Asymmetric Diammonium Directed In-Plane Charge Transport Enhancement in Two-Dimensional Lead Bromide Perovskite for Weak-Light Detection.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites are drawing significant attention in optoelectronic fields because of their enhanced out-of-plane electron coupling and improved structure stability. However, the structural effects of organic cations on the in-plane charge transport properties of 2D DJ lead bromide perovskites have remained less explored. Herein, we adopt asymmetric 3-(dimethylamino)-1-propylammonium (DMPD) and symmetric butane-1,4-diammonium (BDA) to systematically investigate the influence of organic cations on the structural, optical, and in-plane charge transport properties of 2D lead bromide perovskites. The large penetration depth of DMPD 2+ induces a decreased perovskite layer distortion and a lower bandgap in DMPDPbBr 4 , compared with that of BDAPbBr 4 . Moreover, DMPDPbBr 4 is shown to possess a low exciton binding energy, a low defect density, and a low ion migration activation energy, thereby yielding a more efficient in-plane charge collection efficiency than BDAPbBr 4 . Density functional theory calculations suggest that the improved in-plane charge transport can be traced to the enlarged antibonding coupling between Pb-6s and Br-4p orbitals that enables a high band dispersion and a low carrier effective mass in the in-plane direction of DMPDPbBr 4 . Finally, the planar Ag/DMPDPbBr 4 /Ag photodetector delivers a satisfying detectivity of 1.73 × 10 12 Jones under an incident power intensity of 0.16 mW cm -2 and a high on/off ratio of 5.3 × 10 3 . The above findings offer novel insight for the design of 2D DJ lead bromide perovskites for optoelectronic devices.