Electronic properties and open-circuit voltage enhancement in mixed copper phthalocyanine:fullerene bulk heterojunction photovoltaic devices

Ng, T. W.; Lo, M. F.; Fung, M. K.; Lai, S. L.; Liu, Z. T.; Lee, C. S.; Lee, S. T.
November 2009
Applied Physics Letters;11/16/2009, Vol. 95 Issue 20, p203303
Academic Journal
While bulk heterojunctions (HJ) have been used in organic photovoltaic (OPV) devices, there are few studies on their interface electronics and mechanisms on device performance. Here, we studied the electronic structure of a mixed CuPc:C60 and a discrete CuPc/C60 junctions using photoemission spectroscopy. The HOMOCuPc-LUMOC60 energy offset, which controls the theoretical maximum open-circuit voltage (Voc), was increased from 0.64 to 1.13 eV by mixing CuPc with C60. This Voc increase is attributed to the underlying substrate work function and charge transfer between two molecules. The results provide an understanding of the Voc enhancement in OPV devices with bulk HJ.


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