Planar double heterostructures were initially investigated and have been successfully applied in III-V semiconductor lasers due to their excellent roles in confining both the photons and carriers. Here, we design and fabricate a (PEA)2Csn-1PbnX3n+1 (quasi-2D)/CsPbBr3 QD/quasi-2D double-heterostructure sandwiched in a 3/2 λ DBR microcavity, and then demonstrate a single-mode pure-green lasing with a threshold of 53.7 µJ/cm2 under nanosecond-pulsed optical pumping. The thresholds of these heterostructure devices decrease statistically by about 50% compared to the control group with no energy donor layers, PMMA/QD/PMMA in an identical microcavity. We show that there is efficient energy transfer from the barrier regions of the quasi-2D phases to the QD layer by transient absorption and luminescence lifetime spectra and that such energy transfer leads to marked threshold reduction. This work indicates that the double-heterostructure configurations should play a significant role in the future perovskite electrically pumped laser.
To explore the effect of surface charge properties of a photocatalyst on photocatalytic activity, quaternization TiO2 particles with different alkyl chain lengths (CT-X/P25) are first synthesized to boost the photocatalytic activity. The effect of a quaternary ammonium group with different alkyl chain lengths on the photocatalytic activity of CT-X/P25 is investigated. Interestingly, the introduction of a quaternary ammonium group on CT-X/P25 not only contributes to improving the photodegradation efficiency of anionic dyes due to enhancing of adsorption capacity through electrostatic attraction, but also it can improve the photodegradation efficiency of cationic dyes. Therefore, there seems to be another factor affecting the photocatalytic activity. The results of photoelectric characterization show that the photogenerated charge separation of CT-X/P25 is greatly enhanced, which is beneficial to improve the photocatalytic activity. Simultaneously, the results show that the difference in the photocatalytic activity of CT-X/P25 is mainly related to the charge intensity of -N+(CH3)2- in the quaternary amine salt. According to X-ray photoelectron spectroscopy, the charge intensity of -N+(CH3)2- in CT-X/P25 gradually increases with the increase in alkyl chain lengths, which is conducive to promoting photogenerated charge separation and improving the adsorption for anionic dyes. The photocatalytic activity has been further enhanced due to the enhancement of this synergy. In summary, the quaternary ammonium salt-modified CT-X/P25 shows an excellent synergistic effect on the process of photodegradation of anionic dyes: promoting photogenerated charge separation and adsorption.
CsPbCl3perovskite is an attractive semiconductor material with characteristics such as a wide bandgap, high chemical stability, and excellent optoelectronic properties, which broaden its application prospects for ultraviolet (UV) and violet photodetectors (PDs). However, large-area CsPbCl3films with high coverage, large grains, and controllable thickness are still difficult to prepare by using the solution method due to the extremely low solubility of their precursors in conventional solvents. Herein, a water-assisted confined re-growth method is developed, and a CsPbCl3microcrystalline film with an area of 3 cm × 3 cm is grown, the thickness of which is controllable within a range of several microns. The as-prepared thin film exhibits a flat and smooth surface, large grains, and enhanced photoluminescence. Furthermore, the fabricated violet PDs based on the prepared CsPbCl3film show a high responsivity of 2.17 A W-1, external quantum efficiency of 664%, on/off ratio of 2.58 × 103, and good stability. This study provides a prospective solution for the growth of large-area, large-grain, and surface-smooth CsPbCl3films for high-performance UV and violet PDs.
CsPbCl3 is an attractive wide-bandgap perovskite semiconductor. Herein, we have grown hopper-shaped CsPbCl3 crystals in a solution droplet dripped on a heated substrate. During the growth, we have observed the impacts of the coffee ring effect and Marangoni flow, which may result in the hopper shape. Their photoluminescence spectra feature double peaks, which are located at 413.9 nm and 422.0 nm, respectively, and the latter increases faster in intensity than the former as the excitation power increases. We believe that the higher-energy peak originates from the excitonic emission and the lower-energy one is from the polaritons' emission, where the polaritons are generated in the exciton-exciton inelastic scattering process. Based on such an explanation, the exciton binding energy of CsPbCl3 is estimated to be 76.7 meV in our experiments, consistent with the previous reports.
