High-performance nonfullerene polymer solar cells with open-circuit voltage over 1 V and energy loss as low as 0.54 eV

In this work, we developed high efficiency nonfullerene PSCs based on a wide bandgap polymer donor PBPD-Th with a structure of meta-alkoxyphenyl benzodithiophene-alt-thienyl benzodithiophene-4,8-dione and a low bandgap small molecule acceptor ITIC. The PBPD-Th shows a strong absorption in the short wavelength of 300-650 nm with a bandgap of 1.91 eV, which is complementary with that of ITIC (1.55 eV). Moreover, PBPD-Th possesses a deep HOMO level of -5.42 eV, which is beneficial to obtain high open-circuit voltage (V-oc) in PSCs. As a result, the optimal PSCs based on PBPD-Th: ITIC showed a power conversion efficiency (PCE) of 10.8% with a V-oc of up to 1.01 V, a high short-circuit current density (J(sc)) of 18.3 mA cm(-2) and a fill factor (FF) of 59%, under the illumination of AM 1.5 G, 100 mW cm(-2). Notably, the energy loss (E-loss) of the optimal PSCs is 0.54 eV, which is smaller than the empirically low threshold of 0.6 eV. The PCE of 10.8% is one of the highest values reported in the literatures for the PSCs with Voc over 1.0 V.