Optimization of NiOₓ thin film properties and its impact on the performance of bifacial Sb₂Se₃ solar cells

Abstract

NiOₓ thin films show promise in Sb₂Se₃ thin film solar cells, though the optimal oxygen stoichiometry (x) remains undetermined. While most solar cells use single-sided illumination. This study demonstrates a high-performance bifacial Sb₂Se₃ solar cell with a superstrate configuration (FTO/NiOₓ/Sb₂Se₃/CdS/i-ZnO/ITO/Al), utilizing NiOₓ hole transport layer (HTL) deposited via reactive sputtering. The device's performance under single and bifacial illumination conditions was systematically investigated, along with oxygen/argon flow ratio (OAFR) optimization. At OAFR = 10 %, NiOₓ exhibited optimal stoichiometry (x = 1.04), complete columnar crystallization, and balanced Ni³⁺/Ni²⁺ ratio, resulting in high visible transmittance (81 %) and a bandgap of 3.78 eV. Under FTO-side single illumination, the device achieved an open-circuit voltage (Voc) of 0.36 V, short-circuit current density (Jsc) of 23.16 mA/cm², fill factor (FF) of 54.46 %, and power conversion efficiency (PCE) of 4.86 %. The bifacial configuration demonstrated enhanced performance primarily through additional light harvesting from both front and rear illumination. The optimized NiOₓ HTL further supported this enhancement through efficient hole extraction and reduced interface recombination. These synergistic effects improved device performance with Jsc increasing to 29.93 mA/cm², Voc reaching 0.414 V, and achieving a PCE of 6.72 %. The device achieves a bifaciality factor of 0.90, showing balanced performance. With an albedo factor of 0.2, the bifacial efficiency gain reaches 18 %.