The effect of benzoxazole unit on the properties of cyclic thiourea functionalized triphenylamine dye sensitizers

Abstract Two D-π-A-A sensitizers (AZ6-B20 and AZ6-B21) were synthesized by inserting the benzoxazole group as an auxiliary acceptor between the π-linker and the acceptor. And a D-A-π-A sensitizer (AZ6-B19) was also synthesized in our previous works by the insertion of the benzoxazole between the donor and the π-linker. The effects of benzoxazole groups on the properties at different sites of dye sensitizers were distinguishing. Their light harvest abilities were investigated by UV-vis spectra both in the solution and on the films. The results show that the absorption bands of UV-vis spectra are quite different from D-A-π-A and D-π-A-A dyes. The much more intensive molar extinction coefficients (53807 M-1cm-1 and 52555 M-1cm-1) were observed at around 575 nm for D-π-A-A dyes. The photovoltaic properties of DSSCs were also evaluated by J-V curves and IPCE measurements. The results confirmed that D-π-A-A dyes delivered high photovoltaic efficiency (AZ6-B20: 7.48%, AZ6-B21: 8.67%) compared with that of D-A-π-A dye (AZ6-B19: 3.27%). The details on the relation of the structures/properties were discussed by the optical physical absorption, electrical chemical measurements and DFT calculations.