Effect of transparent substrate on properties of CuInSe2 thin films prepared by chemical spray pyrolysis

Abstract

In this paper, the properties of CuInSe₂ (CISe) films deposited on three transparent substrates (FTO, FTO/NiO_x, FTO/MoO₃) are studied. These substrates might be used for bifacial solar cells, in place of the conventional glass/Mo substrates. CISe layers are deposited by spray pyrolysis followed by a selenization process. For the same deposition conditions, the CISe layers on FTO show the largest grain size (~ 0.50 µm) and crystallinity, while FTO/MoO₃ substrates result in the smallest grains (~ 0.15 µm). The optical bandgap of the CISe films ranged from 1.35 eV for FTO substrate to 1.44 eV for FTO/MoO₃ substrate. All films show p-type conductivity, with the carrier densities of 1.6 × 10¹⁷ cm⁻³, 5.4 × 10¹⁷ cm⁻³, and 2.4 × 10¹⁹ cm⁻³ for FTO, FTO/NiO_x, and FTO/MoO₃ substrates, respectively. The CISe films also show different conduction, and valence levels, based on the substrate. In all cases, an ohmic behavior is observed between the CISe and substrate. The results demonstrate that CISe layer crystallinity, carrier concentration, mobility, and energy levels are strongly dependent on the chemical nature of the substrate. Bare FTO shows the most appropriate performance in terms of device requirements.