WS₂: A New Window Layer Material for Solar Cell Application

Radio frequency (RF) magnetron sputtering was used to deposit tungsten disulfide (WS₂) thin films on top of soda lime glass substrates. The deposition power of RF magnetron sputtering varied at 50, 100, 150, 200, and 250 W to investigate the impact on film characteristics and determine the optimized conditions for suitable application in thin-film solar cells. Morphological, structural, and opto-electronic properties of as-grown films were investigated and analyzed for different deposition powers. All the WS₂ films exhibited granular morphology and consisted of a rhombohedral phase with a strong preferential orientation toward the (101) crystal plane. Polycrystalline ultra-thin WS₂ films with bandgap of 2.2 eV, carrier concentration of 1.01 × 10¹⁹ cm^-3, and resistivity of 0.135 Ω-cm were successfully achieved at RF deposition power of 200 W. The optimized WS₂ thin film was successfully incorporated as a window layer for the first time in CdTe/WS₂ solar cell. Initial investigations revealed that the newly incorporated WS₂ window layer in CdTe solar cell demonstrated photovoltaic conversion efficiency of 1.2% with V_oc of 379 mV, J_sc of 11.5 mA/cm², and FF of 27.1%. This study paves the way for WS₂ thin film as a potential window layer to be used in thin-film solar cells.