Sn(II)-based halide perovskite semiconductor materials are promising for a variety of electronics and optoelectronics applications but suffer from poor intrinsic materials stability. Here, we report the synthesis and characterization of a stable Sn (II)-based two-dimensional perovskite featuring a π-conjugated oligothiophene ligand, namely (4Tm) 2 SnI 4 , where 4Tm is 2-(3″′,4′-dimethyl-[2,2′:5′,2″:5″,2″′-quaterthiophen]-5-yl)ethan-1-ammonium. The conjugated ligands facilitate formation of micrometer-size large grains, improve charge injections, and stabilize the inorganic perovskite layers. Thin film field-effect transistors based on (4Tm) 2 SnI 4 exhibit enhanced hole mobility up to 2.32 cm 2 V −1 s −1 and dramatically improved stability over the previous benchmark material (PEA) 2 SnI 4 . Stabilization mechanisms were investigated via single-crystal structure analysis as well as density functional theory calculations. It was found that the large conjugated organic layers not only serve as thick and dense barriers for moisture and oxygen but also increase the crystal formation energy via strong intermolecular interactions. This work demonstrates the great potential of molecular engineering for organic−inorganic hybrid perovskite materials toward applications in high-performance electronics and optoelectronics.

Two-dimensional perovskites that could be regarded as natural organic–inorganic hybrid quantum wells (HQWs) are promising for light-emitting diode (LED) applications. High photoluminescence quantum efficiencies (approaching 80%) and extremely narrow emission bandwidth (less than 20 nm) have been demonstrated in their single crystals; however, a reliable electrically driven LED device has not been realized owing to inefficient charge injection and extremely poor stability. Furthermore, the use of toxic lead raises concerns. Here, we report Sn­(II)-based organic–perovskite HQWs employing molecularly tailored organic semiconducting barrier layers for efficient and stable LEDs. Utilizing femtosecond transient absorption spectroscopy, we demonstrate the energy transfer from organic barrier to inorganic perovskite emitter occurs faster than the intramolecular charge transfer in the organic layer. Consequently, this process allows efficient conversion of lower-energy emission associated with the organic layer into higher-energy emission from the perovskite layer. This greatly broadened the candidate pool for the organic layer. Incorporating a bulky small bandgap organic barrier in the HQW, charge transport is enhanced and ion migration is greatly suppressed. We demonstrate a HQW-LED device with pure red emission, a maximum luminance of 3466 cd m–2, a peak external quantum efficiency up to 3.33%, and an operational stability of over 150 h, which are significantly better than previously reported lead-free perovskite LEDs.

Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better phase control. We demonstrate that extending the π-conjugation length and increasing the cross-sectional area of the ligand enables perovskite thin films with dramatically suppressed ion transport, narrowed phase distributions, reduced defect densities, and enhanced radiative recombination efficiencies. Consequently, we achieved efficient and stable deep-red light-emitting diodes with a peak external quantum efficiency of 26.3% (average 22.9% among 70 devices and cross-checked) and a half-life of ~220 and 2.8 h under a constant current density of 0.1 and 12 mA/cm2, respectively. Our devices also exhibit wide wavelength tunability and improved spectral and phase stability compared with existing perovskite light-emitting diodes. These discoveries provide critical insights into the molecular design and crystallization kinetics of low-dimensional perovskite semiconductors for light-emitting devices.

Controlling grain growth is of great importance in maximizing the charge carrier transport for polycrystalline thin-film electronic devices. The thin-film growth of halide perovskite materials has been manipulated via a number of approaches including solvent engineering, composition engineering, and post-treatment processes. However, none of these methods lead to large-scale atomically flat thin films with extremely large grain size and high charge carrier mobility. Here, we demonstrate a novel π-conjugated ligand design approach for controlling the thin-film nucleation and growth kinetics in twodimensional (2D) halide perovskites. By extending the π-conjugation and increasing the planarity of the semiconducting ligand, nucleation density can be decreased by more than 5 orders of magnitude. As a result, wafer-scale 2D perovskite thin films with highly ordered crystalline structures and extremely large grain size are readily obtained. We demonstrate high-performance field-effect transistors with hole mobility approaching 10 cm 2 V −1 s −1 with ON/OFF current ratios of ∼10 6 and excellent stability and reproducibility. Our modeling analysis further confirms the origin of enhanced charge transport and field and temperature dependence of the observed mobility, which allows for clear deciphering of the structure−property relationships in these nascent 2D semiconductor systems.

A timely review of recent exciting progress is provided regarding the molecular design, optical characterization, and device fabrications of novel 2D halide perovskite materials incorporating functional organic semiconducting building blocks.