Benzimidazolium salt-based solid-state electrolytes afford efficient quantum-dot sensitized solar cells

Abstract

A novel solid-state electrolyte based on 1,3-dihexylbenzimidazolium ([DHexBIm]) cations combined with Br⁻, BF₄⁻ or SCN⁻ anions is used in CdS/CdSe sensitized quantum dot sensitized solar cells (QDSSCs). A power conversion efficiency of 4.26% was achieved with a fill factor of 56.44% using the [DHexBIm][SCN]-based electrolyte. X-ray powder diffraction analysis reveals that [DHexBIm][SCN] is crystalline with a much higher symmetry than the other two salts. Differential scanning calorimetry and thermal gravimetric analysis of [DHexBIm][SCN] reveals a solid–solid phase transition at 50 °C together with a high thermal stability. Current density–voltage (J–V) tests, Tafel-polarization plots, cyclic voltammetry curves and electrochemical impedance spectroscopic methods were used to characterize QDSSCs and to probe the mechanism of device performance. These studies show that good ionic conductivity and a low R_CE value lead to a good short-current density (J_sc) of 12.58 mA cm⁻², which is the major effect factor for the high power conversion efficiency observed. In the stability test, this device shows excellent long-term stability, maintaining 67% of the initial efficiency after 504 h.