Structural evolution of chemically deposited binary stacks of Sb2S3-CuS to phase-pure CuSbS2 thin films and evaluation of device parameters of CuSbS2/CdS heterojunction

Copper-based chalcogenide ternary compounds are promising materials to be used as absorber layer in solar cells. In this work, we have reported the preparation of copper antimony sulfide (CAS) thin films by annealing chemically deposited multi-stack of Sb2S3-CuS and the effect of thickness ratio between two binary sulfides on the formation of different crystalline phases of Cu-Sb-S system. A series of multilayer structure was prepared with different thickness of CuS in order to study the effect of copper concentration on the structural, morphological, optical, and electrical properties of the resulting CuxSb1-xSy films. The CAS films were characterized by several techniques such as X-ray diffraction, Raman scattering, UV-visible spectroscopy, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Hall effect measurements to evaluate their physical properties. The formation of either pure chalcostibite (CuSbS2) or mixed ternary phases containing chalcostibite, famatinite (Cu3SbS4), and tetrahedrite (Cu12Sb4S13) were detected depending on the thickness ratio of Sb2S3 and CuS. Chalcostibite films revealed desired optical and electrical values. Finally, solar cell was fabricated using the heterostructure FTO/CdS/ CuSbS2/Ag and characterized by current-voltage, capacitance-voltage, and impedance-spectroscopy measurements achieving a promising similar to 0.8% efficiency with V-OC = 0.484 V, J(SC) = 5.97 mA/cm(2), and FF = 27.34%. Impedance measurements revealed a low series resistance in the optimal solar cell, as a result, an increment in open circuit voltage. Novelty Statement The novelty of this work is the fabrication of CuSbS2 thin films by tuning the thickness ratio of binary sulfides in Sb2S3-CuS stack followed by proper thermal annealing. Furthermore, impedance spectroscopic studies of CuSbS2 solar cell are still lacking; the present study may provide important physical insight to understand the device performance and possibilities toward any further improvement.