Understanding Interfacial Recombination Processes in Narrow-Band-Gap Organic Solar Cells
Nora Schopp, Hoang Mai Luong, Benjamin R. Luginbuhl, Patchareepond Panoy, Dylan G. Choi, Vinich Promarak, Viktor V. Brus, Thuc‐Quyen Nguyen
Abstract
Recombination losses in organic photovoltaics (OPVs) remain a performance-limiting factor, including bulk trap-assisted recombination and interfacial recombination at the electrode:active layer interface. In this work, we demonstrate the role 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 a focus on interfacial recombination via surface traps by a comparison of four device structures with electrodes based on ZnO, ZnO/PFN-Br, PEDOT:PSS, and a self-doped conjugated polyelectrolyte (CPE-K). The amount of interfacial recombination is affected significantly by the electrode choice, while similar levels of bulk recombination are maintained. For the studied blend, we identify ZnO as a suitable choice, pairing low surface recombination rates with beneficial charge carrier generation, favorable energy level alignment, and efficient extraction. In contrast, PEDOT:PSS-based devices suffer from interfacial recombination, which can be suppressed when CPE-K is used instead.