Gradient Dion-Jacobson Phase Stable Quasi-2D Perovskite@Graphene Hybrid for High Responsivity Photodetectors

Quasi-(2D) formamidinium lead-iodide (FAPbI₃) perovskites are winsome materials for high-performance photodetectors (PDs). Between Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, the latter exhibits lower non-radiative recombination and higher mobility compared to the relatively easily synthesized former. For efficient charge separation and transport, graphene-assisted two-terminal coplanar PD leveraging the DJ phase perovskite is proposed. Diamino octane (DAO), incorporated into 3D FAPbI₃ perovskite, resulted in DJ phase [DAO(FA)_n-1Pb_nI_3n+1], n being predefined integers 1≤ n ≤ ∞, demonstrating a vertical gradient heterostructure of n phases. Superior crystallinity and thermal stability of the quasi-2D films are confirmed via synchrotron-based studies. Band-edge of the 3D film blue-shifted consistently from 810 nm, while passing through the quasi-2D phases, to ≈500 nm for the 2D phase. The dynamic range of photoresponsivity (R) of PDs reflected the absorption trend, with the 2D perovskite being infrared blind. Graphene's high carrier mobility coupled with the perovskite's high absorbance resulted in an unprecedented high R of ≈10⁷ A W⁻¹ and specific detectivity of 9.77 × 10¹⁶ Jones under 42.25 nW cm⁻² of 405 nm illumination for the predefined n = 2 film. This underscores the potential of the DJ phase quasi-2D perovskite@graphene in realizing stable, sensitive, and spectrally tunable PDs.