Photovoltaic Properties of Bulk Heterojunction Organic Solar Cell Composed of Coumarin 6 Dye as Light Harvester and Donor Material

The behavior and properties of coumarin 6 (C6) dye as a light harvester and, at the same time, a donor material in combination with a fullerene derivative [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM) acceptor molecule in a new bulk heterojunction (BHJ) solar cell were demonstrated for the first time. The C6:PCBM combination represented a good example of a BHJ blend containing a charge transfer complex (CTC). The formation of a BHJ by blending C6 dye as a donor with PCBM as an acceptor, therefore achieving efficient charge separation and transport throughout the C6:PCBM blend, was verified through the symbatic behavior of the corresponding solar cell. The formation of a CTC in the C6:PCBM blend was indicated from the redshift of the C6 absorption peak after blending with PCBM and verified through the variation in the redshift of the C6 peak with the variation of the C6:PCBM blend composition and, also, through Fourier transform infrared spectroscopy, which revealed additional infrared absorption peaks in the C6:PCBM blend not related to either C6 or PCBM. The formation of a CTC in the C6:PCBM BHJ solar cell assisted in improving the photocurrent and device performance parameters through ultrafast charge separation occurring within the CTC in the blend.