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

Automated summary

This study demonstrates the role of the front electrode:active layer interface in organic photovoltaics. The amount of interfacial recombination is significantly affected by the choice of electrode, while similar levels of bulk recombination are maintained. ZnO is identified as a suitable choice, pairing low surface recombination rates with beneficial charge carrier generation, favorable energy level alignment, and efficient extraction. On the other hand, PEDOT:PSS-based devices suffer from interfacial recombination, which can be suppressed by using a self-doped conjugated polyelectrolyte (CPE-K) instead.