Metal oxide electron transport bilayers to improve electron transport in planar perovskite solar cells

Abstract

In this work, we investigate the use of metal oxide bilayer ETLs, including ZnO/SnO₂, ZnO/WO₃, and SnO₂/WO₃, to enhance charge transport and suppress recombination in planar PSCs. The proposed bilayer architecture introduces improved interfacial contact, reduced defect density, and favorable energy level alignment compared to single-layer ETLs. Perovskite films grown on these bilayers were carefully examined with XRD, FTIR, SEM, UV-visible spectroscopy, photoluminescence, and impedance analysis. The films showed a stable tetragonal rutile crystal structure and similar light absorption edges around 752 nm, while photoluminescence quenching (up to 72.8% for ZnO/WO₃) indicated more efficient charge extraction. Electrical measurements confirmed improved ohmic contact and reduced resistivity, with ZnO/WO₃ showing the best performance. Among the studied devices, the ITO/ZnO/WO₃/MAPbI₃/MoO₃/Al configuration exhibited the best performance, achieving a power conversion efficiency (PCE) of 2.80%, with an open-circuit voltage (V_OC) of 481.9 mV, a short-circuit current density (J_SC) of 14.9 mA/cm², and a fill factor (FF) of 0.39. In contrast, devices based on single-layer ETLs showed significantly lower efficiencies, with ZnO and WO₃ yielding PCEs of 1.39% and 1.23%, respectively.  Overall, the bilayer ETLs facilitated smoother charge transfer, minimized recombination losses, and enhanced interfacial quality, demonstrating a simple yet effective approach to boost the efficiency of perovskite solar cells compared to conventional single-layer ETLs.

KEY WORDS: Solar cells, Perovskite, Electron transport bilayer, Charge dynamics

Bull. Chem. Soc. Ethiop. 2026, 40(11), 2415-2432                                                        

DOI: https://dx.doi.org/10.4314/bcse.v40i11.10