Effect of electron-deficient linkers on the physical and photovoltaic properties of dithienopyrrole-based organic dyes

Organic sensitizers containing dithienopyrrole donor, benzotriazole or quinoxaline in the conjugation pathway, and cyanoacrylic acid acceptor featured in a donor–acceptor-π–acceptor configuration are reported. The effect of the nature of different conjugating bridges on photophysical, electrochemical and photovoltaic properties was systematically evaluated. The incorporation auxiliary acceptors broadened the absorption spectra and modulated the excited state energy levels. The DFT calculation unraveled a significant overlap of HOMO and LUMO orbitals in benzotriazole-containing dyes and the charge transfer character for the longer wavelength absorption. Among the dyes, a dye containing benzotriazole and thiophene in the conjugation pathway exhibited highest power conversion efficiency attributable to efficient electron injection and pronounced inhibition of electron recombination.