Unraveling Antisolvent Dripping Delay Effect on Stranski-Krastanov Growth of CH3NH3PbBr3 Thin Films: A Facile Route for Preparing Textured Morphology with Improved Optoelectronic Properties

Inorganic-organic hybrid perovskite materials have been a topic of interest for last few years due to their superior optoelectronic properties. However optical properties of perovskite materials are strongly dependent on the film morphology. Textured film morphology is expected to have higher light absorption as well as light out-coupling efficiency compared to smooth film. There have been numerous methods for controlling and optimizing film morphology to achieve high efficiency in solar cells and light emitting diodes. Here we have demonstrated that controlled anti-solvent treatment at low temperature can give Stranski-Krastanov growth in CH₃NH₃PbBr₃ thin films with superior optical and electronic properties for light emitting diode application. We have studied their photoluminescence properties at micro- to nano scale by fluorescence microscopy, hyper-spectral imaging and scanning near-field optical microscopy. We have demonstrated that the nanostructured micro-islands are highly emissive because of large quasi Fermi level splitting (QFLS) due to the localization of free charges in the smaller crystals. We have shown that the photoluminescence as well as electroluminescence can be improved by at least seven-fold due to the presence of micro-island on a smooth background film enhancing light out-coupling. Photo-induced photoluminescence enhancement is also observed in smooth film while micro-islands show photo-degradation.