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

Two D-pi-A-A sensitizers (AZ6-B20 and AZ6-B21) were synthesized by inserting the benzoxazole group as an auxiliary acceptor between the pi-linker and the acceptor. And a D-A-pi-A sensitizer (AZ6-B19) was also synthesized in our previous works by the insertion of the benzoxazole between the donor and the pi-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-pi-A and D-pi-A-A dyes. The much more intensive molar extinction coefficients (53807 M-1 cm(-1) and 52555 M-1 cm(-1)) were observed at around 575 nm for D-pi-A-A dyes. The photovoltaic properties of DSSCs were also evaluated by J-V curves and IPCE measurements. The results confirmed that D-pi-A-A dyes delivered high photovoltaic efficiency (AZ6-B20: 7.48%, AZ6-B21: 8.67%) compared with that of D-A-pi-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.

Automated summary

The study investigated the effects of benzoxazole groups at different positions on the properties of dye sensitizers. It was found that D-pi-A-A dyes showed superior light absorption and photovoltaic efficiency compared to D-A-pi-A dyes.