Surface‐Engineered Methylammonium Lead Bromide Single Crystals: A Platform for Fluorescent Security Tags and Photodetector Applications

Abstract

Surface/interface engineering of methylammonium lead bromide (MAPbBr3) single crystals (SCs) is crucial for carrier generation/recombination, separation, and transportation, thereby enabling superior optoelectronics. Herein, a surface‐engineered crystallization technique is presented in which a thin polycrystalline MAPbBr3 layer is in situ grown on the surface of bulk mm‐sized MAPbBr3 SCs. The growth direction and the atomic distribution of both the polycrystalline surface layer and the single crystalline core have been analyzed by damage‐free atomic‐resolution transmission electron microscopy (TEM). The polycrystalline nature of the crystals gives rise to bright green emission under UV light. Scanning probe microscopy results show that the current at the emissive MAPbBr3 film/MAPbBr3 SC surface is five times higher than that at a non‐emissive surface when illuminated. Lateral photodetectors based on MAPbBr3 film/MAPbBr3 SCs can achieve excellent detectivities (≈1013 Jones) and high photoresponsivities (≈20 A W−1). Furthermore, a semiconductor‐based fluorescence quick response (FQR) code is patterned on the same bright green‐emitting surface of the MAPbBr3 film/MAPbBr3 SC using a picosecond laser pulse, with a scalability of 3 × 3 mm2. An FQR code integrated with a photodetector may serve as a potential double security tag in bank cards, passports, door security, etc.

Improvement of Light Output of MAPbBr3 Single Crystal for Ultrafast and Bright Cryogenic Scintillator

“…In this study, we successfully grew high-quality transparent millimeter - sized MAPbBr 3 SCs, resulting in a bright green emission from the surface upon exposure to UV light. The detailed synthesis process was described in the previous work . Cathodoluminescence (CL) images demonstrated that THF-0.4M crystals exhibited enhanced luminescence signals, and photoluminescence (PL) measurements revealed a 10-fold increase in PL intensity compared to Control-1M MAPbBr 3 SCs.…”

“…Specifically, the THF-0.4M crystal demonstrates an increase of 2.4 times in comparison to the Control-1M crystal. The increase in RLY at cryogenic temperatures is linked to the increase of the modest quantum yield (2 times) and conductivity (almost 2 times) of the bulk crystals . The latter is strongly related to the transfer efficiency in the scintillation mechanism process .…”

“…Here we focus on 3D methylammonium lead bromide (MAPbBr 3 ) SCs, a subset of the perovskite SCs family that has gained considerable interest over the past few decades. Recently, we made significant and moderate improvements to the surface emission, quantum yield, and conductivity of the crystals, respectively . Now we have discovered that the two latter improvements also enhance the light yield (by 2 times) and decrease the decay time (to less than 1 ns) at 10 K. This ultrafast decay time positions MAPbBr 3 SCs among the fastest scintillators, surpassing other perovskite SCs in terms of decay components.…”

“…Also, the PL spectrum of the emissive surface is red-shifted about 5 nm with respect to that of the nonemissive crystals. However, although the PL intensity from the surface is significantly enhanced, the quantum yield of the bulk THF-0.4M crystal only improves 2-fold from 3% for the Control-1M crystal to 6% . The measured PL decay curves (Figure inset) show triple-exponential behaviors.…”

“…The detailed synthesis process was described in the previous work. 20 Cathodoluminescence (CL) images demonstrated that THF-0.4M crystals exhibited enhanced luminescence signals, and photoluminescence (PL) measurements revealed a 10-fold increase in PL intensity compared to Control-1M MAPbBr 3 SCs. To explore the luminescent and scintillation properties of a MAPbBr 3 (Control-1M and THF-0.4M) single crystal as a function of temperature, we used a 375 nm laser and X-rays.…”