Passivation of ultrathin nanoporous Tio2 for photovoltaic applications

Abstract

The passivation of sol-gel Ti02 by ultra-thin layers of AI-oxide has been investigated using transient and spectral photovoltage (SPV) techniques. The ultra-thin layers of AI-oxide were prepared by the ion-layer gas reaction (!LCAR) technique and modified by thermal treatments in air, vacuum or Ar/H2S atmosphere. Surface passivation of nanoporous Ti02 by ImS3 as well as charge transport in nanoporous - TiOz/lmS3/CuSCN composites is also investigated. The effect of annealing temperature and annealing periods were studied using their current-voltage characteristics and the results interpreted in terms of thermally instigated copper diffusion and effects of effective thickness of In2S3 in the nanocomposite. The increase of the diffusion length of a wet chemically prepared absorber ImS3 is demonstrated.

The samples were characterized by elastic recoil detection analysis (ERDAJ X-ray photoelectron spectroscopy (XPS), and contact potential difference (CPDJ transmission electron microscope (TEMJ scanning electron microscope (SEMJ energy dispersive X-ray (EDXJ and X-ray fluorescence (XRF) techniques. Without an AI-oxide surface layer, electronic states in the forbidden gap of Ti02 are formed during thermal treatments in vacuum and Ar/H2S. The trap density is strongly reduced at the Ti02/AI-oxide interface. A reduction of band gap states is seen in np- Ti02 with thin ImS3 surface layers. The formation of electronic defects is prevented by ultra-thin layer of AI-oxide or InzS3.