Influence of charge accumulation of photogenerated carriers in the vicinity of donor/acceptor interface on the open-circuit voltage of zinc-porphyrin/C60 heterojunction organic photovoltaic cells

The correlation between open-circuit voltage (V-OC) and built-in potential (V-bi) upon photo-irradiation in the vicinity of the donor/acceptor (D/A) interface in zinc-octaethylporphyrin [Zn(OEP)]/C-60 heterojunction photovoltaic (OPV) cells is investigated by examining the capacitance-voltage (C-V) characteristics. Charge accumulation of photogenerated carriers in the vicinity of the D/A interface is found to enlarge V-bi of both D [Zn(OEP)] and A (C-60) films in the vicinity of the interface. In addition, it is noted that V-OC is in good agreement with the sum of V-bi of each film in the vicinity of the D/A interface. This suggests that charge accumulation of photogenerated carriers in the vicinity of the D/A interface plays a key role in determining V-OC for solar cells.