Fluorine-induced surface modification to obtain stable and low energy loss zinc oxide/perovskite interface for photovoltaic application

Despite its superior optoelectronic properties, the use of zinc oxide (ZnO) as an electron transport layer (ETL) is limited compared to that of TiO₂ and SnO₂ due to its chemical instability with perovskite. Although several approaches have been presented to alleviate this instability, the use of all-metal halides has not been reported. In this study, we develop stable ZnO/perovskite interfaces through a single-step post-annealing surface modification. The ZnO surface is modified using ammonium fluoride (NH₄F) solutions with different concentrations, thereby optimizing the ETL/perovskite interface to simultaneously reduce the loss and increase the stability while maintaining the photoconversion efficiency. Furthermore, the influence of the fluorine concentration on the physical, chemical, optical, and electrical properties of ZnO thin films is investigated. The photovoltaic performance of the planar perovskite solar cell fabricated using the surface-modified ZnO, as the ETL is nearly three times higher than that of the cell obtained using the control. The proposed technique can serve as a facile and holistic approach to enhance the chemical stability and device performance in photovoltaic and optoelectronic applications, irrespective of the ETL and perovskite materials. Graphical abstract: Fluorine-induced surface modification passivates surface defects on the ZnO surface, which improves the photovoltaic performance and ZnO/perovskite interface stability [Figure not available: see fulltext.]