Combinatorial study of co-sputtered Cu2ZnSnS4 thin-film stoichiometry for photovoltaic devices

In this work we investigate the role of stoichiometry variations in Cu₂ZnSnS₄ thin films obtained via sulfurization of precursor grown by co-sputtering of binary sulphides. Combinatorially graded thin-film Cu-Zn-Sn-S library samples spanning a large region of the ternary Cu₂S-ZnS-SnS₂ phase diagram were deposited at temperatures below 110°C and subsequently sulfurized at 550°C in a tube furnace using a stoichiometric excess of sulfur. We present some results on the influence of chemical composition, measured by EDX, on the morphological and mechanical properties of the films. The films were also processed to obtain a matrix of small area complete photovoltaic devices. In this way the correlation between the stoichiometry and the device performances can be clarified. Finally, several interesting devices were more completely characterized by measuring J-V characteristic curves, the External Quantum Efficiency (EQE) and by looking at their photoluminescence (PL) spectrum trying to confirm a recently suggested correlation between PL peak energies and photovoltaic performances.