Large grain growth in Cu2ZnSnS4 thin films in the absence of Na using rapid thermal annealing

Abstract

Larger grain sizes and crystallographic texture in the absorber layer are correlated with performance in polycrystalline inorganic thin film solar cells because they lead to reduced densities of recombination centers and traps at grain boundaries. In this work, we compare the effects of rapid thermal annealing (RTA) and furnace annealing on film morphology, grain growth, and crystallographic texture in Cu2ZnSnS4 (CZTS) thin films deposited on Mo-coated glass by RF cosputtering. Using x-ray diffraction (XRD),scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), we show that RTA induces significant grain growth and texture without the degradation of the substrate caused in furnace annealing by the high temperatures required for CZTS phase formation. CZTS grains grown in RTA annealed samples were 2–3 times larger than those in furnace-annealed samples. Significantly, this is demonstrated in RTA on sodium-free glass which implies that RTA and similar processing methods may be capable of producing desirable CZTS grain distributions on alternative substrates such as metal foil, plastic, or thin glass.