Buried interface modulation by rubidium dihydrogen phosphate towards highly effective perovskite solar cells

In perovskite solar cells (PSCs), the interface defects between the perovskite active layer (PVK) and the electron transport layer (ETL) represent a primary constraint impacting both efficiency and stability. To modulate the buried interface, a multifunctional molecule of rubidium dihydrogen phosphate (RbDP) was inserted into the buried interface. To see clearly the situation and structure of the perovskite bottom layer and deeply understand the influence of the buried interface, the ETL/PVK is peeled off. Various electrochemical characterizations indicate that the modulation of RbDP effectively diminishes amorphous regions and defects, alleviates in-plane tensile strain, reduces defects at the buried interface and inside of perovskite, and facilitates the extraction and transportation of charge carriers. Thus, the power conversion efficiency (PCE) of RbDP-modified formamidinium-based PSCs was 24.52 %, over the pristine device's 22.04 %. Furthermore, the unencapsulated RbDP-based device retains an initial efficiency of 90 % after 150 days of follow-up testing in the humidity range of 40 ± 10 %.