Solvent-dependent self-assembly of two dimensional layered perovskite (C6H5CH2CH2NH3)2MCl4 (M = Cu, Mn) thin films in ambient humidity

Abstract

Two dimensional layered organic-inorganic halide perovskites offer a wide variety of novel functionality such as solar cell and optoelectronics and magnetism. Self-assembly of these materials using solution process (ex. spin coating) makes crystalline thin films synthesized at ambient environment. However, flexibility of organic layer also poses a structure stability issue in perovskite thin films against environment factors (ex. moisture). In this study, we investigate the effect of solvents and moisture on structure and property in the (C₆H₅(CH₂)₂NH₃)₂(Cu, Mn)Cl₄ (Cu-PEA, Mn-PEA) perovskite thin films spin-coated on Si wafer using three solvents (H₂O, MeOH, MeOH + H₂O). A combination of x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) show that relative humidity (RH) has a profound effect on perovskite thin films during sample synthesis and storage, depending on the kind of solvent used. The ones prepared using water (Cu-PEA:H₂O, Mn-PEA:H₂O) show quite different behavior from the other cases. According to time-dependent XRD, reversible crystalline-amorphous transition takes place depending on RH in the former cases, whereas the latter cases relatively remain stable. It also turns out from XAS that Mn-PEA thin films prepared with solvents such as MeOH and MeOH + H₂O are disordered to the depth of about 4 nm from surface.