Polymerized small molecule acceptors featuring hydrogen-bonded flexible spacers enhance the efficiency and stretchability of organic solar cells

Abstract High power conversion efficiency (PCE) and mechanical robustness are essential for organic solar cells (OSCs) used in wearable electronics. In this paper, we report a polymerized small molecular acceptor, PNH, achieved by incorporating hydrogen-bonding (H-bonding) urea flexible spacers (FS) into a Y5-OD-like polymer backbone. Fourier transform infrared spectroscopy corroborates the formation of strong H-bonding (N-H···O=C) between the carbonyl unit in the donor polymer PBDB-T and the amine group in PNH, as well as within the PNH acceptors. Furthermore, a control Y5-OD polymer (PCO) incorporating a carbonate FS unit, thus incapable of H-bonding with PBDB-T was investigated. Notably, the PBDB-T:PNH blend achieved a power conversion efficiency (PCE) of 12.1% outperforming the PBDB-T:PCO device (10.8%). This improved PCE is attributed to the enhanced molecular aggregation and charge transport induced by H-bonding interactions. Moreover, the introduction of H-bonding via FS incorporation effectively dissipates the strain energy under mechanical deformations. Thus, blend films exhibit an improved crack-onset strain from 12.16% (PBDB-T:PNH) to 18.02% (PBDB-T:PCO). Importantly, intrinsically stretchable OSCs ( is -OSCs) based on the PBDB-T:PNH blend retain 70% of its initial PCE under a 25% strain. Our results highlight the role of incorporating H-bonding FS into the PSMA backbone to enhance both PCE and mechanical stretchability.