Optical contrast and photoluminescence study of two-dimensional lead iodide perovskite stability to ambient conditions
Marie Krecmarova a, Rodolfo Canet-Albiach a, Jesús Rodríguez-Romero b, Iván Mora-Seró b, Juan P. Martínez-Pastor a, Juan F. Sánchez-Royo a
a Institute of Materials Science of the University of Valencia (ICMUV), Spain
b Universitat Jaume I, Institute of Advanced Materials (INAM) - Spain, Avinguda de Vicent Sos Baynat, Castelló de la Plana, Spain
Poster, Marie Krecmarova, 046
Publication date: 23rd April 2020

Two-dimensional (2D) lead halide perovskites hold great promise for fabrication of novel optoelectronic devices. However, their chemical stability to environmental conditions is still a critical issue for their commercial applications. In this work, we focus on 2D lead iodide perovskites (n=1,2) crystals stability study by optical contrast (OC) and photoluminescence (PL). The several 2D perovskites crystals were mechanically exfoliated onto SiO2/Si substrate and monitored during 3 months at air environment with simultaneous exposure to different surrounding conditions: 1) daylight at room temperature (T), 2) dark (room T), 3) dark (~ 4° C) and 4) laser illumination (as exfoliated). Moreover, degradation of partially protected crystals with hexagonal boron nitride (hBN) was also studied.  First, we demonstrate the ability of OC technique for degradation study of 2D perovskites. The OC exhibits a linear trend up to ~6 mono-layers, nevertheless degradation of thicker crystals can be also monitored by change of OC. From our investigations follow than crystals exposed to daylight degraded already within a week, crystals stored in dark at room T degraded within 3 months, surprisingly crystals stored in dark and at lower temperature of ~ 4° C shows the best stability without significant degradation within 3 months. Then we investigated green laser illumination degradation of crystals by OC and PL as function of laser power and illumination time. OC reveals the creation of holes in the sample that deeps into the sample with simultaneous visible degradation around all over the crystal area. The OC data are supported with PL measurements indicating loss of PL activity at high laser power. Note, that thinner crystals degrade faster than a thicker one. Finally, we partially covered the 2D perovskite crystals by few-layer thick hBN and studied their degradation for 3 months and also by laser illumination. The protected perovskite crystals show longer-term stability than unprotected one and also resistance to a higher laser power irradiation (no holes were observed at protected areas). We verified that the OC technique is fast and non-invasive for the monitoring of the crystal degradation, which is even not clearly visible by eye.

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