Defect control based on interfacial passivation via post-treatment of 1-ethylpyridine hydrobromide for achieving efficient and stable perovskite solar cells

The carrier recombination caused by a series of crystal defects in perovskite materials is still the main obstacle to further improve the photoelectric conversion efficiency. Herein, as an agent for interfacial engineering, 1-ethyl -pyridine hydrobromide (EPB) was employed to treat the FA1-xMAxPbI3-yBry perovskite film using a two-step sequential deposition method. The influence and mechanism of the post-treatment with EPB on the film prop-erties and photovoltaic performance of the relevant perovskite solar cells (PSCs) were studied. The champion EPB-treated perovskite solar cell achieved a remarkable power conversion efficiency (PCE) of 20.71 % with an enhanced short current density (Jsc) of 24.14 mA cm-2, which is higher than that (PCE = 18.85 %, Jsc = 23.40 mA cm-2) of the pristine device without EPB. The nitrogen (N) atom in EPB exhibits a strong coordination with lead (Pb) from the perovskite, which reduces defect density and suppresses non-radiative recombination for achieving high-performance PSCs. The UV-vis and UPS results reveal that the effective passivation effect of EPB reduces the drop of the valence band between perovskite and SpiroOMeTAD, which effectively promoting the interfacial transport of carriers. As a result, The PCE of the EPB-treated device remains more than 90 % of the initial efficiency after 400 h of unpackaged and about 40 % ambient humidity.