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Schematic semiconductor energy diagram showing bimolecular recombination in pristine semiconductors (a) and in bulk heterojunction solar cells (b). Due to the energy barrier at the donor/acceptor interface, the charge carriers are confined to two different materials.
Simulated current-voltage characteristics of a bulk heterojunction photovoltaic device. The solid line corresponds to the recombination constant of Eq. (3), while the dashed line denotes the result for Eq. (4), i.e., taking only the slowest charge carrier into account. The maximum obtainable FF would be 84%, corresponding to no recombination (dotted line). The FF corresponds to the ratio of the area of the shaded rectangle (maximum power) to the area of the outer rectangle defined by and .
Current-voltage characteristics normalized to the short-circuit current (symbols) of two P3HT/PCBM solar cells annealed at 52 °C (a) and 70 °C (b). The solid lines denote simulations using Eq. (4), while the dashed lines correspond to simulations using Eq. (3).
The experimental FF (symbols) as a function of the mobility ratio. The solid line denotes simulations using Eq. (4), while the dashed line corresponds to simulations using Eq. (3).
Overview of experimentally determined mobilities, parameters used in the fits to the data of Fig. 3, and corresponding FFs.
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