Mixed-Solvent Crystallization Expands the Chemical Space of 2D Perovskites and Enables Phonon-Limited Exciton Transport

The advancement of two-dimensional (2D) halide perovskite
optoelectronics
relies on synthetic methods that enable new material discovery and
the growth of high-quality crystals with a low defect density. Despite
the vast chemical space of potential organic cations, many remain
incompatible with conventional aqueous solution synthesis, which leads
to thermodynamically stable non-2D-perovskite structures or introduces
chemical reactivity issues. Here, we present a room-temperature evaporation-induced
crystallization approach using a mixed organic–aqueous solvent
system for the exploratory synthesis of 2D perovskites. This method
is compatible with an extended range of organic cations, enabling
the facile discovery of 25 new 2D perovskites, including 16 that are
either kinetically stable or inaccessible with the conventional method.
The expanded 2D perovskite library reveals the critical role of intermolecular
interactions between the organic cations in stabilizing the kinetically
stable 2D perovskite structures. Moreover, the as-grown crystals exhibit
near-intrinsic free exciton emission with significantly reduced defect
emissions and exciton diffusion coefficients enhanced by up to 5-fold,
approaching the intrinsic transport limits governed by exciton–phonon
scattering. This work not only broadens the design space of organic
cations for 2D perovskites but also establishes a general synthetic
strategy for growing high-quality 2D perovskite crystals, which are
essential for high-performance optoelectronics.