Instability of two-dimensional hybrid perovskites underpinned by organic molecule loss under light illumination

Two-dimensional (2D) organic-inorganic hybrid perovskites have emerged as a promising class of photovoltaic and optoelectronic materials. However, instability induced by external stimuli, particularly light, limits their applications. Here, we have systematically investigated the photostability in a series of (BA)₂(MA)_n−1Pb_nBr_3n+1 (n = 1, 2, and 3) samples via multimodal characterization combining both microscopy and spectroscopy. Samples with all three compositions exhibit a similar photodegradation mechanism, with higher photostability observed in higher n samples. By explicitly detecting the loss of BA and MA molecules driven by light illumination and quantitatively measuring their loss rates, we identified faster loss of BA molecules compared with MA, both occurring preferentially at the sample edges and surface cracks and leading to the collapse of the BA layers with a reduced sample thickness and intrinsic emission. Eventually all samples degrade into the transparent PbBr₂ with an amorphous structure, which propagates gradually to the inside without altering the 2D shape of sample flakes. Our work not only advances the understanding of photostability of 2D perovskites, but also demonstrates a powerful characterization approach to quantitatively measure degradation kinetics associated with organic molecule loss in various hybrid perovskites.