Fabrication of Phase-Separated Benzoporphycene/[6,6]-Phenyl-C61-Butyric Acid Methyl Ester Films for Use in Organic Photovoltaic Cells

The crystallization behavior of benzoporphycene (BPc) converted from a thermoconvertible BPc precursor (BPc-pre) in the presence of [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) was investigated. Upon annealing spin-coated films of BPc-pre and PCBM, BPc and PCBM crystallized individually to form a phase-separated structure. Repeated spin-coating of BPc-pre and PCBM in dichloromethane solution and subsequent annealing allowed the thickness of BPc films to be increased. BPc crystallized homoepitaxially on the underlying crystalline BPc layer after each deposition step. The thermal conversion conditions affected the size of BPc and PCBM crystals and the photovoltaic properties of the corresponding cells. An organic photovoltaic cell containing a repeatedly stacked BPc/PCBM film prepared by annealing at 250 °C for 1 min showed good rectification and a power conversion efficiency of 0.16%.