RU(II) sensitized Nb2O5 solar cell made by the sol-gel process

Abstract

Since the development of dye sensitized nanocrystalline TiO2 solar cells by Grätzel et al., several other semiconducting electrode materials have been tested. The results obtained for solar cells of similar configuration using Nb2O5 layers are presented. 6µm thick Nb2O5 films have been deposited on conducting ITO or FTO glass by spin and dip coating process and sintered in air at 520°C. The layers are porous and crystalline with particle size ranging between 20 and 100 nm. Spectral sensitization of the films was carried out with a ruthenium(II)-complex, cis-Di(thiocyanato)-N,N'-bis(2,2'-bipyridyl-4,4'dicarboxylic acid)-ruthenium(II) dihydrate). The spectral incident photon to current conversion efficiency (IPCE) measured with a photoelectrochemical cell for a 4.9 cm2 electrode has a maximum value of 40% at 520 nm. Closed solar cells of different sizes have been built and their photocurrent, open circuit voltage, fill factor and efficiency have been measured under tungsten halogen lamp irradiation up to 1000 W/m2. The results obtained with a 0.2 cm2 closed cell for a 100 W/m2 (1/10 Sun) are isc=1.7 mA/cm2, Uoc=0.57 V, FF=0.55, η=5%. The conversion efficiency decreases with the light intensity. The influence of the Nb2O5 microstructure on the performance of the solar cell and a comparison with nanocrystalline TiO2 solar cell are presented.