Role of precursor solution in controlling the opto-electronic properties of spray pyrolysed Cu_2ZnSnS_4 thin films

摘要

Thin films of Cu_2ZnSnS4, a potential candidate for application as absorber layer in thin film solar cells, were successfully deposited on soda lime glass substrates using spray pyrolysis and the effect of variation of precursor on the structural and opto-electronic properties was investigated. We used stannous as well as stannic chloride as precursors of tin in the spray solution. All the films exhibited kesterite structure with preferential orientation along the (112) direction. But crystallinity and grain size were better for stannic chloride based films. Also they possessed a direct band gap of 1.5 eV and the absorption coefficient was >104 cm"1. Carrier concentration and mobility could be enhanced and the resistivity reduced by two orders by using stannic chloride in spray solution. Junction trials were performed with CZTS films prepared using stannic chloride precursor as the absorber layer and indium sulfide as the buffer layer. XPS depth profiling of the junction was done. Formation of CZTS could be confirmed and also information about the junction interface could be obtained from the XPS results. We obtained an open-circuit voltage of 380 mV and short-circuit current density of 2.4 mA/cm2.