A new small molecule acceptor, Y18, was designed and synthesized. Over 17% efficiency was obtained with single junction solar cells based on Y18.

Recent advances in material design for organic solar cells (OSCs) are primarily focused on developing near-infrared nonfullerene acceptors, typically A-DA′D-A type acceptors (where A abbreviates an electron-withdrawing moiety and D, an electron-donor moiety), to achieve high external quantum efficiency while maintaining low voltage loss. However, the charge transport is still constrained by unfavorable molecular conformations, resulting in high energetic disorder and limiting the device performance. Here, a facile design strategy is reported by introducing the "wing" (alkyl chains) at the terminal of the DA′D central core of the A-DA′D-A type acceptor to achieve a favorable and ordered molecular orientation and therefore facilitate charge carrier transport. Benefitting from the reduced disorder, the electron mobilities could be significantly enhanced for the "wing"-containing molecules. By carefully changing the length of alkyl chains, the mobility of acceptor has been tuned to match with that of donor, leading to a minimized charge imbalance factor and a high fill factor (FF). We further provide useful design strategies for highly efficient OSCs with high FF.

Y14-based single-junction semitransparent inverted OSCs achieved a high power conversion efficiency of 12.67%.

Herein, a new “Y-series” non-fullerene acceptor, Y21, bearing an asymmetric electron-deficient-core (DA′D) and fluorinated dicyanomethylene derivatives as flanking groups, was designed and synthesized for organic solar cell applications.