Perovskite Quantum Dots Films Research Articles

Inhibited Degradation of Organic–Inorganic Perovskite-Based Quantum Dot Films via Rapid Annealing Temperatures

General hot-plate heating is used to form a crystal structure of films; however, how to achieve a homogeneous and regulated crystal formation will be a crucial challenge in the future. In this study, based on perovskite-series materials, organic methylamine lead trioxide (MAPbI3) films doped with inorganic lead iodide (CsPbI3) quantum dots (QDs) are treated using the rapid thermal annealing (RTA) process in argon gas to break the crystallization barrier. These RTA-treated perovskite quantum dot (PQD) films at various temperatures of 100–160 °C are detected using X-ray diffraction, X-ray spectroscopy, and absorbance measurements to investigate their structural and optical properties as well as their binding states. The experimental results demonstrate that the PQD film annealed at 120 °C has optimized characteristics, revealing better crystallinity and the lowest content of oxygen atoms (31.4%) and C-O-C bonding (20.1%). A too-high RTA temperature, more than 140 °C, causes severe degradation with the existence of PbI2. A proper RTA process, an alternative to normal heating and annealing, can effectively inhibit the occurrence of degradation and even usefully improve the performance of PQD films.

Substrate and Excitation Intensity Dependence of Saturable Absorption in Perovskite Quantum Dot Films.

Saturable absorption in perovskite quantum dot (PQD) films, leading to saturation in photoluminescence (PL), is reported. PL of drop-casting films was used to probe how excitation intensity and host-substrate influence the growth of PL intensity. The PQD films were deposited on single-crystal GaAs, InP, Si wafers and glass. Saturable absorption was confirmed through PL saturation in all films, with different excitation intensity thresholds, suggesting strong substrate-dependent optical properties, resulting from absorption nonlinearities in the system. The observations extend our former studies (Appl. Phys. Lett., 2021, 119, 19, 192103), wherein we pointed out that the PL saturation in QDs can be used to create all-optical switches in combination with a bulk semiconductor host.

Hybrid Interfacial Engineering: An Enabling Strategy for Highly Sensitive and Stable Perovskite Quantum Dots/Organic Heterojunction Phototransistors

All-inorganic lead halide perovskite quantum dots (PQD) have attracted tremendous research interest in the field of phototransistors due to their excellent optoelectronic properties. However, the inefficient charge transport/extraction and high trap-state density of the assembled PQD films seriously limit the photoresponsivity of PQD-based phototransistors. Herein, we demonstrate that these limits can be overcome by adopting a novel device architecture composed of a polar-polymer capping layer on a PQD/organic semiconductor (OSC) heterojunction. The polar polymer film plays the role of both electron trapping and encapsulation, whereas OSC provides the fast transport tracks for charges and PQD serves as the photoactive materials. Owing to the balanced dynamic processes of photogenerated charges, highly sensitive photodetection is achieved, as demonstrated by the peak photosensitivity of 1.5 × 104, a photoresponsivity of 2.1 × 104 A/W, a detectivity of 1 × 1015 Jones, and a high gain of 6.4 × 104 under weak incident light of 3 μW/cm2. Additionally, the phototransistors exhibit superior stability and reproducibility with negligible changes in the output current both in darkness and under illumination after storing for 4 months. The results demonstrate the promising potentials of the polar polymer/PQD/OSC heterojunction for high-performance photodetectors, and the mechanism and strategy described here can be applied to other kinds of quantum dots-based optoelectronic devices.

High‐Efficiency Perovskite Quantum Dot Photovoltaic with Homogeneous Structure and Energy Landscape

AbstractThe energy disorder originating from quantum dot (QD) size and relevant solid film inhomogeneity is detrimental to the charge transport and efficiency of QD based solar cells. The emergence of halide perovskite QDs (PQDs) have attracted great attention as promising absorbers in QD photovoltaics. However, it is currently difficult in preparing structural uniform PQD film with homogenous energetic landscape, which is essential for highly reproducible and efficient solar cells. Herein, assisted by a bidentate ligand 2,5‐thiophenedicarboxylic acid, a facile solution phase anchoring (SPA) strategy is first reported for design and preparation of all‐inorganic CsPbI3 PQD film with reduced structure and energy disorder. The SPA can enhance PQD dispersion as well as dot‐to‐dot interaction, which is beneficial for fabricating high‐quality PQD arrays and photovoltaic devices. The engineered CsPbI3 PQD solar cell exhibits enhanced reproducibility, and higher open–circuit voltage together with a champion efficiency of 16.14%, which is among the highest report to date. These results are believed to provide design principle of uniform PQDs for high‐performance optoelectronic application.

Synergetic effect of ligand removal, reparation, and surface encapsulation of CsPbBr3 quantum dots with improved brightness and stability

Colloidal CsPbBr3 perovskite quantum dots (PQDs) are promising optoelectronic materials for use in solution-processed photoelectric devices. However, fabricating PQD thin films with high efficiency and good stability is still challenging. In this study, we investigate the synergetic effects of ligand removal using MeOAc washing, defect repair using cesium acetate (CsAc), and surface encapsulation using hexamethyldisilazane (HMDS) on the photoluminescence (PL) intensity and ambient stability of PQD thin films. The PL intensity is significantly improved by ligand removal and defect repair, and ambient stability is governed primarily by the SiO passivation process. However, the synergetic effect of these post-treatments is also important; the highest PL intensity and the best ambient stability are observed for the sample treated by all three post treatments in the proper order. The PL intensity is enhanced by a factor of up to 3.4, and the ambient instability is reduced by approximately 40 % compared with that of the untreated sample. Defect repair using CsAc is achievable only after the ligand is removed. Thus, these results provide essential information and an approach for post-treatments to obtain PQD films with high efficiency and robust stability.

Surface Versus Bulk State Transitions in Inkjet-Printed All-Inorganic Perovskite Quantum Dot Films.

The anion exchange of the halides, Br and I, is demonstrated through the direct mixing of two pure perovskite quantum dot solutions, CsPbBr3 and CsPbI3, and is shown to be both facile and result in a completely alloyed single phase mixed halide perovskite. Anion exchange is also observed in an interlayer printing method utilizing the pure, unalloyed perovskite solutions and a commercial inkjet printer. The halide exchange was confirmed by optical absorption spectroscopy, photoluminescent spectroscopy, X-ray diffraction, and X-ray photoemission spectroscopy characterization and indicates that alloying is thermodynamically favorable, while the formation of a clustered alloy is not favored. Additionally, a surface-to-bulk photoemission core level transition is observed for the Cs 4d photoemission feature, which indicates that the electronic structure of the surface is different from the bulk. Time resolved photoluminescence spectroscopy indicates the presence of multiple excitonic decay features, which is argued to originate from states residing at surface and bulk environments.

Energy Transfer between Size-Controlled CsPbI3 Quantum Dots for Light-Emitting Diode Application.

Perovskite quantum dots (PQDs) are applicable in light-emitting diodes (LEDs) owing to their color tunability, high color purity, and excellent photoluminescence quantum yield (PLQY) in the solution state. However, a PQD film obtained through nonradiative recombination by concentration quenching and the formation of surface defects exhibited a low PLQY. In this study, we focused on the energy transfer between PQDs with different energy gaps (Eg) to reduce nonradiative recombination in the film state and consequently achieve high device performance. We prepared size-controlled PQDs measuring 10.7 nm (large-size QD; LQD) and 7.9 nm (small-size QD; SQD) with different Eg values and observed a spectral overlap between SQD emission and LQD absorption. To investigate the Förster resonance energy transfer (FRET) from SQDs to LQDs, we prepared SQD-LQD mixed QDs (MQDs). The MQD film enhanced LQD emission and exhibited a higher PLQY (52%) with a longer PL decay time (7.4 ns) than those exhibited by the neat LQD film (38% and 6.2 ns). This energy transfer was determined to be FRET by photoluminescence excitation and PL decay times. Moreover, the external quantum efficiency of an MQD-based LED increased to 15%, indicating that the FRET process can enhance the PLQY of the film and LED efficiency.

Aggregation Control, Surface Passivation, and Optimization of Device Structure toward Near-Infrared Perovskite Quantum-Dot Light-Emitting Diodes with an EQE up to 15.4.

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI3 QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI3 QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λmax at 772nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54mA cm-2 (2.6V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.

Positive Effects of a Perovskite Film on the Radioluminescence Properties of a ZnO:Ga Crystal Scintillator.

To improve the radioluminescence (RL) performance of ZnO:Ga (GZO) crystal scintillators and overcome the challenge of their self-absorption, we proposed a two-layer composite scintillator consisting of a GZO wafer and a 70 nm lead halide perovskite film(CsPbBr3, CH3NH3PbBr3). The effects of the perovskite film on the RL properties were studied. The results showed that the perovskite quantum dot film substantially changed the RL spectrum of GZO and prevented self-absorption. The RL of the samples were enhanced by 66% to 151% through the photoluminescence (PL) of the perovskite film, while the energy-resolving power and spatial-resolving power were maintained at the same level as that of GZO image converters. The present experiments and discussions confirmed that the perovskite film improved the RL, and this study suggests a new wavelength regulation method among scintillators, converters, and back-end optical devices. The applications of perovskites in the field of radiation detection and imaging have been extended.

Ionic Liquids Modulating CsPbI3 Colloidal Quantum Dots Enable Improved Mobility for High-Performance Solar Cells.

Colloidal all-inorganic CsPbI3 perovskite quantum dots (PQDs) have shown tremendous potential in photovoltaic applications in recent years due to their outstanding optoelectronic properties that general metal halide perovskites offer, along with the added advantages that originates from size reduction and the quantum confinement effect. However, the issue of low carrier mobility in PQD films caused by insulating organic ligands capped on the PQD surface still remains to be addressed while aiming for high-efficiency PQD solar cells. Herein, we propose a novel strategy that takes benefits of ionic liquids, which can offer the high polarity and the electron donating ability to boost the mobility of PQD films in photovoltaic devices. Specifically, 1-propyl-3-methylimidazolium iodide to modulate the colloidal CsPbI3 PQD surface and couple QDs is demonstrated for the first time. The lone pair electrons on the nitrogen of the imidazole ring within the ionic liquid binds to the empty nonbonding surface orbitals of CsPbI3 PQDs while the long-chain insulating ligands are replaced, which enables not only efficient charge transport but also reduced defect density in the assembled PQD solid films. The resulting CsPbI3 PQD solar cell shows a significant increase in efficiency with suppressed hysteresis, indicating the impressive potential of this strategy for developing highly efficient PQD solar cells.

Luminescence Mechanism of Perovskite Quantum Dot Films Pumped by Electron Beam

Luminescence Mechanism of Perovskite Quantum Dot Films Pumped by Electron Beam

Ultrahigh-Performance Optoelectronic Skin Based on Intrinsically Stretchable Perovskite-Polymer Heterojunction Transistors.

The optoelectronic skin is acknowledged as the world's current cutting-edge technology in the fields of wearable healthcare monitoring, soft robotics, artificial retinas, and so on. However, the difficulty in preparing stretchable photosensitive polymers and the high-crystallization nature of most reported photosensitive materials (such as perovskites) severely restrict the development of skin-like optoelectronic devices. Herein, a surface energy-induced self-assembly methodology is proposed to form easily transferrable and flexible perovskite quantum dot (PQD) films with a worm-like morphology. Furthermore, intrinsically stretchable phototransistors (ISTPTs) are fabricated based on a stretchable photosensitive layer heterojunction consisting of worm-like PQD films and hybrid polymer semiconductors. The obtained ISTPTs display highly sensitive response to high-energy photons of X-ray (with a detection limit of 79 nGy s-1 , that is 560 times lower than commercial medical chest X-ray diagnosis) and ultraviolet (with photosensitivity of 5 × 106 and detectable light intensity of 50 nW cm-2 among the highest performance of reported photodetectors). In addition, these ISTPTs demonstrate desirable e-skin characteristics with high strain tolerance, high sensing specificity, high optical transparency, and good skin conformability. The surface energy-induced self-assembly methodology for the preparation of ISTPTs is a critical demonstration to enable low-cost and high-performance optoelectronic skins.

Drop-casting CsPbBr3 perovskite quantum dots as down-shifting layer enhancing the ultraviolet response of silicon avalanche photodiode

Since the absorption zone of ultraviolet (UV) photons with high energy is limited to a few tens of nm on the surface, the high defect density caused by the processes, such as ion implantation, leads to a weak response of the silicon avalanche photodiode (APD) in the ultraviolet band. In this work, the integration of the inorganic perovskite quantum dots (QDs) film by drop-casting as the down-shifting layer is reported for enhancing the UV response of Si APD. The light generated current increases 100% under the 365 nm light emitting diode. The response of the Si APD is improved in the entire ultraviolet band. In particular, the responsivity of APD is increased by 78% at 340 nm with an exceedingly EQE of 92%. In summary, the perovskite QDs film as a down-shifting layer provides an effective and low-cost method to improve the UV response of Si APD.

Ultra-low EQE roll-off and marvelous efficiency perovskite quantum-dots light-emitting-diodes achieved by ligand passivation

Recently, perovskite quantum dots (PQDs) were employed as promising emitters in light-emitting diode devices (LEDs) mainly owing to their marvelous photoelectronics properties. However, these perovskite QLEDs suffered from the inefficient performance, especially their serious efficiency roll-off probably due to the exciton recombination dynamic in the interface of PQDs films and charge imbalance resulting from low electrical transportation. Herein, sodium dodecyl sulfate (SDS) was effectively introduced to synthesize PQDs with many excellent properties and eventually suppressed the efficiency roll-off of QLEDs. SDS-based PQDs films exhibited obviously enhanced radiative recombination, reduced trap density, and increased carrier mobility, especially the transportation of electrons. Therefore, the charge carrier was balanced at high current density together with the remarkably suppressed efficiency roll-off. QLEDs fabricated by SDS-capped PQDs exhibited significantly improved maximum brightness of 193,810 cd/m2, and achieve the external quantum efficiency of 10.13%. More importantly, the EQE roll-off of QLED optimized in the thickness of emitting layer was only 1.5% at the current density of 200 mA/cm2, representing a prominent achievement of our strategy.

Enhancement of Light Amplification of CsPbBr3 Perovskite Quantum Dot Films via Surface Encapsulation by PMMA Polymer.

Photonic devices based on perovskite materials are considered promising alternatives for a wide range of these devices in the future because of their broad bandgaps and ability to contribute to light amplification. The current study investigates the possibility of improving the light amplification characteristics of CsPbBr3 perovskite quantum dot (PQD) films using the surface encapsulation technique. To further amplify emission within a perovskite layer, CsPbBr3 PQD films were sandwiched between two transparent layers of poly(methyl methacrylate) (PMMA) to create a highly flexible PMMA/PQD/PMMA waveguide film configuration. The prepared perovskite film, primed with a polymer layer coating, shows a marked improvement in both emission efficiency and amplified spontaneous emission (ASE)/laser threshold compared with bare perovskite films on glass substrates. Additionally, significantly improved photoluminescence (PL) and long decay lifetime were observed. Consequently, under pulse pumping in a picosecond duration, ASE with a reduction in ASE threshold of ~1.2 and 1.4 times the optical pumping threshold was observed for PQDs of films whose upper face was encapsulated and embedded within a cavity comprising two PMMA reflectors, respectively. Moreover, the exposure stability under laser pumping was greatly improved after adding the polymer coating to the top face of the perovskite film. Finally, this process improved the emission and PL in addition to enhancements in exposure stability. These results were ascribed in part to the passivation of defects in the perovskite top surface, accounting for the higher PL intensity, the slower PL relaxation, and for about 14 % of the ASE threshold decrease.

28.3: Stabilization of photoluminescence perovskite nanocrystals via atomic layer deposition and the process influences

We report the effects of low temperature atomic layer deposition (ALD) environment treatment on the photoluminescence properties and stability of perovskite quantum dot films. Compared with conventional chemical centrifugation, the loss of photoluminscence can be reduced by physical pressure and temperature control. The photoluminescence properties and long‐term stability of the films can be improved by vacuum heating and washing with weak polar solvents to reduce the content of organic matter on the surface. It also suggests that the colloidal environment of organic solvent and the air environment of device structure should be separated to explain the mechanism of stability during the preparation of QDs films by solution method. Besides, it provides a vision for further interpretation of the luminescence properties of quantum dot thin film materials by using ALD to accurately control the atmosphere, temperature and pressure.

53.3: Investigation of AlGaN‐based Deep‐UV Micro‐LED as Highly Efficient Excitation Source for Green Perovskite Quantum Dots Display

Displays based on inorganic micro light‐emitting diodes (Micro‐LED) are highly anticipated for the next‐generation display technologies. Deep‐UV Micro‐LED as the excitation source for green perovskite quantum dots display with high efficiency is demonstrated in this paper. Deep‐UV Micro‐LEDs were fabricated in different device sizes and lighted‐up on a green perovskite quantum dot film The peak wavelength of Deep‐UV light shows a blue shift with the increasing current density. The light output intensity of a 300 × 200 — pixel Deep‐UV Micro‐LED array with each pixel size of 30×30 µm2 is shown in the distribution map.

Design of Chemically Stable Organic Perovskite Quantum Dots for Micropatterned Light-Emitting Diodes through Kinetic Control of a Cross-Linkable Ligand System.

Perovskite quantum dot (QD) light-emitting diodes (PeLEDs) are ideal for next-generation display applications because of their excellent color purity, high efficiency, and cost-effective fabrication. However, developing a technology for high-resolution multicolor patterning of perovskite QDs remains challenging, owing to the chemical instability of these materials. To overcome these issues, in this work, the generation of surface defects is prevented by controlling the ligand-binding kinetics using a stable ligand system (Stable LS). The crystalline reconstruction of perovskite QDs after addition of the Stable LS results in an ≈18% increase in their photoluminescence quantum yield in solution and it also improves the ambient stability of the perovskite QD solution. Moreover, the perovskite QDs with Stable LS can undergo cross-linking under UV irradiation. The tightly bridged perovskite QDs effectively prevent moisture-assisted ligand dissociation in film state due to the increased hydrophobicity and restricted movement of the cross-linked surface ligands. Thus, the cross-linked perovskite QD film shows improved chemical/environmental stability without substantial deterioration in optoelectrical properties. As a result, a white electroluminescent device with high resolution (≈1 μm) is successfully fabricated by inkjet printing using green and red perovskite QDs.

62‐9: Invited Paper: Hybrid Composite Films with Perovskite Quantum Dots and Red Phosphors for LCD Display Backlights

Perovskite quantum dots films (PQDF) are emerging as low‐cost alternatives to improve the color gamut of liquid crystal display (LCD) backlights due to their narrow half peak width. In this paper, hybrid composite films with green perovskite quantum dots (PQDs) and red rare earth phosphors were combined in a dual layer film for LCD backlight display applications. By combining the in‐situ fabricated green emissive PQDF with KSF phosphor or red nitride phosphor (NP), we prepared hybrid composite films of green PQDF and red phosphors with high brightness and wide color gamut. The color gamut of PQDs‐KSF is 83.1% of Rec. 2020 due to the narrow full‐width‐at‐half‐maximum of PQDs and KSF phosphors. These composite films have great potential in the application of LCD backlights.

61‐3: Investigation of AlGaN‐Based Deep‐UV MicroLED as Highly Efficient Excitation Source for Green Perovskite Quantum‐Dot Display

Displays based on inorganic micro light‐emitting diodes (MicroLED) are highly anticipated for the next‐generation display technologies. Deep‐UV Micro‐LED as the excitation source for green perovskite quantum dots display with high efficiency is demonstrated in this paper. Deep‐UV Micro‐LEDs were fabricated in different device sizes and lighted‐up on a green perovskite quantum dot film. The peak wavelength of Deep‐UV light shows a blue shift with the increasing current density. The light output intensity of a 300 × 200 ‐ pixel Deep‐UV Micro‐LED array with each pixel. size of 30×30 µm2 is shown in the distribution map.