One-step electrodeposited CuInSe2 absorber layers for efficient PV cells

Thin polycrystalline CuInSe2 (CIS) films for photovoltaic (PV) applications were deposited on molybdenum (Mo)-coated soda lime glass substrates by the one-step electrodeposition process. Films growth was carried out using low concentration aqueous sulfate-based single baths containing dilute CuSO4.5H2O, In2(SO4)3.H2O and SeO2. The electrodeposited CIS layers were studied using SEM, EDS, X-ray diffraction and optical analyses. It was found that film microstructure, composition and morphology strongly depend on the initial concentrations of Cu(II), In(III) and Se(IV) electro-active ionic species in the electrochemical bath. Investigations on the films structure have shown that as-deposited samples are composed of microcrystalline and/or amorphous materials and require recrystallization at high temperature for device processing. Annealing in H2Se atmosphere at 450 °C led to highly crystallized thin films exhibiting the chalcopyrite structure with a pronounced (112) orientation. Optimized processing conditions for high quality thin CIS absorber materials have been established and subsequent photovoltaic (PV) devices exhibited ~ 9% efficiency