Understanding Interfacial Recombination Processes in Narrow-Band-Gap Organic Solar Cells

Recombination losses in organic photovoltaics (OPVs) remain aperformance-limiting factor, including bulk trap-assisted recombination and interfacialrecombination at the electrode:active layer interface. In this work, we demonstrate therole of the front electrode:active layer interface in a narrow-band-gap system,PCE10:COTIC-4F, a promising candidate for semitransparent organic photovoltaics.We systematically address charge generation, recombination, and extraction, with afocus on interfacial recombination via surface traps by a comparison of four devicestructures with electrodes based on ZnO, ZnO/PFN-Br, PEDOT:PSS, and a self-dopedconjugated polyelectrolyte (CPE-K). The amount of interfacial recombination isaffected significantly by the electrode choice, while similar levels of bulk recombinationare maintained. For the studied blend, we identify ZnO as a suitable choice, pairing lowsurface recombination rates with beneficial charge carrier generation, favorable energylevel alignment, and efficient extraction. In contrast, PEDOT:PSS-based devices sufferfrom interfacial recombination, which can be suppressed when CPE-K is used instead