Excited-state interactions between organic and inorganic components in hybrid metal halide semiconductors open up the possibility of moving charge and energy in deliberate ways, including energy funneling, triplet energy harvesting, or long-lived charge separation. In this work, we utilize π-conjugated naphthalene diimide electron accepting molecules to fabricate a hybrid one-dimensional (1D) lead iodide semiconductor ((NDIC2)Pb2I6) with an internal charge separating junction. Despite recent efforts on the synthesis of 1D metal halide semiconductors, little is known about their electronic structure, optical properties, and excited-state dynamics. Steady-state and time-resolved spectroscopy measurements of ((NDIC2)Pb2I6) thin films elucidate discrete optical features from the lead iodide and naphthalene diimide components of this heterostructure, along with a weakly bound optically active charge transfer state. The type-II heterojunction between the organic NDIC2 and inorganic Pb2I6 moieties facilitates rapid separation of photogenerated charges, where charge recombination is hindered by the spatial separation of charges across the organic/inorganic interface. Our study also provides some important insights into the ways in which Coulomb interactions between the organic and metal halide moieties and π–π interactions between the organic cations can affect the crystallization of these hybrid semiconductors with large, optically active π-conjugated chromophores. We believe our findings will further enable the rational design of low-dimensional organic–inorganic heterostructures where the dielectric environment, charge transfer states, and exciton behavior may be modulated.
(A) Pseudo-color image of the transient absorption (TA) spectra for (NDI)Pb2I6 thin film. The horizontal and vertical axes are the probe-photon wavelength and pump–probe delay, respectively. The color intensity indicated by the scale bar represents the TA signal magnitude. (B-C) The TA spectra at different time delay for (B) (NDI)Pb2I6 and (C) NDIC2-I2 films. (D) Decay dynamics of (NDI)Pb2I6 thin film probed at photo-induced absorption (PIA) peak at 540nm and photo-bleach peak (PB) at 400nm.
Read the full article at Journal of Materials Chemistry A
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