Formation of Intermediate-phase Free Ultrasmooth Quasi-two-dimensional Perovskite Films for High Quality Lasers

Ultrasmooth solution-processable quasi-2D perovskite thin films are of critical importance for many optoelectronic devices. In this work, we fabricated an ultrasmooth intermediate-phase free quasi-2D (PEA)2(FA)n-1PbnBr3n+1 perovskite film by using antisolvents with different polarities and boiling points to engineer the crystallization process. XRDs of perovskite powder showed that residual PbBr2 intermediate-phase could be eliminated using antisolvent DIE with low polarity and appropriate boiling point. The intermediate-phase free quasi-2D perovskite film has the narrowest FWHM, which indicates it exhibits better crystallinity. SEM and AFM images showed that intermediate-phase free film exhibits fewer pinholes and a more compact surface morphology. The intermediate-phase free quasi-2D perovskite displayed the smoothest surface with an RMS roughness of 1.82 nm, while that of the film with the residual intermediate-phase fabricated with antisolvent ethyl acetate (EA) is 4.83 nm. Time-resolved photoluminescence (TRPL) results show that the intermediate-phase free film has the longest charge carrier lifetime up to 1.24 ns, indicating it has the lowest trap density. Due to these improved qualities, the amplified spontaneous emission (ASE) threshold of the quasi-2D perovskite was reduced from 20.75 μJ cm-2 to 14.69 μJ cm-2. This work provides a method to fabricate ultrasmooth intermediate-phase free quasi-2D perovskite for high-performance optoelectronic devices.