New triarylamine sensitizers for high efficiency dye-sensitized solar cells: Recombination kinetics of cobalt(III) complexes at titania/dye interface

Abstract

A new generation of dye-sensitized solar cells (DSCs) is based on a combination of D–π–A organic dyes in conjunction with cobalt-based redox mediators. Here, two new triarylamine organic dyes (M36 and M37) toward cobalt electrolytes are constructed and employed as photosensitizers for dye-sensitized solar cells. The photoelectrochemical properties and photovoltaic performance of dyes are sensitive to the slightly structural modification of the terminal donor in triarylamine. Recombination kinetics of cobalt(III) complexes at titania/dye interface are also studied using electrochemical impedance spectroscopy and controlled intensity modulated photovoltage spectroscopy measurements. Our results show that, for M36 sensitized DSCs, a Marcus inverted region can be reached for the charge recombination kinetics behavior of cobalt(III) species. While that for DSCs based on M37 just lies in the Marcus normal region. The results can be attributed to differences in the retarding charge recombination ability of the dye layer. Benefiting from a Marcus inverted region behavior, the M36 dye exhibits a good compatibility with the [Co(phen)3]2+/3+ redox couples, achieving a high overall power conversion efficiency (PCE) of 9.58% under full sun illumination.