Rigid triarylamine donor-π-acceptor porphyrin dyes and their application in dye-sensitized solar cells

Three donor-π-acceptor porphyrin dyes bearing a variety of rigid triarylamine donor groups were synthesized for application as photosensitizers in TiO₂ based dye-sensitized solar cells (DSSCs). Compared with the "naked" porphyrin ZnP, i.e. having no triarylamine moiety, broadened and red-shifted spectral features were exhibited by the triaylamine porphyrin sensitizers ISB-ZnP, CZ-ZnP, and IDB-ZnP where ISB = 5-phenyliminostilbene, CZ = 5-phenylcarbazole, and IDB = 5-phenyliminodibenzyl. Percentage power conversion efficiencies (η) and incident photon-to-current conversion efficiencies (%IPCE) in DSSC devices show the trend ISB-ZnP < ZnP < CZ-ZnP < IDB-ZnP. Inferior performance of the ISB-ZnP dye is attributed to its weaker adsorption to the TiO₂ film, which is roughly half that of ZnP. In contrast, introduction of the CZ and IDB electron donors is demonstrated to promote a better performance than the "naked" ZnP porphyrin. The best performance was observed for the IDB-ZnP device reaching a power conversion efficiency of η = 3.62% under AM 1.5 irradiation conditions with a corresponding %IPCE maximizing at 48% for both Soret band (450 nm) and Q band (570 nm) photoexcitation.