Impact of organic spacer cations on the light and thermal stability of two-dimensional lead halide perovskites

Long-term stability remains a critical challenge limiting the photovoltaic and optoelectronic applications of two-dimensional lead halide perovskites. In these materials, the choice of the organic spacer plays a key role not only in enhancing environmental stability, but also in determining their structural characteristics and carrier dynamics. Here, we present an environmental photo- and thermal-stability analysis of BA2PbI4 and PEA2PbI4 two-dimensional lead halide perovskites by means of confocal micro-Raman and X-ray photoelectron spectroscopy techniques. We have investigated two different organic spacers, n-butylammonium (BA) and 2-phenylethylammonium (PEA), which provide comparable room-temperature luminescence in freshly exfoliated perovskite nanoflakes and degrade similarly through the removal of organic components and fast crystal phase decomposition into PbI2 and Pb0. However, we observed that the PEA organic cation significantly improves crystal morphology and suppresses lattice defects, resulting in slower degradation and enhanced resistance to light and thermal stress under ambient conditions. Our findings indicate that structural and chemical engineering, along with surface passivation and encapsulation strategies, are essential for achieving long-term stability in two-dimensional halide perovskite devices. Nevertheless, optimizing the balance between stability and device performance remains a critical consideration.