The preparation of wide-gap CsPbCl3 thin films from solution is impeded by the poor concomitant solubility of the precursor salts PbCl2 and CsCl. In the present study, we prepared superlattices of PbCl2 and CsCl by thermal evaporation. The superlattice shows an intense photoluminescence at 413 nm with a narrow line width of 10 nm (FWHM), which agrees with reports of CsPbCl3 single crystals. Most notably, the resulting layer structures support amplified spontaneous emission (ASE) in the deep blue spectral region at 427 nm (width 2.2 nm) under pulsed optical excitation (355 nm, 300 ps) above a threshold energy density of 190 μJ/cm2 at room temperature (RT). This is the first report of CsPbCl3 thin films showing ASE at RT.
Halide perovskites are currently of interest for a variety of optoelectronic applications. While, typical wet-chemical preparation techniques afford relatively rough polycrystalline layers, we have recently demonstrated that thermal imprint is a powerful post-deposition processing tool that affords extremely smooth perovskite thin-films with crystals that extend over tens of microns laterally.[1,2] A comparative study of optical, morphological and thermal properties (e.g. thermal conductivity) reveals some striking similarity of pressed MAPbX3 thin-films and their single crystalline analogues. More recently, we successfully used thermal imprint also for entirely inorganic halide perovskite materials, such as CsPbBr3. While as-deposited CsPbBr3 layers are typically discontinuous and rough with a large number of pinholes, thermal imprint at relatively low temperature and pressure (150°C, 100 bar) will be shown to turn them into dense, smooth and pinhole-free thin films, which show substantially enhanced luminescence quantum yield and in contrast to pristine CsPbBr3 layers even enable room-temperature amplified spontaneous emission (ASE). Perovskite thin films patterned by thermal nanoimprint with photonic resonator structures will be shown to afford hybrid and entirely inorganic distributed feedback lasers, with ultra-low lasing thresholds.[2,4]
 A. Mayer et al. J. Vac. Sci. & Techol. B 2017, 35, 06G803.
 N. Pourdavoud et al. Adv. Mater. Technol. 2018, 3, 1700253.
 R. Heiderhoff et al. J. Phys. Chem. C 2017, 121, 28306.
 N. Pourdavoud et al. Adv. Mater. 2017, 29, 1605003.