Porphyrin sensitizers with modified indoline donors for dye-sensitized solar cells

Abstract

As a strong electron donor, indoline has been used in developing organic sensitizers for fabricating efficient dye-sensitized solar cells. Herein we report porphyrin dyes based on modified indoline donors. Firstly, XW29 and XW31 featured with a methylphenyl-substituted indoline and a bulkier dialkylfluorene-substituted indoline, respectively, are synthesized. XW31 exhibits a J_sc of 22.06 mA cm⁻² as compared with that of 21.26 mA cm⁻² for XW29. Consequently, XW31 achieves a higher power conversion efficiency of 10.46% than that of 10.14% for XW29. On this basis, to further broaden the spectral response, a benzothiadiazole (BTD) unit is incorporated as the auxiliary electron acceptor to obtain XW30 and XW32, respectively. The IPCE spectra are thus successfully extended to 850 nm. However, due to possibly aggravated dye aggregation, charge recombination and less effective dye regeneration induced by the BTD unit, moderate efficiencies of ca. 8.6% are obtained. Through coadsorption, elevated efficiencies of ∼9.9% are achieved for XW30 and XW32. These results provide further insights into developing efficient porphyrin dyes by combining the dialkylfluorene moiety with the indoline donor.