Promoting the grain growth of CZTSSe solar cells by incorporating Sb2Se3 and annealing in an atmosphere devoid of toxic selenium

Abstract

The large amounts of grain boundaries caused by small grains in Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber tend to form recombination centers for photogenerated electron–hole pairs, thereby limiting the performance improvement of solar cells. In this work, CZTS precursor films were fabricated through spin-coating of the precursor solution, followed by annealing in a selenium-free argon atmosphere. To promote grain growth in the absorber, Sb₂Se₃ layers were strategically incorporated at different positions of the precursor films. Absorbers with double Sb₂Se₃ layers and without Sb₂Se₃ layers were prepared for comparison. After incorporating double Sb₂Se₃ layers, the grain size of the absorbers increased from about 50 nm to over 1 μm, while the transport barrier and recombination of electron–hole pairs were reduced. As a result, the efficiencies of solar cells improved from 4.36% to 6.24%. To evaluate the action of Sb₂Se₃, the properties of Sb₂Se₃ were also investigated, and their impact on CZTSSe grain growth was elucidated. During annealing, Sb₂Se₃ decomposed, producing Sb and Se vapors. These species supplied energy for grain growth through mass transport along the grain boundaries, and Se could also partially substitute for S to achieve CZTSSe absorber. The incorporation of Sb₂Se₃ provides a promising approach to enhancing grain growth and improving the performance of CZTSSe solar cells while avoiding the use of a toxic selenium atmosphere.