The crystallisation of Cu2ZnSnS4 thin film solar cell absorbers from co electroplated Cu Zn Sn precursors

The best CZTS solar cell so far was produced by co sputtering continued with vapour phase sulphurization method. Efficiencies of up to 5.74 were reached by Katagiri et al. The one step electrochemical deposition of copper, zinc, tin and subsequent sulfurization is an alternative fabrication technique for the production of Cu2ZnSnS4 based thin film solar cells. A kesterite based solar cell size 0.5 cm2 with a conversion efficiency of 3.4 AM1.5 was produced by vapour phase sulfurization of co electroplated Cu Zn Sn films. We report on results of in situ X ray diffraction XRD experiments during crystallisation of kesterite thin films from electrochemically co deposited metal films. The kesterite crystallisation is completed by the solid state reaction of Cu2SnS3 and ZnS. The measurements show two different reaction paths depending on the metal ratios in the as deposited films. In copper rich metal films Cu3Sn and CuZn were found after electrodeposition. In copper poor or near stoichiometric precursors additional Cu6Sn5 and Sn phases were detected. The formation mechanism of Cu2SnS3 involves the binary sulphides Cu2 xS and SnS2 in the absence of the binary precursor phase Cu6Sn5. The presence of Cu6Sn5 leads to a preferred formation of Cu2SnS3 via the reaction educts Cu2 xS in the presence of a SnS2 Cu melt. The melt phase may be advantageous in crystallising the kesterite, leading to enhanced grain growth in the presence of a liquid phas