Investigation of Cu₂ZnSnS₄thin films with controllable Cu composition and its influence on photovoltaic properties for solar cells

The effects of Cu composition on the structural, morphological, optical properties of Cu₂ZnSnS₄(CZTS) films prepared by RF magnetron sputtering and a post sulfurization, and CZTS solar cells performance have been investigated. The crystal structure characterized by XRD patterns, Raman and far-infrared spectra reveal that the secondary phases (e.g. SnS and Cu₂SnS₃) can be suppressed effectively by manipulating the Cu content in CZTS thin films. Furthermore, morphological studies indicate that the CZTS thin film with low Cu content shows a bilayer structure, while that with high Cu content exhibits the grain growth throughout the entire absorber film with some voids at the Mo/CZTS interface. Finally, a Cu-poor CZTS solar cell with 3.46% is fabricated. Temperature and excitation-power dependent Photoluminescence measurement reveals the radiative recombination between electrons in conduction band tails and holes bound to the neighboring acceptors levels in Cu-poor CZTS device. The diode parameters of Cu-poor CZTS solar cell are extracted and used to discuss the possible reason for limiting efficiency.