Development of cost-effective solution-processed Cu2ZnSn(SxSe1-x)4 thin-film photovoltaic devices

This study focused on preparing Cu2ZnSn(SxSe1-x)4 (CZTSSe) kesterite thin films by selenizing a non-toxic Cu2ZnSnS4 (CZTS) precursor ink, exploring the effects of sodium incorporation and varied annealing temperatures on their suitability for photovoltaic applications. Analysis confirmed the formation of a pure kesterite phase but revealed adverse defects like ZnCu and ZnSn due to copper enrichment on the absorber surface region and zinc enrichment on the absorber bulk region, respectively, affecting photovoltaic performance. Interfacial Mo(S, Se)2 was observed near the absorber-Mo layer interface, with its thickness increasing proportionally with the annealing temperature. The energy bandgap of CTZSSe thin films varied 0.91–0.96 eV, with Urbach energy increasing as the band tail expanded into the forbidden gap. Regarding photovoltaic performance, solar cells fabricated without a sodium layer demonstrated an efficiency of 0.8%, with Voc = 277 mV, Jsc = 8.93 mA/cm2, and FF = 32.19%. Conversely, solar cells with sodium layers, namely SSe1_Na and SSe2_Na, exhibited maximum efficiency of 1.4% (Voc = 259 mV, Jsc = 20.42 mA/cm2, and FF = 26.5%). Cross-sectional imaging unveiled voids or small cracks between the absorber and back contact layers in the SSe1_Na and SSe1 thin film solar cells, potentially causing cell shunting and diminishing device performance. Defect studies on CZTSSe thin films highlighted an increase in detrimental defect states (e.g. ZnCu and ZnSn), which could lead to quasi-acceptor-donor pair recombination during the recombination process. [Display omitted] •The CZTSSe absorbers layers were fabricated by selenizing the spin-coated CZTS precursors W & W/O Na.•The impact of sodium and temperatures on the material and PV properties have been investigated.•Encouragements of the method are short fabrication time and no possibly harmful materials are used.•The photovoltaic performance of the CZTSSe and CZTSSe:Na Photovoltaic devices were discussed.