RbF modified FTO electrode enable energy-level matching for efficient electron transport layer-free perovskite solar cells

Abstract The development of highly efficient electron transport layer free perovskite solar cells (ETL-free PSCs) with simplified and economical device configurations can significantly motivate the commercialization of PSCs. However, the performance of ETL-free PSCs has been hampered by the sluggish charge extraction and severe charge carrier recombination due to the energy-level mismatch at the interface of the perovskite and the transparent conductive electrode FTO (fluorine doped tin-oxide). In this study, this issue is well solved by modifying the FTO surface with a simple, low-cost and non-toxic rubidium fluoride (RbF) interlayer. An interfacial dipole layer is formed on the FTO surface by inserting a RbF layer, which tunes the work function of FTO, eliminates the electron transport barrier and optimizes the energy-level alignment at the FTO/perovskite interface, thereby enhancing the charge transfer and suppressing the carrier recombination. Consequently, the rigid ETL-free PSCs with RbF layer yield high efficiencies of up to 18.79%, higher than that of ETL-free devices on bare FTO (16.03%). By virtue of the low-temperature processability, a superior PCE of 15.7% has been achieved by flexible ETL-free PSCs fabricated on RbF modified plastic substrate. This study provides a simple, efficient and environmentally friendly approach to modify the FTO electrode for fabricating ETL-free PSCs, which contribute to promote the design of advanced interface materials for simplified and high-performance perovskite photovoltaics.