Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites

Understanding the effect of organic spacers on the fundamental excited-state processes in 2D perovskites is crucial for advancing these novel materials. Herein, we study these processes for manganese (Mn)-doped 2D Ruddlesden-Popper perovskites with aromatic phenethylammonium (PEA) and aliphatic butylammonium (BA) spacer ligands. Mn-doping offers a powerful strategy for tuning and enhancing the optoelectronic properties of halide perovskites. Despite notable advancements, the Mn-based emission dynamics and the spacer’s influence on the doping mechanism remain poorly understood. We explore Mn-doped 2D perovskites by varying the organic spacer and Mn molar fraction, examining nanoplatelets, and bulk crystals. We observe a complete substitution of Mn ²⁺ ions at the crystals’ edges at high doping levels, and a uniform distribution at lower ones, for both spacers. Yet, the Mn-emission differs significantly based on the spacer. PEA-based perovskites exhibit strong emission with a photoluminescence quantum yield of 75%, dropping to 57% for BA. To uncover this contrast, we probed exciton transport using transient reflection microscopy, revealing nearly twice the exciton diffusivity in PEA compared to BA. We further correlate crystal rigidity and exciton–phonon coupling with diffusivity. This work offers a general framework for studying spacer effects in 2D perovskites, guiding the design of advanced luminescent materials.