Role of antisolvent-based two-step fabrication process in retention of structural stability of organic-inorganic perovskites

The organic-inorganic metal halide perovskites (OIMHPs) have been widely explored in recent years due to their competent performance in energy conversion and storage applications. We compare the time dynamics of structural, morphological, and optoelectronic attributes of Methylammonium lead Iodide (MAPbI3) thin films synthesized by a two-step solution processing route in two different ways, viz. without and with antisolvent vapor exposure. The time-dependent GIXD profiles reveal the better structural preservation of the antisolvent-exposed synthesized sample over 25 days, manifested by only slight emergence of PbI2 diffraction peak at 12.71°, unlike the other film devoid of antisolvent exposure where a strong PbI2 peak appears after 25 days, indicating the structural decomposition of MAPbI3. The structural degradation of the films devoid of antisolvent treatment is also corroborated by the appearance of an absorption onset at ~ 2.3 eV in the Tauc plot, attributed to the PbI2 bandgap. On the other hand, only a slight spectral shift, from ~ 1.55 eV (0 days) to ~ 1.67 eV (25 days), occurs in the assessed optical bandgap in the antisolvent-exposed films. A two-step mechanism, responsible for the structural phase retention in the antisolvent-exposed films, is proposed based on preferential intercalation and availability of more reaction sites that propel the exhaustive conversion of precursors leading to a structurally stable perovskite phase. This investigation may help address the issues of structural decomposition, which have been impeding the widespread application of OIMHPs into photovoltaics and other light energy harvesting applications.