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

Biswajit Ray, Purdue University - Main Campus
M. S. Lundstrom, Purdue University School of Electrical Engineering
Muhammad A. Alam, Birck Nanotechnology Center, Purdue University

Abstract

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 Pout = I_SCV_OCFF, 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 ISC 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 VOC-constraint on the efficiency optimization of organic solar cells.

Discipline(s)

Electronic Devices and Semiconductor Manufacturing | Polymer Science | Power and Energy