Unexpected Impact of N-Alkyl Chain Length in Bis-2-cyanoacrylic Acid Substituted Phenothiazines on the Photovoltaic Response of DSSCs

Abstract

The impact of the alkyl chain on the nitrogen atom�N-ethyl, N-butyl, N-octyl, and N-dodecyl�in phenothiazines with bis-2-cyanoacrylic acid units on the optical and electrochemical behavior and finally photovoltaic response of DSSCs sensitized with such dyes was investigated. Such compounds as alternatives to ruthenium-based dyes were evaluated. The optical properties of the phenothiazine derivatives were studied by UV−vis and photoluminescence measurements in various solutions. Additionally, electronic absorption spectra of dyes anchored to TiO 2 were registered. Electrochemical properties were studied by using cyclic and differential pulse voltammetry. Experimental data and the adsorption energies of dyes@TiO 2 were supported by DFT and TD-DFT calculations. DSSCs consisting of a TiO 2 anode sensitized with prepared dyes, I − /I 3 − electrolyte, and Pt/FTO counter electrode were fabricated. The idea of dye cocktail utilization was also developed. The prepared solar cells were characterized via current−voltage, transient absorption, and electrochemical impedance spectroscopy measurements. Transient absorption spectroscopy revealed a positive effect of the alkyl chain length and cocktail dye configuration on the efficiency of the fast electron transfer processes.