Manipulating Exciton–Phonon Coupling to Optimize Carrier Properties for High-Performance 2D Perovskite Photodetectors

The charge transport properties of two-dimensional (2D) perovskites are crucial for high-performance optoelectronic devices, yet the relationship between their carrier dynamics and structural properties remains inadequately understood. This study demonstrates that the dielectric screening effect and structural rigidity of 2D perovskites, both governed by ligand properties, significantly modulate carrier transport by reducing exciton-phonon coupling. We synthesized 2D perovskites using linear, cyclic, and aromatic organic ligands. Among these, (3AMPY)PbI₄ (3AMPY = 3-(aminomethyl)pyridinium) exhibited the highest structural rigidity (Young's modulus ∼30.4 GPa) and relative dielectric constant (6.66). Increased rigidity resulting from multiple hydrogen bonds suppressed the lattice vibrations. The large dipole moment of the asymmetric structure (3AMPY) enhanced the dielectric screening effect, weakening localized interactions between electrons, holes, and phonons, further diminishing the exciton-phonon coupling to 134.8 meV. Consequently, the 3AMPY-based photodetector exhibited a responsivity of 0.97 A W^-1 and a high light on/off ratio exceeding 10⁵ under 532 nm illumination.