The effect of metal-chelate complex in Cu2SnS3 thin film solar cells and their characteristics, photovoltaic performance, and defect analysis

Hybrid inks with a chelating agent were prepared and coated by a spin-coating method to form Cu2SnS3 (CTS) thin films. After the coating, a subsequent sulfurizing process via rapid thermal annealing was performed. During the sulfurization, the Cu and Sn precursors in the hybrid inks exist in complex forms with chelates and these complexes help to form the CTS thin films by controlling the reaction rate of the metal precursors. Additionally, even though the complexes with chelates were formed, the oxidation numbers of the metal precursors were affected by the ionization tendency of each metal in the hybrid inks to form the semiconducting CTS thin films. After obtaining the optimum sulfurizing condition by controlling the reaction pressure and temperature, the CTS thin films were characterized and CTS solar cells were fabricated under these conditions. The best conversion efficiency of the fabricated cells was 2.953% and the temperature-dependent photovoltaic performances were also examined to investigate the carrier transport mechanisms of the devices. According to admittance spectroscopy, the dominant defect energy level was determined as 0.09 eV above the valence band minimum, which accords with the copper vacancy (V-Cu) level. In addition, capacitance-voltage measurements and drive-level capacitance profiling were applied to demonstrate the carrier densities and defect behaviors.