Enhancing perovskite solar cell efficiency: ZnO–WO3 as an electron transport layer to minimize recombination losses

Abstract

Tungsten trioxide (WO₃), 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–WO₃ composite with improved charge extraction and energy level alignment. The novelty of this study is to introduce ZnO–WO₃ as an interlayer ETL in CsPbIBr₂-based perovskite solar cells, enabling superior device performance and stability. Both WO₃ and ZnO–WO₃ films were synthesized via sol–gel spin coating. X-ray diffraction (XRD) confirmed the monoclinic phase for both films, with ZnO–WO₃ exhibiting a larger crystallite size (67.7 nm) and lower dislocation density (2.18 × 10¹⁴ lines per m). Raman spectroscopy revealed additional ZnO vibrational modes, indicating lattice reinforcement and enhanced structural integrity. Scanning electron microscopy (SEM) shows that ZnO–WO₃ films have larger, more uniform grains and smoother morphology than WO₃, 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–WO₃, indicating faster carrier dynamics. Devices with ZnO–WO₃ 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–WO₃ as a promising ETL for high-efficiency PSCs.