The role of electronic donor moieties in porphyrin dye sensitizers for solar cells: Electronic structures and excitation related properties

Abstract

The development and synthesis of novel dye sensitizers are important for improving the power conversion efficiency of dye-sensitized solar cells (DSSCs) in terms of the role of dye sensitizers in photon to electricity energy conversion processes. How the different moieties tune the electronic structures and related properties is the fundamental issue in designing dye sensitizers. Here, the geometries, electronic structures, excitation properties, and free energy variations for electron injection (EI) and dye regeneration (DR) of porphyrin dye sensitizers SM315, GY50, FA, and KS, containing bulky bis(2′,4′-bis(hexyloxy)-[1,1′-biphenyl]-4-yl)amine, diarylamino group with two hexyl chains, quinolizinoacridine, and triazatruxene as electron donors, respectively, were investigated. The Q bands absorption spectra of FA and KS exhibit a blue-shift relative to those of SM315 and GY50, resulting from weak conjugation effects. The transition configurations and molecular orbital analysis suggest that the electron donors in these dyes are effective chromophores for photon-induced EI in DSSCs. The torsion angle between the electron-donor and the conjugation-bridge has significant effects on electronic structures, excited states, charge transfer (CT) properties, and free energy variations for EI and DR. The transferred charges and CT distances demonstrate that quinolizinoacridine in FA is the most prominent electron donor moiety among these porphyrin dyes.