Highly phase-pure spray-pyrolysed Cu2SnS3 thin films prepared by hybrid thermal treatment for photovoltaic applications

The structure and physical properties of thin films of ternary photovoltaic absorber Cu2SnS3 on soda-lime glass substrate deposited by cost effective spray pyrolysis following a hybrid thermal annealing (HTA) have been investigated. The advantage of HTA-sulfurization over standard thermal annealing (STA) and rapid thermal annealing (RTA) is established for Cu2SnS3 (CTS). The X-Ray diffraction (XRD) and Raman spectroscopy reveals highly phase pure Cu2SnS3 is produced through effective relaxation of compressive stress and increased crystallinity by the HTA-sulfurization step. Additionally, scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDX) reveals that the evolution of secondary phases, CuxSy (x, y: 116, 64; 2, 1; 1.8, 1; 51, 27; 6, 6 etc) could be effectively prevented by the HTA process over the STA and RTA. The optimized HTA-CTS thin films obtained are of p-type conductivity with the carrier concentration, resistivity and mobility of 5.5 × 1020 cm−3, 9.8 × 10−3Ω-cm and 1.15 cm2V−1s−1, respectively. The optical band gap of about 1.65 eV with large absorption coefficient of 105 cm−1 demonstrates it as an ideal candidate for thin film solar cells. A solar cell configuration of glass/F:SnO2/CTS/CdS/ZnO:Al/Al shows an open circuit voltage of 225 mV.