Surface recombination in organic solar cells: Intrinsic vs. doped active layer

This study extends the analytical model of surface recombination in organic solar cells with an intrinsic active bulk-heterojunction layer. The key finding of the developed multi-mechanism recombination model accounting for the intrinsic active layer is that the slope of V OC vs. ln(Light Intensity) cannot be lower than 1.0 kT/q even at the extremely high concentrations of surface traps. We revealed the difference in recombination-related parameters determined in the scope of the multi-mechanism recombination model for the doped or intrinsic active layer and highlighted the importance of identifying the doping level of the active layer material. This is demonstrated by a synergy of comprehensive simulation and experimental analysis of organic solar cells with donor: acceptor blends: (PM6:Y6, PTB7-Th:COTIC-4F, PTB7-Th:O-IDTBR and PTB7-Th:ITIC-4F).