Role of carbon quantum dot for enhanced performance of photo-absorption in Cu2CoSnS4 superstrate solar cell device

Abstract

In the present work, superstrate type ITO/CdS/Cu₂CoSnS₄ (CCTS) and Cu₂CoSnS₄:CQD (CCTS:CQDs)/Al thin-film solar cells are reported. An attempt was made to fabricate CCTS and CCTS:CQD thin-film absorbers using spray pyrolysis at a deposition temperature of 170 °C. In order to increase the crystallization performance, thin films were annealed at 250 °C for 30 min under N₂ atmosphere using rapid thermal annealing. The XRD results showed the formation of the stannite structure for both CCTS and CCTS:CQD and the phase purity was confirmed by Raman analysis. The XPS spectra indicated oxidation states of Cu, Co, Sn, and S to be Cu⁺, Co²⁺, Sn⁴⁺, and S²⁻ in CCTS and CCTS:CQD films. The band gap of the films was obtained as 1.35 and 1.26 eV for CCTS and CCTS:CQD. The CCTS:CQD device shows an improved efficiency (0.07%) over the CCTS device (0.003%). Impedance measurement was performed to analyze the interface between contacts and the bulk. These results showed that carbon quantum-dot-based chalcogenides can effectively absorb UV-visible photons and separate electrons and holes as potential candidates for future low-cost large-area inorganic solar cells.