Influence of the precursor composition on the resulting absorber properties and defect concentration in Cu2ZnSnSe4 absorbers

Abstract

In this paper the influence of composition variations during the growth of Cu2ZnSnSe4 (CZTSe) layers on defect concentrations and final absorber properties is analyzed. The samples are prepared from sputtered metallic and alloyed Zn/Cu–Sn/(Sn)/Zn precursors. The variation of sputtered Sn content facilitates different forms for the embedded Sn (Cu3Sn, Cu6Sn5, elemental Sn). The predominating formation reaction during the subsequent annealing is tuned by the ratio of the alloys and the overall chemical composition in the precursor. During the high temperature stage of CZTSe formation the layer undergoes an in-process composition shift (Sn content variation), after which the final absorber composition is reached. As all absorbers are reaching a comparable end composition, in this paper the influence of the different precursor compositions and corresponding reaction pathways on the resulting defects and optoelectronic properties of the absorbers are addressed. Spectroscopic investigations were used to extract the defect configuration of the absorbers. The results are complemented with device performance measurements. Preferable precursor compositions leading to lower defect concentration and improved photoluminescence quantum-yield is identified. The obtained Urbach energy and VOC deficit are among the most promising results measured in our laboratories.