Chain-Melting Temperature Depression in the Organic Layer of Two-Dimensional Perovskites

Two-dimensional (2D) perovskites with n-alkylammonium cations often undergo a solid-solid phase transition upon changes in pressure or temperature, during which the organic cations undergo an order-to-disorder chain-melting transition. Here, we show that blending halides and organic cations of varying lengths decreases the phase transition temperature of Cu- and Mn-based 2D perovskites. The magnitude of this decrease depends on the relative lengths of the two n-alkylammonium cations. For instance, blending n-decylammonium (DA) with n-undecylammonium (UDA) results in a 5 degrees C decrease in the phase transition temperature compared to pure DA2CuBr4. In contrast, blending DA with n-dodecylammonium (DDA) causes a 25 degrees C decrease. Furthermore, we found that blending Cu2+ and Mn2+ has a minimal effect on the phase transition temperature due to similar lattice spacing between the inorganic layers in DA2CuCl4 and DA2MnCl4. Our study suggests new design principles for tuning structural phase transitions in 2D perovskites through alloying halides, organic cations, and metal cations.