Pyrazolium-based electrolyte for solid-state dye-sensitized solar cells with high fill factor and open-circuit voltage

Abstract

Further development of solid-state dye-sensitized solar cells (ssDSSCs) requires good fill factor as well as high photon to electron conversion efficiency. We synthesized a pyrazolium-based dication organic ionic conductor with good thermal stability and high ionic diffusion coefficient, Py₂C₆. This pyrazolium-based electrolyte for ssDSSC achieves an efficiency of 7.30% with a fill factor of up to 79.6% and an open-circuit voltage of 779 mV, which are superior to the respective parameters reported in the previous literature. The obtained cell was characterized by electrochemical impedance spectra (EIS), cyclic voltammetry (CV) and Tafel plot. The results show 24.43 Ω series resistance and 3.31 kΩ shunt resistance, very close to the values for the device with a frequently used liquid-state electrolyte, and these are the major contributors to the high fill factor. The back reaction of photoelectrons at the TiO₂/electrolyte interface can also be markedly restrained as a result of the large recombination resistance, thus prolonging the electron lifetime. These factors, together with the remarkable catalytic activity of the counter electrode, lead to good photovoltaic parameters of the cell containing Py₂C₆. In stability tests, this device shows excellent long-term stability, maintaining 92% of the initial efficiency after 1000 h.