Effect of Nb Doping of TiO2 Electrode on Charge Transport in Dye-Sensitized Solar Cells

Abstract

Dye-sensitized solar cells (DSCs) can be regarded as third-generation photovoltaic devices which have low fabrication costs and high photovoltaic performance. The efficiency of DSCs is influenced by the electron transport within the TiO2-dye-electrolyte system and can be improved by modifying the TiO2 electrode with Nb doping. DSCs with Nb-doped and undoped TiO2 electrodes were fabricated and investigated. The Nb-doped TiO2 layers were prepared by a sol-gel method followed by hydrothermal treatment with an Nb content ranging from 0.7 to 3.5 mol%. The obtained layers were characterized using XRD, SEM, TEM, and low temperature PL measurements. Electrical impedance spectroscopy was used to study the electronic transport at the TiO2-electrolyte interface. The electron lifetime, was found to increase from 8 ms for DSCs with undoped TiO2 layers to 26 ms for cells based on TiO2 electrodes doped with 2.7 mol% of Nb. The increase in the electron lifetime correlates with a rise in the short circuit current (Jsc). Nb doping concentrations lower than 1.7 mol% increase the resistance at the TiO2-electrolyte interface and consequently increase the value of the open circuit voltage (Voc). Doping with 1.7 mol% of Nb increases the both Jsc and Voc values and significantly improves the device efficiency.