Crystal structure, optical and electrical characteristics of rutile $$\hbox {TiO}_{2}$$ nanocrystallite-based photoanodes doped with $$\hbox {GeO}_{2}$$

Abstract

The effect of germanium dioxide, GeO 2 doping on dye-sensitized solar cell (DSSC) TiO 2 nanocrystallite photoanodes with composition (TiO 2-(GeO 2) x : 0 ≤ x ≤ 0.3 wt%) has been studied. The pure sample and GeO 2-doped samples have been synthesized by a conventional solid-state reaction method and analysed by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and ultraviolet-visible spectroscopy techniques. The photovoltaic characteristics of the prepared samples have been studied by employing J-V measurements. The pattern of XRD depicted that the dominating phase in the sample with x = 0 is a rutile tetragonal phase with the P4 2 /mnm space group. An increase in GeO 2 concentration leads to an appearance and rise of another hexagonal phase structure of α-GeO 2 with the P3 2 21 space group. Data obtained from the UV-visible spectroscopy measurements reflect that the optical energy gap (E optical) increases with increasing GeO 2 content, while the optical refractive index decreases. J-V photovoltaic characteristics confirm that the DSSCs doped with low-concentration doping, x = 0.05 and 0.1 of GeO 2 have higher values for conversion efficiency (η), fill factor and short circuit current density (J sc) compared with samples with high-concentration doping (x = 0.2 and 0.3) of GeO 2. The present results showed that TiO 2-(GeO 2) x (x = 0.05 and 0.1 wt%) films are potential candidates for optical filter materials and optoelectrical and photo-conversion energy devices. Keywords. TiO 2 nanocrystallites; rutile-type TiO 2 ; optical energy gap; refractive index; efficiency.