Aprotic Solvent Effect in Preparation of Organo Lead Iodide Perovskite Nanowires by Two-Step Spin-Coating Procedure

Abstract

Lead-iodide perovskite (CH3NH3PbI3 ≡ MAPbI3) nanowires (NWs) were prepared by a two-step spin-coating technique by modifying one of the perovskite precursors with a small amount of aprotic solvent. In the two-step spin-coating technique, the perovskite precursors are MAI and PbI2. The first MAI powder is dissolved in isopropanol (IPA) to produce an isopropanol-MAI solution, while the second PbI2 is used in N, N-dimethylformamide (DMF) as an aprotic solvent. Here, a small amount of DMF was used with an IPA solution of MAI to grow 1D NWs based on MAPbI3 perovskite. Then, the film was formed directly from the MAPbI3 perovskite nanowires (PNWs) by coating the PbI2 layer with an IPA solution of MAI modified by DMF. The amount of DMF in the MAI/IPA solution was adjusted in the range between 0 and 50 μl. One-dimensional (1D) PNWs (∼100 nm diameter) and three-dimensional (3D) perovskite nanocrystals are compared. The structural and optical properties of the PNWs films are systematically investigated using X-ray diffraction patterns (XRD), scanning electron microscopy images (SEM), UV–vis absorption, and photoluminescence (PL). The result is that the presence of an additional solvent and its optimized amount in the MAI/IPA solution can increase the length and efficiency of charge transfer by facilitating perovskite transformation, as evidenced by the intensity of PL and the formation of a high-quality perovskite film. Compact, hole-free films with low trap states (crystal defects) were obtained. Further investigation of the lead iodide perovskite showed that reducing the dimensionality from 3D to 1D resulted in shorter wavelengths of the absorption edge and the PL peak in both the absorption and PL spectra. The shorter wavelengths indicate more localized exciton states in NWs. Finally, the amplified spontaneous emission (ASE) properties were obtained under picosecond laser excitation and a low ASE threshold was found at 10 and 53 μJ/cm2 for 1D and 3D, respectively, at about 300 nm film thickness.