Influence of co-electrodeposition parameters in the synthesis of kesterite thin films for photovoltaic

Abstract

Electrodeposition is one of the most attractive techniques for the synthesis of thin films chalcogenides for photovoltaic applications, in particular for earth abundant kesterite. In this work, the influence of core parameters of this technique, such as the applied potential and deposition time, on the chemical composition of co-deposited Cu–Zn–Sn precursors is studied. Indeed, how the precursor composition affects the final composition of Cu2ZnSnSe4 after reactive annealing in Se atmosphere is also investigated, not only at the film level but also in solar cell devices. X-ray based techniques (XRF and XRD) reveal that the chemical and phase composition of electrodeposited precursors is highly sensitive to small modifications (25 mV) of the applied potential during electrodeposition. Only when the applied potential is −1.2 V (vs. Ag/AgCl) the precursor composition matches to what is required for operating devices. Multi-wavelength Raman spectroscopy of selenized precursors confirms that lower potential than −1.2 V favor the formation of Sn-rich secondary and ternary compounds after selenization, while a higher overpotential led to the formation of ZnSe in the film. On the other hand, the use of longer deposition times enhance the incorporation of zinc in the film, modifies the morphology of the precursor and promotes the formation ZnSe after selenization. Photovoltaic devices were only obtained at an electrodeposition potential of −1.2 V, and reaching a maximum efficiency close to 5% for a 10 min electrodeposited CZT precursor.