Synthesis and characterization of nitrogen-doped TiO2 samples and their application as thin film electrodes in dye-sensitized solar cells

Abstract

Dye-sensitized solar cells based on nitrogen-doped nanocrystalline titanium dioxide (TiO2) electrodes have shown improved photovoltaic performance due to the beneficial effects of nitrogen on the electronic and optical properties of TiO2. In this context, we report synthesis, characterization and photoelectrochemical studies of N-doped TiO2 prepared by sol–gel method using methylamine (MA), aniline (A) and furfurylamine (FA) as N dopants. For the comparison, the undoped TiO2 (TiO2–U) was also prepared, keeping all the other experimental conditions identical. The materials obtained have been characterized for optical properties, crystalline structure and surface morphology. The nanocrystalline N-doped TiO2 powders obtained were found to possess different crystallite sizes, surface areas and N-doping levels. When thin films of these TiO2 samples were used as photoanodes in dye-sensitized solar cell (DSSC), taking N719 dye as a sensitizer dye, cell with N-doped (TiO2–A) photoanode showed maximum conversion efficiency with an OCP (V oc) of 0.58 V, current density (J sc) of 1.99 mA cm−2, fill factor (FF) of 0.75 and overall conversion efficiency (η) of 0.86 % under illumination of 100 mW cm−2 light intensity. The maximum incident photon to current conversion efficiency (IPCE) of cell was 75 %, whereas with TiO2–U used as a photoanode and sensitized by N719 dye J sc of 1.61 mA cm−2 could be obtained, demonstrating that the short-circuit photocurrent density of the cell based on N-doped TiO2 electrode increases by more than 20 % compared to the undoped TiO2. Photovoltaic performances were found in the following order: TiO2–A > TiO2–U > TiO2–MA > TiO2–FA.