Role of Polycyclic Aromatic Alkylammonium Cations in Tuning the Electronic Properties and Band Alignment of Two-Dimensional Hybrid Perovskite Semiconductors

Abstract

Two-dimensional hybrid organic−inorganic perovskites (HOIPs) have recently drawn intense attention as potential photovoltaic materials. However, n = 1 two-dimensional (2D) HOIPs face the challenge of low conductivity between the inorganic layers, leading to unsatisfactory device performance. Interestingly, 2D HOIPs employing π-conjugated molecules as organic moieties show energy and charge transfers between organic and inorganic layers, indicating potentially efficient carrier transport for photovoltaic applications. Nevertheless, the development of 2D HOIP-based solar cells especially utilizing polycyclic aromatic alkylammonium as cations is in its infancy. Herein, we investigated the electronic structure and band alignment of a series of n = 1 2D Ruddlesden−Popper (RP) phase HOIPs containing different polycyclic aromatic groups and alkyl chains, based on density functional theory calculations. We find that the polycyclic aromatic group plays an important role in controlling the functionality of 2D HOIPs by directly modifying band-edge states, and the band alignment at the organic−inorganic interface can be designed to promote either exciton trapping or dissociation for light-emitting or photovoltaic applications, respectively.

Two Dimensional Perovskites/Transition Metal Dichalcogenides Heterostructures: Puzzles and Challenges

“…Adapted with permission from. [111] Copyright 2021 American Chemical Society. (e) Scheme of alkyl linkers and aromatic groups in (aromatic-O-linker-NH 3 ) 2 PbI 4 used for the calcualations presented in panel (d).…”

“…The band edges belonging to the organic and inorganic components are shown in blue and red, respectively. Adapted with permission from [111] . Copyright 2021 American Chemical Society.…”

“…(e) Scheme of alkyl linkers and aromatic groups in (aromatic‐O‐linker‐NH 3 ) 2 PbI 4 used for the calcualations presented in panel (d). Adapted with permission from [111] . Copyright 2021 American Chemical Society.…”

“…Most of the works on 2DPs focused on organic cations that contain alkyl chains or single‐ring conjugated molecules (such phenylethylammonium, PEA), which have relatively large energy gaps favoring a type I b band alignment. Nevertheless, recent theoretical and experimental work suggests that all four band alignment types can be achieved with the use of appropriately long or large π ‐conjugated molecules [64,111,127–132] . Moreover, the band alignment can also be controlled with the use of different halide atoms (I, Br, Cl) opening or closing the band gap of the inorganic component [64] …”

“…Nevertheless, recent theoretical and experimental work suggests that all four band alignment types can be achieved with the use of appropriately long or large π-conjugated molecules. [64,111,[127][128][129][130][131][132] Moreover, the band alignment can also be controlled with the use of different halide atoms (I, Br, Cl) opening or closing the band gap of the inorganic component. [64] The possibility to selectively control the spatial localization of electrons and holes potentially gives yet another tool to promote the transfer of charges from the 2DP layer to the TMD layer.…”