Radiation Tolerance and Defects Activity in Metal Halide Perovskite Single Crystals

Metal halide perovskites (MHPs) are low-temperature processable hybrid semiconductor materials with exceptional performances that are revolutionizing the field of optoelectronic devices. Despite their great potential, commercial deployment is hindered by MHPs lack of stability and durability, mainly attributed to ions migration and chemical interactions with the device electrodes.<br/> <br/>The presence of electronic trap states has been a tough challenge in terms of characterization and thus mitigation. Many attempts based on electronic spectroscopies have been tested, but due to the mixed electronic-ionic nature of MHPs conductivity, many experimental results retain a large ambiguity in resolving electronic and ionic charge contributions. Here we adapt a method, previously used in highly resistive inorganic semiconductors, called photo-induced current transient spectroscopy (PICTS) on lead bromide 2D-like ((PEA)2PbBr4) and standard “3D” (MAPbBr3) MHPs single crystals. We present two conceptually different outcomes of the PICTS measurements, distinguishing the different electronic and ionic contributions to the photocurrents, based on the different ion drift of the two materials. Our experiments unveil deep levels trap states on the 2D, “ion-frozen” (PEA)2PbBr4 and set new boundaries for the applicability of PICTS on 3D MHPs [1].<br/> <br/>We focus our attention on 2D layered MHPs, recently reported as very promising candidate for the direct detection of X-rays, with superior radiation resilience if compared to standard "3D" perovskites [2]. The physical mechanisms responsible for such improvement are still not fully understood, possibly associated the peculiar charge transport process in PEA2PbBr4 crystals<br/> <br/>We demonstrate that PICTS can detect three distinct trap states (T1, T2, and T3) with different activation energies, and that the trap states evolution upon X-ray exposure can explain PEA2PbBr4 superior radiation tolerance and reduced aging effects [3]. Overall, our results provide essential insights into the stability and electrical characteristics of Metal Halide perovskites and on the great potential of 2D perovskites in applications where reliable and highly radiation tolerant active materials are needed.<br/> <br/> <br/>REFERENCES<br/>[1] G.Armaroli, L.Maserati, A. Ciavatti, P.Vecchi, A.Piccioni, M.Foschi, V.Van der Meer, C. Cortese, M.Feldman, V.Foderà, T.Lemercier, J.Zaccaro, J.Guillén, E.Gros-Daillon, B.Fraboni, and D. Cavalcoli ACS Energy Letters 2023 8 (10), 4371-4379<br/>[2] Lédée, A. Ciavatti, M. Verdi, L. Basiricò, and B. Fraboni, “Ultra-Stable and Robust Response to X-Rays in 2D Layered Perovskite Micro-Crystalline Films Directly Deposited on Flexible Substrate,” Advanced Optical Materials 10(1), 2101145 (2022).<br/>[3] A.Ciavatti, V.Foderà, G.Armaroli, L.Maserati, B.Fraboni, D.Cavalcoli 2024 under revision