High-performance nonfullerene polymer solar cells based on a fluorinated wide bandgap copolymer with a high open-circuit voltage of 1.04 v

In this work, efficient nonfullerene (NF) polymer solar cells (PSCs) based on a polymer donor PM6 containing a fluorinated-thienyl benzodithiophene unit and a small molecule acceptor ITIC were developed. PM6 possesses a strong absorption in the short wavelength region of 300-685 nm with a large bandgap of 1.80 eV, which is complementary to that of ITIC (1.55 eV) and facilitates achieving high short-circuit current (J_sc) in PSCs. Moreover, PM6 shows a deep HOMO level of -5.50 eV, a strong crystallinity and a dominant face on packing, which helps to achieve a high open-circuit voltage (V_oc) and fill factor (FF) in PSCs. As a result, the PM6:ITIC-based PSCs obtained a power conversion efficiency (PCE) of 9.7% with a V_oc of up to 1.04 V, a J_sc of 16.0 mA cm^-2 and a FF of 58%, under the illumination of AM 1.5G, 100 mW cm^-2. Notably, the energy loss (E_loss) of the PSCs is as low as 0.51 eV, which is smaller than the empirically low threshold of 0.6 eV. The PCE of 9.7% is one of the highest values reported in the literature for PSCs with a V_oc over 1.0 V and an E_loss less than 0.55 eV.