Effects of Combining Dion-Jacobson and Ruddlesden-Popper Spacers on the Photophysics of Quasi-2D Perovskites

Quasi-2D lead-halide perovskites consist of conducting inorganic layers with tunable thickness (n) separated by large organic spacer cations. Typically, domains with different n and bandgaps are formed within a single film. Here, the crystallization of the films is tuned by mixing Dion-Jacobson (DJ) with Ruddlesden-Popper (RP) spacer cations. Compared to the quasi-2D perovskite film based on solely the DJ type spacer 1,4-phenylenedimethylammonium (PDMA), a film with less defects and more vertically aligned crystallization is achieved by addition of the RP type spacer propylammonium (PA). As the film structure plays an important role in the photophysics, time-resolved photoluminescence (TRPL) and femtosecond transient absorption (TA) are used to investigate the impact of mixing these spacer cations on the dynamics of hot carrier cooling, the occurrence and directionality of energy or electron transfer between the different domains, and the exciton and charge carrier dynamics. Exciton transfer from low-n to high-n domains occurs at a favorable faster rate for the PDMA-based film (0.0640 ps⁻¹) compared to the PA-based film (0.0365 ps⁻¹), while the mixed spacer film demonstrates intermediate behavior (0.0473 ps⁻¹). This study facilitates the design of advanced materials with optimized photophysical characteristics for a next generation of optoelectronic devices.