Enhancing perovskite solar cell efficiency: ZnO-WO as an electron transport layer to minimize recombination losses.

Tungsten trioxide (WO), with strong electron affinity and recombination suppression, serves as an effective electron transport layer (ETL). Incorporating zinc oxide (ZnO) enhances its conductivity, forming a ZnO-WO composite with improved charge extraction and energy level alignment. The novelty of this study is to introduce ZnO-WO as an interlayer ETL in CsPbIBr-based perovskite solar cells, enabling superior device performance and stability. Both WO and ZnO-WO films were synthesized sol-gel spin coating. X-ray diffraction (XRD) confirmed the monoclinic phase for both films, with ZnO-WO exhibiting a larger crystallite size (67.7 nm) and lower dislocation density (2.18 × 10 lines per m). Raman spectroscopy revealed additional ZnO vibrational modes, indicating lattice reinforcement and enhanced structural integrity. Scanning electron microscopy (SEM) shows that ZnO-WO films have larger, more uniform grains and smoother morphology than WO, indicating improved film quality. UV-vis analysis showed a redshift and reduced bandgap (2.74 eV), while PL spectra indicated lower defect-related recombination. Time-resolved photoluminescence (TRPL) shows reduced average decay time for ZnO-WO, indicating faster carrier dynamics. Devices with ZnO-WO achieved a power conversion efficiency of 12.87% due to reduced charge transfer resistance (21 Ω) and higher recombination resistance (4605 Ω), as confirmed by electrochemical Impedance Spectroscopy (EIS). External Quantum Efficiency (EQE) of 95% further demonstrated enhanced charge collection, establishing ZnO-WO as a promising ETL for high-efficiency PSCs.