| The current state of the art in bulk heterojunction organic solar cells is based on P3HT (poly(3-hexylthiophene)) as donor and PCBM (1-(3-methoxycarbonyl) propyl-l-phenyl[6,61C61), a soluble fullerene derivative, as electron acceptor. The work described in this thesis examines an alternative electron acceptor, C60(CN)2, with higher electron affinity than parent C60, for the first time, for photovoltaic applications. C60(CN)2 thin film material properties such as optical, electrical, structural, composition and morphology were measured so that optimum OPV devices can be designed and fabricated. Solar cell devices were fabricated and solar cell parameters such as open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF), external quantum efficiency (EQE), power conversion efficiency (eta) etc were measured. Field effect electron mobility of C60CN)2 was measured by fabricating P3HT and C60(CN)2 based organic field effect transistors. Ultraviolet photoelectron spectroscopy (UPS) measurements were carried out to understand the charge transfer mechanism and generation of Voc.;Optical properties of C60(CN)2 were found to be comparable to PCBM. An evaluation of electrical properties of C60(CN) 2 and PCBM under similar conditions have shown comparable electron mobilities. The electronic energy levels of C60(CN)2 thin films obtained using UPS measurements indicate that C60(CN)2 has a potential to yield higher Voc. Blending C60(CN) 2 with P3HT resulted in significant fluorescence quenching demonstrating efficient charge transfer between the two materials. Dependence of V oc on the ratio of the two acceptors, C60(CN)2 and PCBM, in the blend was demonstrated for the first time. Morphology can be controlled by controlling the ratio of C60(CN)2 and PCBM in the active layer. C60(CN)2 when blended with PCBM has shown a charge transfer between the two acceptors. It is demonstrated for the first time that C60(CN)2 and PCBM can be used as OPV devices in the ultraviolet region.;Further improvements in the device performance can be achieved by using higher purity material, improved solubility, optimization of thermal annealing process, better control of morphology and using controlled environment. Current work overlay foundation for alternative electron acceptor which may provide higher efficiency with the above suggested improvements. It also allows the opportunity for finding new improved donor-acceptor material systems for enhanced photovoltaic efficiency. |
