Influence of the auxiliary acceptor and π-bridge in carbazole dyes on photovoltaic properties

Six N-dimethylfluorenylcarbazole dyes have been synthesized based on benzene, furan and thiophene π-bridge with or without benzothiadiazole auxiliary acceptor. Their photophysical properties and photovoltaic performance are investigated systematically based on the incorporation of benzothiadiazole and the variety of π-bridges. The presence of benzothiadiazole broadens the absorption spectra and favors the light-harvesting abilities, which benefits better IPCE spectra and accordingly improved JSC. In addition, benzothiadiazole plays a role on the effects of π-bridge on the photoelectrical conversion efficiency. Dye bearing thiophene bridge achieves optimal photovoltaic performance 4.14% among those carbazole dyes without benzothiadiazole while when with benzothiadiazole dye bearing furan bridge exhibits the best cell efficiency 4.96% under AM 1.5G condition (N719 dye's 6.57% under the same condition).