Enhancing efficiency and stability of perovskite solar cells through two-step deposition method with the addition of cesium halides to PbI₂ precursor

Perovskite films with few defects play a key role in preparing high-performance perovskite solar cells (PSCs). Here, cesium halides, such as CsCl, CsBr, and CsI, were introduced as a modulator into 1st PbI₂ precursor for manipulating the crystallization of perovskite films. By introducing CsI dense homogeneous perovskite films with high crystallinity, preferential orientation, and a pure black perovskite phase were prepared. In addition, the carrier lifetime of perovskite films was significantly increased because of the suppressed nonradiative recombination. Correspondingly, the power conversion efficiency (PCE) of small-area devices using CsI regulation was increased from 17.45 to 20.29%. Furthermore, the device showed excellent stability maintaining 75% of its initial PCE after 350 h of continuous irradiation. This study demonstrates that CsI-added is a reliable way to prepare PSCs for practical applications.