Theoretical studies of electronic and optical properties of the triphenylamine-based organic dyes with diketopyrrolopyrrole chromophore

A series of organic donor-pi-acceptor dyes with difference in pi spacer have been designed and investigated theoretically as sensitizers for application in dye-sensitized solar cells. Density functional theory and time-dependent density functional theory calculations reveal how the additional electron-withdrawing diketopyrrolopyrrole unit and pi spacer order influence the physical properties of the dyes, including spectral response, light harvesting efficiency, and electron injection rate. The results show that auxiliary acceptor leads to the greatly red-shifted of the charge-transfer absorption band. Meanwhile, the number and sort order of thiophene groups can significantly tune the orbital energy levels and change the electronic transition processes. The thiophene groups locating between triphenylamine and diketopyrrolopyrrole units would conduce to the light absorption and electron injection efficiency. The results also suggest that the donor-acceptor-pi-acceptor type dyes have indirect electron injection mode compared with the direct mode in the dyes without containing diketopyrrolopyrrole. (C) 2014 Elsevier Ltd. All rights reserved.