Impurity Phases and Optoelectronic Properties of CuSbSe2 Thin Films Prepared by Cosputtering Process for Absorber Layer in Solar Cells

Sara Kim,Nam-Hoon Kim

doi:10.3390/coatings10121209

Abstract

When there is a choice of materials for an application, particular emphasis should be given to the development of those that are low-cost, nontoxic, and Earth-abundant. Chalcostibite CuSbSe2 has gained attention as a potential absorber material for thin-film solar cells, since it exhibits a high absorption coefficient. In this study, CuSbSe2 thin films were deposited by radio frequency magnetron cosputtering with CuSe2 and Sb targets. A series of CuSbxSe2 thin films were prepared with different Sb contents adjusted by sputtering power, followed by rapid thermal annealing. Impurity phases and surface morphology of Cu–Sb–Se systems were directly affected by the Sb sputtering power, with the formation of volatile components. The crystallinity of the CuSbSe2 thin films was also enhanced in the near-stoichiometric system at an Sb sputtering power of 15 W, and considerable degradation in crystallinity occurred with a slight increase over 19 W. Resistivity, carrier mobility, and carrier concentration of the near-stoichiometric thin film were 14.4 Ω-cm, 3.27 cm2/V∙s, and 1.33 × 1017 cm−3, respectively. The optical band gap and absorption coefficient under the same conditions were 1.7 eV and 1.75 × 105 cm−1, which are acceptable for highly efficient thin-film solar cells.

Highlights

Considerable attention has recently been given to thin-film solar cells based on high-efficiency absorbers owing to their applicability in flexible photovoltaic technology
The surface morphology of Cu–Sb–Se thin films deposited at different Sb powers was analyzed using field emission scanning electron microscope (FESEM)
A gap on the surface appeared in the annealed thin films at 15 W which was not seen in the as-deposited thin films under the same sputtering power

Summary

Introduction

Considerable attention has recently been given to thin-film solar cells based on high-efficiency absorbers owing to their applicability in flexible photovoltaic technology. The window in Cu:Sb:Se ratio for creating CuSbSe2 seems to be narrow and needs to be close to 1:1:2 to prevent the formation of these secondary phases Some of these phases are highly conductive and can cause a shunting effect [18], while some of these phases such as Sb2 Se3 have excellent optoelectronic properties [11], so strict phase control is important for the prevention of these destructive effects. The importance of rigorous control of the Cu content in thin films for the prevention of phases such as Cu2 Se and Cu3 SbSe3 has been emphasized in many previous reports [5,6,12], when the Sb content is another important factor for the prevention of these secondary phases Several methods, such as electrodeposition, pulsed laser deposition, sequential evaporation with selenization, spin-coating, and pre-sputtering of Cu with close-spaced sublimation of Sb2 Se3 , have been reported to prepare CuSbSe2 thin films [19]. Phase and crystal orientation evolution with changing Sb content were investigated for the absorber materials in thin-film solar cells

Experimental Details

Results and Discussion

Conclusions