Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.
Nonequilibrium processes occurring in functional materials can significantly impact device efficiencies and are often difficult to characterize due to the broad range of length and time scales involved. In particular, mixed halide hybrid perovskites are promising for optoelectronics, yet the halides reversibly phase separate when photo-excited, significantly altering device performance. By combining nanoscale imaging and multiscale modeling, we elucidate the mechanism underlying this phenomenon, demonstrating that local strain induced by photo-generated polarons promotes halide phase separation and leads to nucleation of light-stabilized iodide-rich clusters. This effect relies on the unique electromechanical properties of hybrid materials, characteristic of neither their organic nor inorganic constituents alone. Exploiting photo-induced phase separation and other nonequilibrium phenomena in hybrid materials, generally, could enable new opportunities for expanding the functional applications in sensing, photoswitching, optical memory, and energy storage.Photovoltaic and light-emitting devices typically operate under conditions far from equilibrium. As such, elucidating the response of functional materials to nonequilibrium driving forces is vital to understanding their fundamental properties and to determining their suitability for device applications. In particular, photo-induced dynamic processes are of major importance to the performance of hybrid perovskite-based devices.1-3 Hybrid perovskites are low-cost, solution processable materials that are promising for many device applications, including photovoltaics 4-9 and light-emitting diodes (LEDs). 10The high device efficiencies have been attributed to their high brightness, long charge carrier migration lengths, + 2 , FA), and X is either iodide, bromide, chloride, or iodide/bromide or bromide/chloride mixtures. By varying the halide ratios in hybrid perovskites, the bandgap can be tuned across the visible spectrum.1,14,15 Precise control of the bandgap presents promising opportunities for color tuning perovskite-based LEDs and lasers, and for incorporating hybrid perovskites in tandem solar cells. 9,16Light-induced effects, however, restrict the practical use of mixed halide hybrid perovskites.1,17,18 Photoluminescence (PL) and X-ray diffraction (XRD) measurements suggest that MAPb(I x Br 1−x ) 3 (0.1 < x < 0.8) undergoes reversible phase separation into iodide-rich and bromiderich regions when photo-excited.1 Such demixing is detrimental to photovoltaic performance, since it leads to charge carrier trapping in the iodide-rich regions. Determining the microscopic mechanism behind phase separation is essential for furthering approaches to mitigate adverse photo-induced effects in devices and should expand the range of their functional applications into areas such as optical memory storage and sensing.19,20 Unfortunately, the microscopic mechanism behind this effect has been elusive because of the multiple length and time scales involved in characterizing the ...
We study poly(3-{[2-(2-methoxyethoxy)ethoxy]methyl}thiophene-2,5-diyl) (P3MEEMT), a new polythiophene derivative with ethylene glycol-based side chains, as a promising semiconducting polymer for accumulation-mode organic electrochemical transistors (OECTs) with figures of merit comparable to those of state-of-the-art materials. By characterizing the OECT performance of P3MEEMT transistors as a function of the anion, we find that large hydrophobic anions lower the threshold voltage. We find that, compared to poly(3-hexylthiophene-2,5-diyl) (P3HT), P3MEEMT has faster anion injection rates, which we attribute to the hydration of the P3MEEMT crystal lattice. We study P3MEEMT-based OECT and organic field-effect transistor (OFET) performance as a function of film crystallinity and show that changing the crystallinity of the polymer by thermal annealing increases the OFET mobility yet decreases the OECT mobility. We attribute this difference to the fact that, unlike OFETs, OECTs operate in aqueous environments. To probe how hydration affects the operation of OECTs, we investigate the role of water in electrochemical doping using electrochemical quartz microbalance (EQCM) gravimetry. We find that steady-state hydration and hydration dynamics under electrochemical bias differ dramatically between the crystalline and amorphous P3MEEMT films. These results suggest that the presence of water reduces the electronic connectivity between the crystalline regions of P3MEEMT, thus lowering the mobility in solution. Overall, our study highlights the importance of the role of polymer hydration and nanoscale morphology in elucidating design principles for OECT operation.
Halide perovskites are promising semiconductor materials for solutionprocessed optoelectronic devices. Their strong ionic bonding nature results in highly dynamic crystal lattices, inherently allowing rapid ion exchange at the solid-vapor and solid-liquid interface. Here, we show that the anion-exchange chemistry can be precisely controlled in single-crystalline halide perovskite nanomaterials when combined with nanofabrication techniques. We demonstrate spatially resolved multicolor CsPbX 3 (X = Cl, Br, I, or alloy of two halides) nanowire heterojunctions with a pixel size down to 500 nm with the photoluminescence tunable over the entire visible spectrum. In addition, the heterojunctions show distinct electronic states across the interface, as revealed by Kelvin probe force microscopy. These perovskite heterojunctions represent key building blocks for high-resolution multicolor displays beyond current state-of-the-art technology as well as high-density diode/transistor arrays.nanowire | halide perovskite | anion exchange | heterojunction S ignificant research efforts are currently directed toward lead halide-based perovskites, owing to their unusual optoelectronic and photovoltaic properties (1-5). In addition to polycrystalline thin films, various solution-based synthetic routes toward low-dimensional nanostructures of halide perovskites have been recently demonstrated, with control over size, shape, mixed halide composition, and consequently their band gap and emission wavelength (6-10). Interestingly, it has been shown that these materials, both in bulk and in nanocrystalline form, can undergo fast anion-exchange reactions at the solid-liquid or solid-gas interface, with a fine-tuning of the chemical composition and electronic properties (11)(12)(13)(14). The fast ion-exchange kinetics in halide perovskite are related to the low defect formation energy and the existence of a large number of vacancies, which make the ions highly mobile in the crystal lattice (15). As a result, the anionexchange reaction in halide perovskites favors forming homogeneous alloys instead of any kind of heterostructures as commonly observed in II-VI semiconductor compounds. If the exchange reaction can be localized at particular positions, then it is possible to produce substrates with well-defined patterns of semiconductor heterojunctions (16)(17)(18)(19)(20). The physical properties (optical, electrical, magnetic, etc.) of the heterostructure are fundamentally interesting, and the patterned semiconductor heterojunctions are essential for the fabrication of large-scale high-density integrated electronic and photonic devices.Compared with perovskite polycrystalline thin films and quantum dots, single-crystalline nanowires provide an ideal platform for producing and studying heterojunctions via ion-exchange chemistry because of the absence of grain boundaries and the unique one-dimensional geometry (21-24). The relatively thin diameter of the nanowire ensures rapid ion exchange in the radial direction, whereas the micrometer scale l...
Facile ionic transport in lead halide perovskites plays a critical role in device performance. Understanding the microscopic origins of high ionic conductivities has been complicated by indirect measurements and sample microstructural heterogeneities. Here, we report the direct visualization of halide anion interdiffusion in CsPbCl3–CsPbBr3 single crystalline perovskite nanowire heterojunctions using wide-field and confocal photoluminescence measurements. The combination of nanoscale imaging techniques with these single crystalline materials allows us to measure intrinsic anionic lattice diffusivities, free from complications of microscale inhomogeneity. Halide diffusivities were found to be between 10−13 and ∼10−12 cm2/second at about 100 °C, which are several orders of magnitudes lower than those reported in polycrystalline thin films. Spatially resolved photoluminescence lifetimes and surface potential measurements provide evidence of the central role of halide vacancies in facilitating ionic diffusion. Vacancy formation free energies computed from molecular simulation are small due to the easily deformable perovskite lattice, accounting for the high equilibrium vacancy concentration. Furthermore, molecular simulations suggest that ionic motion is facilitated by low-frequency lattice modes, resulting in low activation barriers for vacancy-mediated transport. This work elucidates the intrinsic solid-state ion diffusion mechanisms in this class of semisoft materials and offers guidelines for engineering materials with long-term stability in functional devices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.