficient device operation render the active layer brittle. In this study, we demonstrate 3-μm-thick ultraflexible OSCs by utilizing a mixed fullerene/non-fullerene acceptor that can achieve an efficiency of 13% (certified value of 12.3%) with 97% retention in the PCE after 1,000 bending cycles (bending radius of 0.5 mm). In addition, although ultraflexible OSCs cannot survive under the intrinsic tensile test with a large strain, they exhibit excellent mechanical behavior under the cyclic compression-stretching test via the formation of a buckling device structure, yielding an 89% retention in the PCE after 1,000 cycles (45% compression and bending radius of 10 μm). A facile approach introducing a small amount of high-electron-mobility fullerene acceptor into a non-fullerene binary blend enhances charge transport, improves exciton separation, and optimizes the blend morphology with more amorphous regions, thus producing a more efficient and mechanically robust device.