Probing carrier trapping and hysteresis at perovskite grain boundaries via in situ characterization

Abstract

Plenty of trap states in the photo-active layer of perovskite solar cells (PSCs) have ineradicable impacts on device performance and long-term stability. Varied chemical agents have been applied as capping layer or precursor additives in order to enhance film quality and reduce trap state. However, there are still debates about whether these strategies exert the comparable effect on improvement of device performance and ambient stability. In addition, it is essential to clarify whether the agents would diffuse into the crystal lattice or aggregate at the grain boundaries to suppress ion migration. Herein, β-phenylethylammoniumiodide (β-PAI) was applied both as buffer layer and additive for perovskite materials and their underlying distinct roles in hysteresis reduction as well as trap deactivation were elucidated via in situ conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). For the fully open-air fabricated cells, β-PAI as additive can boost the maximum power conversion efficiency (PCE) of 20.24%, while as interlayer can maintain 96% of the initial PCE after 35 d under 35 ± 5%RH in ambient air. In the end, some mechanistic guidelines were proposed to clarify the distinct roles of additives and interlayer, which is beneficial for further chemical design in order to promote the performance and stability for perovskite devices.