Influence of deposition technique on the structural and optical properties of CuS thin films for hole transport layers

This study presents a direct comparison of copper (II) sulfide (CuS) thin films fabricated by spin coating and doctor blade coating as hole transport layers (HTLs) in perovskite solar cells (PSCs). Both sets of films were fully characterized using Xray diffraction (XRD) to determine crystallinity and grain size, scanning electron microscopy (SEM) for morphology, energydispersive Xray spectroscopy (EDAX) for composition, ultraviolet-visible (UV-Vis) spectroscopy for optical bandgap, Xray photoelectron spectroscopy (XPS) for surface chemistry, and ultraviolet photoelectron spectroscopy (UPS) for energy-level alignment and found to be crystalline and phase-pure. Doctor bladecoated films exhibited larger crystallite sizes (≈ 44.9 nm vs. 37.45 nm), slightly lower band gaps (3.15 eV vs. 3.23 eV), and despite higher microstrain and dislocation density, a closer valence band maximum (VBM = - 5.44 eV vs. - 5.99 eV) and conduction band minimum (CBM = - 2.29 eV vs. - 2.76 eV) to the MAPbBr₃ perovskite absorber. When these experimental parameters were incorporated into three-dimensional drift-diffusion simulations under AM1.5G illumination, the doctor blade HTL yielded a projected power conversion efficiency of 41.7% driven by high charge density (> 10²⁴ cm⁻³) and low recombination rates (~ 1 × 10⁻⁵ s⁻¹) compared to 39.5% for the spincoated film. These results demonstrate that, while both deposition methods produce viable CuS HTLs, the doctor blade technique offers superior energylevel compatibility, scalable processing, and costeffectiveness for highefficiency, largearea PSC manufacturing.