Hydrogen‐Bonding Strategy to Optimize Charge Distribution of PC71BM and Enable a High Efficiency of 12.45% for Organic Solar Cells

Short‐circuit current density (JSC), fill factor (FF), and open‐circuit voltage (VOC) are the determining factors on organic solar cells (OSCs) performance. For ternary blend devices, the VOC generally shows a smaller change compared to their binary blend counterpart. Therefore, increase in the JSC and FF of ternary OSCs is the dominating approach to improve device performance. Here, we report a new strategy to enhance OSCs performance via hydrogen‐bonding between PC71BM and dopant coumarin7 (C7) in a PTB7‐Th:C7:PC71BM ternary system. The formation of hydrogen bonds between PC71BM and C7 was predicted by Vienna ab initio simulations (VASP) and verified by Fourier‐transform infrared spectroscopy (FT‐IR). Hydrogen‐bonding induces charge accumulation on the surface of PC71BM, which facilitates electron withdrawal of PC71BM and π‐π stacking between donor and acceptor, resulting in enhanced JSC values of OSCs. Besides, hydrogen bond interaction improves the morphology of C7‐containing OSCs via formation of an interpenetrating network nanofiber structure, as revealed by transmission electron microscopy (TEM). The combination of the above benefits yields a ternary blend OSC consisting of PTB7‐Th:10%C7:PC71BM to have an average power conversion efficiency (PCE) of 12.23% (maximum PCE of 12.45%) at a JSC of 22.26 mA cm−2 and a FF of 70.71%, which represents 31.89% enhancement above the best PCE of the control OSC (9.44%). These results demonstrate a new strategy to improve OSCs efficiency.