Use of delafossite oxides CuCr1-xGaxO2 nanocrystals in p-type dye-sensitized solar cell

Abstract

Pure phase of CuCr1-xGaxO2 (x = 0.10, 0.20, 0.30, 0.40, 0.50.) nanocrystals with the crystal size ranging from 15 nm to 50 nm were synthesized through hydrothermal method. The crystal structure, morphology, element composition information, optical properties and valence band energy position of these delafossites were analyzed by XRD, SEM/EDS, TEM/EDS, XPS/UPS, and Uv–vis measurements. It was found that the Ga3+ ions were perfectly substituted at Cr3+ in CuCrO2 lattice and finally formed the CuCr1-xGaxO2 solid solution. The crystal size of CuCr1-xGaxO2 enlarged from 15 nm to 50 nm with the increasing of Ga composition x from 0.10 to 0.50. The optical transmittance of these CuCr1-xGaxO2 films approached about 60–75% in the visible region and the direct band gap values around 3.25–3.30 eV. The valence band energy position of these CuCr1-xGaxO2 nanocrystals ranged from 5.29 to 5.44 eV, which is much lower than traditional NiO nanoparticles used in p-type dye sensitized solar cells (DSSCs). Moreover, these CuCr1-xGaxO2 nanocrystals were applied as photocathodes in p-type DSSC devices, and the CuCr0.90Ga0.10O2 based solar cell show the best performance (134 mV, 1.56 mA cm−2, 0.10%) after roughly optimizing the composition and the thickness of photocathode films.