Can morphology tailoring improve the open circuit voltage of organic solar cells?

While the effect of interfacial morphology on the short circuit current ( I SC ) of organic photovoltaic devices (OPVs) is well known, its impact on open circuit voltage ( V OC ) and fill-factor ( FF ) are less clear. Since the output power of a solar cell P out = I SC V OC FF , such understanding is critical for designing high-performance, morphology-engineered OPVs. In this letter, we provide an explicit analytical proof that any effort to radically improve V OC by tailoring bulk heterojunction morphology is futile, because any increase in I SC due to larger interface area is counterbalanced by corresponding increase in recombination current, so that the upper limit of V OC BHJ cannot exceed that of the corresponding planar heterojunction devices, i.e., V OC BHJ ≤ V OC PHJ . We discuss the implication of this V OC -constraint on the efficiency optimization of organic solar cells.