Enhanced hole selecting behavior of WO3 interlayers for efficient indoor organic photovoltaics with high fill-factor

To optimize the indoor performance of organic photovoltaics (OPVs) with minimized surface recombination, using the appropriate hole-collecting interlayer (HCI) is particularly important because the number of generated charges is much smaller than that under 1-sun condition. In this study, we developed efficient indoor OPVs based on a poly(3-hexylthiophene): indene-C-60 bisadduct photoactive layer by incorporating solution-processed tungsten oxide (WO3) as the HCI. The performance of the developed OPVs was compared with that of reference OPVs employing a poly(3,4-ethylenedioxythiophene): poly(styrene-sulfonic acid) (PEDOT: PSS) HCI. The new OPVs with WO3 HCIs exhibited an average power-conversion efficiency (PCE) of 13.0% +/- 0.3% under a 1000 lx light-emitting diode, which was slightly higher than the PCE of reference OPVs (12.7% +/- 0.2%). The superior indoor performance of WO3 HCI-based OPVs can be attributed to their more effective hole-collecting and electron-blocking properties associated with the higher work function and lower electron affinity of WO3 when compared to PEDOT: PSS; these features result in an excellent fill factor (similar to 75%) and a high open-circuit voltage (similar to 0.71 V) for WO3 HCI-based OPVs. These results demonstrate that inexpensive low temperature-processed WO3 HCIs can be excellent candidates in OPVs for indoor applications.