Conventional structure PCE10:EH-IDTBR devices were fabricated after extensive optimisation. A PCE10:EH-IDTBR blend was chosen for its promising PV open circuit voltage (VOC), photocurrent and stability under operation (see chemical structures in Supplementary Fig. ). The OPV cells incorporated a ZnO nanoparticle electron transport layer with a work function of -3.9 eV, which improved charge transfer from the lowest unoccupied molecular orbital (LUMO) of EH-IDTBR to the Ag back electrode (Fig. ). The 23 PV devices with active areas of ~0.25 cm 2 used for this study displayed an average VOC of 1.047±0.003 V, short circuit current density (JSC) of -18.3±1.6 mA cm -2 , fill factor (FF) of 55.9±1.6% and photovoltaic cell efficiency (PCE) of 10.7±0.9% in the reverse scan direction (Supplementary Fig. ). The champion device attained a PCE of 11.8% (Supplementary Fig. ), which is comparable with reported benchmark devices. Cross-section SEM images revealed a multi-layered structure with a ~80 nm thick photoactive layer (see Fig. and EDX elemental mapping in Supplementary Fig. ). UV-vis spectra of the photoactive blend confirmed its strong characteristic absorption in the visible range from 450 to 800 nm (Supplementary Fig. ).