Interface state recombination in organic solar cells

Recombination in bulk heterojunction organic solar cells based on polycarbazole/fullerene blends are studied through measurements of the solar-cell response. Different recombination mechanisms are analyzed, including recombination of the charge-transfer exciton, Auger recombination, and recombination at interfacial localized states. The measured recombination kinetics, the temperature dependence of the current-voltage characteristics, the dark forward bias diode current, and modeling studies, all indicate that the dominant recombination is through interface states between the polymer and fullerene domains, with an estimated density of order 10^11 cm^-2. Modeling studies indicate that a tenfold reduction in the interface state density could potentially double the solar-cell efficiency.