Since the organic-inorganic halide perovskite was introduced as sensitizers for photovoltaic cells by Miyasaka et al., enormous amount of research effort goes into perovskite solar technology during the past five years. The excellent optical property and low cost process of organic-inorganic halide perovskite has attracted the world’s researchers’ attention, but few applied these materials to make laser devices [2,3]. Here we report on the fabrication and characteristics of the CH3NH3PbI3 perovskite thin film by a two-step low temperature solution process. To investigate the optical characteristics of the CH3NH3PbI3 thin film, we prepared a series of PbI2 film with different wet percentage wt% solvent, and cover with a 1 wt.% precursor solution of methylammonium iodide (CH3NH3I) in 2-propanol (IPA) at room temperature. Samples were mounted into a temperature controlled vacuum chamber and optically pumped by a third harmonic generation (THG) of Nd:YVO4 355 nm pulse laser at 77K. Incident beam was focused by a 100× near UV infinity-corrected objective lens with a numerical aperture (NA) of 0.55.The reflected light was collected into a 600 μm core UV optical fiber by the same objective lens and analysed by a 320 mm single monochromator with a spectral resolution of about 0.2 nm. We discovered that the formation of polycrystalline grain boundary provided random scattering paths for the optical feedback, thus the system can achieve the laser operation at a proper excitation power. The lasing characteristics of the thin film with 30 wt% PbI2 were shown in Fig. 1(a). The emission peak lased at 747 nm when the excitation power comes to 3.2 μW. The two-slope L-L curve of the lasing mode and the linewidth of the spectra reducing from 16 nm to 1 nm showed that the system achieved the laser operation, as shown in Fig. 1. To understand the optical properties of the fabricated perovskite thin film, we changed the temperature from 77K to 300K. Interestingly, the threshold power would gradually decrease from 77K to 120K and the trend reversed when we continued to increase the temperature from 120K to 300K. This could be due to the structural phase transition from orthorhombic to tetragonal crystalline structures during the temperature-increasing process. Furthermore, the formation of the perovskite thin film was influenced by the weight percent density of PbI2 and thereby affecting the lasing characterises of the devices. In summary our work presented a comprehensive investigation of optical characteristics on the solution processed organic-inorganic halide perovskite thin film, which can provide a useful guide line for making efficient and novel perovskite lasers in the near future.
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