Optimization of Sb ₂ Se ₃ thin-film solar cells: the role of absorber selenization and the CdS buffer layer

Abstract Sb 2 Se 3 has garnered significant interest as a potential material for photovoltaic (PV) devices, owing to its unique properties. Here, Sb 2 Se 3 thin films are grown by selenization of evaporated Sb layers. The Se content and maximum temperature during the selenization process control the composition of the semiconductor. In all cases, the Sb 2 Se 3 is orientated in the [hk1] direction. The increase of Se temperature results in larger grain size; however, the process temperature must be limited to 340 ° C to avoid a significant excess of Se and the formation of holes on the Sb 2 Se 3 surface, which leads to decreased performance of the ITO/ZnO/CdS/Sb 2 Se 3 /Mo/SLG device. As determined by surface photovoltage, combined Kelvin probe and photoelectron yield spectroscopy measurements, Sb 2 Se 3 thin films exhibit p-type conductivity with a doping concentration of approximately 4 × 10 15 cm −3 . Two different buffer layers, CdS1 and CdS2, are studied to form the heterojunction. The use of Na citrate as chemical reagent, along with modified chemical bath conditions for CdS2 deposition, results in enhanced PV performance, increasing the device efficiency from 3.6% to 5.4%. This improvement may be related to the superior optical properties of the CdS2 with higher bandgap energy and lower total reflectance, allowing for a higher carrier collection. The observed Cd diffusion towards the active layer, likely results in the formation of Cd i donors that contribute to a stronger downward band bending at the buffer/absorber interface, reducing interface recombination and enhancing open circuit voltage of the devices. Although the modification of the CdS layer plays a key role in improving the device performance, the efficiency of fabricated devices remains limited by interface recombination. A total area efficiency of 5.5% is achieved by reducing the thickness of Sb 2 Se 3 to 450 nm. This study demonstrates the relevance of optimizing the CdS/Sb 2 Se 3 heterointerface to produce efficient Sb 2 Se 3 PV devices.