Tuning the Optical Properties of CsPbBr3 Nanocrystals by Anion Exchange Reactions with CsX Aqueous Solution

Ultrafast electron shuttling suppresses the energy transfer process in Mn-doped CsPbCl3 nanocrystals

Taking advantage of the slow exciton-to-dopant energy transfer process, we dissociated the exciton in Mn-doped perovskite via ultrafast electron shuttling to a surface adsorbed 4-nitro phenol molecule. The observed ultrafast electron transfer process is competitive to the ultrafast exciton scattering process (∼140 fs) to the continuum states via optical phonons, but three-orders faster than the exciton-to-Mn energy transfer timescale.

Unraveling the Relevance of Electron and Hole Transfer in Lead Halide Perovskite Nanocrystals on Current Conduction

Optimization of perovskite-based optoelectronic performance demands prudent engineering in the device architecture with facile transport of generated charge carriers. Herein, we explore the charge transfer (CT) kinetics in perovskite nanocrystals (PNCs), CsPbBr3, with two redox-active quinones, menadione (MD) and anthraquinone (AQ), and its alteration in halide exchanged CsPbCl3. With a series of spectroscopic and microscopic measurements, we infer that both electron and hole transfer (ET-HT) prevail in CsPbCl3 with quinones, resulting in a faster CT, while ET predominates for CsPbBr3. Furthermore, current-sensing atomic force microscopy measurements demonstrate that the conductance across a metal-PNC-metal nanojunction is improved in the presence of quinones. The contributions of ET and HT to current conduction across PNCs are well supported and validated by theoretical calculations of the density of states. These outcomes convey a new perspective on the relevance of ET and HT in the optimal current conduction and optoelectronic device engineering of perovskites.

In-situ growth of low-dimensional perovskite-based insular nanocrystals for highly efficient light emitting diodes

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices. However, judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology, composition, and defect. Herein, we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization. The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX₃ perovskite, respectively. The formation of supramolecular structure retard perovskite nucleation, while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth. This judicious control enables a segmented growth, inducing the growth of insular nanocrystal consist of low-dimensional structure. Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%, ranking among the highest efficiency achieved. The homogeneous nano-island structure also enables high-efficiency large area (1 cm²) device up to 21.6%, and a record high value of 13.6% for highly semi-transparent ones.

Biaxial strain improving carrier mobility for inorganic perovskite:ab initioBoltzmann transport equation

Inorganic halide perovskites have attracted interest due to their high efficiency and low cost. Considering the uncertainty of experimental measurements, it was important to predict the upper limit of carrier mobility. In this study, theab initioBoltzmann transport equation, including all electron-phonon interactions, was used to accurately predict the mobilities of CsPbI₃, CsSnI₃, CsPbBr₃, and CsSnBr₃. Using the iterative Boltzmann transport equation (IBTE), the calculated mobility for CsPbI₃isµ_e= 512/µ_h= 379 cm² V^-1 s^-1, and Sn-based perovskite exhibited high hole mobility. The longitudinal optical phonons associated with the stretching between halogen anions and divalent metal cations were revealed to be the dominant scattering source for the carriers. Furthermore, the effect of biaxial strain on mobility was investigated. We observed that biaxial compressive strain could improve the mobility of CsPbI₃and CsPbBr₃. Surprisingly, under a compressive strain of-2%, the mobilities of CsPbI₃using IBTE approach were improved toµ_e= 1176/µ_h= 936 cm² V^-1 s^-1. It was revealed that the compressive strain could decrease the effective mass of CsPbI₃and CsPbBr₃.

Förster Resonance Energy Transfer Assisted Enhancement in Optoelectronic Properties of Metal Halide Perovskite Nanocrystals

Regulated excited state energy and charge transfer play a pivotal role in nanoscale semiconductor device performance for efficient energy harvesting and optoelectronic applications. Herein, we report the influence of Förster resonance energy transfer (FRET) on the excited-state dynamics and charge transport properties of metal halide perovskite nanocrystals (PNCs), CsPbBr₃, and its anion-exchanged counterpart CsPbCl₃ with CdSe/ZnS quantum dots (QDs). We report a drop in the FRET efficiency from ∼85% (CsPbBr₃) to ∼5% (CsPbCl₃) with QDs, inviting significant alteration in their charge transport properties. Using two-probe measurements we report substantial enhancement in the current for the blend structure of PNCs with QDs, originating from the reduced trap sites, compared to that of the pristine PNCs. The FRET-based upshot in the conduction mechanism with features of negative differential resistance and negligible hysteresis for CsPbBr₃ PNCs can add new directions to high performance-based photovoltaics and optoelectronics.

All-in-One Process for Color Tuning and Patterning of Perovskite Quantum Dot Light-Emitting Diodes

Although post-synthetic anion exchange allows halide perovskite quantum dots to easily change the optical bandgap of materials, additional exchange of shorter ligands is required to use them as active materials in optoelectronic devices. In this study, a novel all-in-one process exchanging ligands and halide anions in film-state for facile color tuning and patterning of cesium lead halide perovskite colloidal quantum dot (PeQD) light-emitting diodes (LEDs) is proposed. The proposed all-in-one process significantly enhances the performances of PeQD LEDs by passivating the PeQD with shorter ligands. In addition, the all-in-one process is repeated more stably in the film state. Red, green, and blue LEDs with extremely narrow emission spectra using cesium lead bromide PeQDs and appropriate butylammonium halide solutions are fabricated. Furthermore, the proposed all-in-one process in film-state facilitated rapid color change in localized areas, thereby aiding in realizing fine patterns of narrow widths (300 µm) using simple contact masks. Consequently, various paint-over red/green/blue patterns in PeQD LEDs by applying halide solutions additively are fabricated.

A Study on Improving the Sensitivity of Indirect X-ray Detectors by Adding Hybrid Perovskite Quantum Dots

In this paper, we demonstrate the enhancement in detection sensitivity of an indirect X-ray detector based on poly(3-hexylthiophene) (P3HT) and fullerene derivatives [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) by adding perovskite quantum dots (PeQDs). The weight ratio of P3HT and PC71BM was fixed at 1:1 (20 mg/mL in chlorobenzene), and different amounts of FAPbBr3 PeQDs of (0–3) mg were added to the P3HT:PC71BM active layer solution. The experimental results show that the detector using P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) achieved a sensitivity of 2.10 mA/Gy∙cm2. To further improve the sensitivity, a ligand exchange experiment was performed on the P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) detector. Under the condition of 12 h ligand exchange time, the detector with P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) showed the highest sensitivity of 2.26 mA/Gy∙cm2, which was increased by 28% compared to the pristine detector with a P3HT:PC71BM active layer.

Sacrificial Agent Gone Rogue: Electron-Acceptor-Induced Degradation of CsPbBr3 Photocathodes

Lead halide perovskites (LHPs) have emerged as perspective materials for light harvesting, due to their tunable band gap and optoelectronic properties. Photocatalytic and photoelectrochemical (PEC) studies, employing LHP/liquid junctions, are evolving, where sacrificial reagents are often used. In this study, we found that a frequently applied electron scavenger (TCNQ) has dual roles: while it leads to rapid electron transfer from the electrode to TCNQ, enhancing the PEC performance, it also accelerates the decomposition of the CsPbBr₃ photoelectrode. The instability of the films is caused by the TCNQ-mediated halide exchange between the dichloromethane solvent and the LHP film, during PEC operation. Charge transfer and halide exchange pathways were proposed on the basis of in situ spectroelectrochemical and ex situ surface characterization methods, also providing guidance on planning PEC experiments with such systems.

Emission wavelength control of CsPb(Br1−xClx)3 nanocrystals for blue light-emitting diode applications

A facile synthetic method of CsPb(Br_1−xCl_x)₃ halide perovskite nanocrystals, which emit light with the wavelengths ranging from green to blue based on an anion exchanging reaction using a halide exchange additive was reported.

Fast, tunable and reversible anion-exchange in CsPbBr3 perovskite nanocrystals with hydrohalic acids

Anion-exchange with metal chloride salts in CsPbBr₃ perovskite nanocrystals.

Ligand-Mediated Release of Halides for Color Tuning of Perovskite Nanocrystals with Enhanced Stability

The rich chemistry of metal halide perovskites has enabled various methods of band structure control and surface passivation. Here we report a highly facile and efficient post-treatment approach for precise color tuning of cesium lead halide perovskite nanocrystals (NCs) with enhanced stability. By utilizing a special multifunctional organic ligand, triphenyl(9-phenyl-9H-carbazol-3-yl)phosphonium bromide (TPP-Carz), carbon-halide bond cleavage can be achieved to release halide ions from halogenated solvents in a controlled manner for color tuning of perovskite NCs via ion exchange. Besides controlled release of halide ions for anion exchange, TPP-Carz can effectively passivate the surfaces of perovskite NCs simultaneously. As a result, perovskite NCs prepared by this post-treatment method with tunable colors over the entire visible spectrum have shown significantly improved luminescence and stability in comparison to the ones prepared using reactive anion precursors without surface passivation by TPP-Carz.