From binary to quaternary: high-tolerance of multi-acceptors enables development of efficient polymer solar cells

For optimum coverage of the optical spectrum and further enhancement of the carrier transport, ternary and even more multi-composition strategies have been universally explored. As PC71BM and PC61BM are both compatible with PTB7-Th and IEICO-4F takes advantage of optical absorption in the near-infrared region, we combined PTB7-Th:IEICO-4F:PC71BM:PC61BM quaternary compositions to fabricate high-efficiency polymer solar cells (PSCs) with good tolerance ratios of the fullerene acceptors. After blending the fullerene alloys PC71BM and PC61BM into the host PTB7-Th:IEICO-4F system, the optical response in the whole wavelength regime has been strengthened with significantly enhanced electron mobility. Concomitantly, the short-circuit current density (J(sc)) surged from 22.07 to 24.37 mA cm(-2) and the fill factor (FF) ascended from 58.24% to 69.30%, which finally resulted in a champion power conversion efficiency (PCE) of 12.52%, which is much higher than that of the binary control device (9.67%). This significant improvement is attributed to the fine-tuning of the morphology of the photo-active layer and feasible carrier transport. Interestingly, this finding implicates the synergistic effect of PC71BM and PC61BM to successfully enhancing the carrier transport. In addition, it demonstrates a broad tolerance of the acceptor proportions, resulting in higher PCE values for the quaternary devices as compared to the ternary devices. Lastly, generality for other systems evidences and provides guidelines for quaternary strategy utilization. Thus, the simplicity of quaternary strategies could be greatly beneficial to not yet elaborate commercial processes.