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

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 (approximate to 1013 Jones) and high photoresponsivities (approximate to 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 x 3 mm2. An FQR code integrated with a photodetector may serve as a potential double security tag in bank cards, passports, door security, etc. This study optimizes in-situ formation of a thin polycrystalline MAPbBr3 layer on bulk MAPbBr3 single crystals with intense surface green emission under UV light. Utilizing this, a semiconductor-based fluorescent quick response (QR) code integrated with a photodetector is developed, presenting potential for highly efficient dual security tags in applications like bank cards, passports, and door security systems, among others. image