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13 pages, 2691 KiB

Open AccessArticle

Hybrid Amino Acid Ligand-Regulated Excited Dynamics of Highly Luminescent Perovskite Quantum Dots for Bright White Light-Emitting Diodes

by Baoye Hu, Weiqiang Zhang and Ya Chu

Nanomaterials 2024, 14(15), 1266; https://doi.org/10.3390/nano14151266 - 29 Jul 2024

Viewed by 880

Abstract

Organic–inorganic hybrid perovskite quantum dots (QDs) have garnered significant research interest owing to their unique structure and optoelectronic properties. However, their poor optical performance in ambient air remains a significant limitation, hindering their advancement and practical applications. Herein, three amino acids (valine, threonine [...] Read more.

Organic–inorganic hybrid perovskite quantum dots (QDs) have garnered significant research interest owing to their unique structure and optoelectronic properties. However, their poor optical performance in ambient air remains a significant limitation, hindering their advancement and practical applications. Herein, three amino acids (valine, threonine and cysteine) were chosen as surface ligands to successfully prepare highly luminescent CH₃NH₃PbBr₃ (MAPbBr₃) QDs. The morphology and XRD results suggest that the inclusion of the amino acid ligands enhances the octahedral structure of the QD solutions. Moreover, the observed blue-shifted phenomenon in the photoluminescence (PL) aligns closely with the blue-shifted phenomenon observed in the ultraviolet–visible (UV-Vis) absorption spectra, attributed to the quantum confinement effect. The time-resolved spectra indicated that the introduction of the amino acid ligands successfully suppressed non-radiative recombination, consequently extending the fluorescence lifetime of the MAPbBr₃ QDs. The photoluminescence quantum yields (PLQYs) of the amino acid-treated MAPbBr₃ QDs are increased by 94.8%. The color rendering index (CRI) of the produced white light-emitting diode (WLED) is 85.3, with a correlated color temperature (CCT) of 5453 K. Our study presents a novel approach to enhancing the performance of perovskite QDs by employing specially designed surface ligands for surface passivation. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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13 pages, 653 KiB

Open AccessArticle

GaAs Cone-Shell Quantum Dots in a Lateral Electric Field: Exciton Stark-Shift, Lifetime, and Fine-Structure Splitting

by Ahmed Alshaikh, Robert H. Blick and Christian Heyn

Nanomaterials 2024, 14(14), 1174; https://doi.org/10.3390/nano14141174 - 10 Jul 2024

Viewed by 647

Abstract

Strain-free GaAs cone-shell quantum dots have a unique shape, which allows a wide tunability of the charge-carrier probability densities by external electric and magnetic fields. Here, the influence of a lateral electric field on the optical emission is studied experimentally using simulations. The [...] Read more.

Strain-free GaAs cone-shell quantum dots have a unique shape, which allows a wide tunability of the charge-carrier probability densities by external electric and magnetic fields. Here, the influence of a lateral electric field on the optical emission is studied experimentally using simulations. The simulations predict that the electron and hole form a lateral dipole when subjected to a lateral electric field. To evaluate this prediction experimentally, we integrate the dots in a lateral gate geometry and measure the Stark-shift of the exciton energy, the exciton intensity, the radiative lifetime, and the fine-structure splitting (FSS) using single-dot photoluminescence spectroscopy. The respective gate voltage dependencies show nontrivial trends with three pronounced regimes. We assume that the respective dominant processes are charge-carrier deformation at a low gate voltage U, a vertical charge-carrier shift at medium U, and a lateral charge-carrier polarization at high U. The lateral polarization forms a dipole, which can either enhance or compensate the intrinsic FSS induced by the QD shape anisotropy, dependent on the in-plane orientation of the electric field. Furthermore, the data show that the biexciton peak can be suppressed by a lateral gate voltage, and we assume the presence of an additional vertical electric field induced by surface charges. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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11 pages, 2202 KiB

Open AccessArticle

Study of Laser-Induced Multi-Exciton Generation and Dynamics by Multi-Photon Absorption in CdSe Quantum Dots

by Peng Zhang, Yimeng Wang, Xueqiong Su, Qiwen Zhang and Mingyu Sun

Nanomaterials 2024, 14(7), 558; https://doi.org/10.3390/nano14070558 - 22 Mar 2024

Viewed by 1044

Abstract

Multi-exciton generation by multi-photon absorption under low-energy photons can be thought a reasonable method to reduce the risk of optical damage, especially in photoelectric quantum dot (QD) devices. The lifetime of the multi-exciton state plays a key role in the utilization of photon-induced [...] Read more.

Multi-exciton generation by multi-photon absorption under low-energy photons can be thought a reasonable method to reduce the risk of optical damage, especially in photoelectric quantum dot (QD) devices. The lifetime of the multi-exciton state plays a key role in the utilization of photon-induced carriers, which depends on the dynamics of the exciton generation process in materials. In this paper, the exciton generation dynamics of the photon absorption under low-frequency light in CdSe QDs are successfully detected and studied by the temporal resolution transient absorption (TA) spectroscopy method. Since the cooling time of hot excitons extends while the rate of auger recombination is accelerated when incident energy is increased, the filling time of defect states is irregular, and exciton generation experiences a transition from single-photon absorption to multi-photon absorption. This result shows how to change the excitation. Optical parameters can prolong the lifetime of excitons, thus fully extracting excitons and improving the photoelectric conversion efficiency of QD optoelectronic devices, which provides theoretical and experimental support for the development of QD optoelectronic devices. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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11 pages, 2803 KiB

Open AccessArticle

In-Depth Insight into the Effect of Hydrophilic-Hydrophobic Group Designing in Amidinium Salts for Perovskite Precursor Solution on Their Photovoltaic Performance

by Guohua Wu, Hua Li, Shuai Chen, Shengzhong (Frank) Liu, Yaohong Zhang and Dapeng Wang

Nanomaterials 2022, 12(21), 3881; https://doi.org/10.3390/nano12213881 - 3 Nov 2022

Viewed by 1870

Abstract

Amidinium salts have been utilized in perovskite precursor solutions as additives to improve the quality of perovskite films. The design of hydrophilic or hydrophobic groups in amidinium salts is of great importance to photovoltaic device performance and stability in particular. Here we report [...] Read more.

Amidinium salts have been utilized in perovskite precursor solutions as additives to improve the quality of perovskite films. The design of hydrophilic or hydrophobic groups in amidinium salts is of great importance to photovoltaic device performance and stability in particular. Here we report a contrast study of a guanidinium iodide (GUI) additive with a hydrophilic NH₂ group, and a N,1–diiodoformamidine (DIFA) additive with a hydrophobic C–I group, to investigate the group effect. The addition of GUI or DIFA was beneficial to achieve high quality perovskite film and superior photovoltaic device performance. Compared with GUI, the addition of the DIFA in a perovskite precursor solution enhanced the crystal quality, reduced the defect density, and protected the water penetration into perovskite film. The perovskite solar cell (PSC) devices showed the best power conversion efficiency (PCE) of 21.19% for those modified with DIFA, as compared to 18.85% for the control, and 20.85% for those modified with GUI. In benefit to the hydrophobic C–I group, the DIFA–modified perovskite films and PSC exhibited the best light stability, thermal stability, and humidity stability in comparison to the control films and GUI–modified films. Overall, the introduction of a hydrophobic group in the amidinium salts additive was demonstrated to be an efficient approach to achieve high quality and stable perovskite film and PSC devices. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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10 pages, 2971 KiB

Open AccessArticle

Optimizing the Synthetic Conditions of “Green” Colloidal AgBiS₂ Nanocrystals Using a Low-Cost Sulfur Source

by Qiao Li, Xiaosong Zheng, Xiaoyu Shen, Shuai Ding, Hongjian Feng, Guohua Wu and Yaohong Zhang

Nanomaterials 2022, 12(21), 3742; https://doi.org/10.3390/nano12213742 - 25 Oct 2022

Cited by 8 | Viewed by 2311

Abstract

Colloidal AgBiS₂ nanocrystals (NCs) have attracted increasing attention as a near–infrared absorbent materials with non–toxic elements and a high absorption coefficient. In recent years, colloidal AgBiS₂ NCs have typically been synthesized via the hot injection method using hexamethyldisilathiane (TMS) as the [...] Read more.

Colloidal AgBiS₂ nanocrystals (NCs) have attracted increasing attention as a near–infrared absorbent materials with non–toxic elements and a high absorption coefficient. In recent years, colloidal AgBiS₂ NCs have typically been synthesized via the hot injection method using hexamethyldisilathiane (TMS) as the sulfur source. However, the cost of TMS is one of the biggest obstacles to large–scale synthesis of colloidal AgBiS₂ NCs. Herein, we synthesized colloidal AgBiS₂ NCs using oleylamine@sulfur (OLA–S) solution as the sulfur source instead of TMS and optimized the synthesis conditions of colloidal AgBiS₂ NCs. By controlling the reaction injection temperature and the dosage of OLA–S, colloidal AgBiS₂ NCs with adjustable size can be synthesized. Compared with TMS–based colloidal AgBiS₂ NCs, the colloidal AgBiS₂ NCs based on OLA–S has good crystallinity and fewer defects. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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10 pages, 4229 KiB

Open AccessArticle

Quantum Mechanical Analysis Based on Perturbation Theory of CdSe/ZnS Quantum-Dot Light-Emission Properties

by Honyeon Lee and Dongjin Kim

Nanomaterials 2022, 12(20), 3590; https://doi.org/10.3390/nano12203590 - 13 Oct 2022

Cited by 4 | Viewed by 1339

Abstract

A simulation of quantum dot (QD) energy levels was designed to reproduce a quantum mechanical analytic method based on perturbation theory. A Schrödinger equation describing an electron–hole pair in a QD was solved, in consideration of the heterogeneity of the material parameters of [...] Read more.

A simulation of quantum dot (QD) energy levels was designed to reproduce a quantum mechanical analytic method based on perturbation theory. A Schrödinger equation describing an electron–hole pair in a QD was solved, in consideration of the heterogeneity of the material parameters of the core and shell. The equation was solved numerically using single-particle basis sets to obtain the eigenstates and energies. This approach reproduced an analytic solution based on perturbation theory, while the calculation was performed using a numerical method. Owing to the effectiveness of the method, QD behavior according to the core diameter and external electric field intensity could be investigated reliably and easily. A 9.2 nm diameter CdSe/ZnS QD with a 4.2 nm diameter core and 2.5 nm thick shell emitted a 530 nm green light, according to an analysis of the effects of core diameter on energy levels. A 4 nm redshift at

5.4 \times 10^{5}

V/cm electric field intensity was found while investigating the effects of external electric field on energy levels. These values agree well with previously reported experimental results. In addition to the energy levels and light emission wavelengths, the spatial distributions of wavefunctions were obtained. This analysis method is widely applicable for studying QD characteristics with varying structure and material compositions and should aid the development of high-performance QD technologies. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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13 pages, 684 KiB

Open AccessFeature PaperArticle

Optical Absorption on Electron Quantum-Confined States of Perovskite Quantum Dots

by Serhii I. Pokutnii and Andrzej Radosz

Nanomaterials 2022, 12(17), 2973; https://doi.org/10.3390/nano12172973 - 28 Aug 2022

Viewed by 1396

Abstract

In the framework of the dipole approximation, it is shown that in the perovskites quantum dots (QDs)

{FAPbBr}_{3}

and {en}

{FAPbBr}_{3}

interacting with low-intensity light, the oscillator strengths of transitions, as well as the dipole moments allowing transitions [...] Read more.

In the framework of the dipole approximation, it is shown that in the perovskites quantum dots (QDs)

{FAPbBr}_{3}

and {en}

{FAPbBr}_{3}

interacting with low-intensity light, the oscillator strengths of transitions, as well as the dipole moments allowing transitions between one-particle electron quantum-confined states, attain values considerably (by two orders of magnitude) exceeding the typical values of the corresponding quantities in semiconductors. It has been established that the maximum values of the cross-section optical absorption of perovskite QDs are reached at the resonant frequencies of electron transitions. This makes it possible to use such nanosystems as of strong absorption nanomaterials in a wide range of infrared waves. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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Review

Jump to: Research

18 pages, 3907 KiB

Open AccessReview

All–Inorganic Perovskite Quantum Dot–Based Blue Light–Emitting Diodes: Recent Advances and Strategies

by Yuyu Hu, Shijie Cao, Peng Qiu, Meina Yu and Huiyun Wei

Nanomaterials 2022, 12(24), 4372; https://doi.org/10.3390/nano12244372 - 8 Dec 2022

Cited by 5 | Viewed by 2693

Abstract

Light–emitting diodes (LEDs) based on all–inorganic lead halide perovskite quantum dots (PQDs) have undergone rapid development especially in the past five years, and external quantum efficiencies (EQEs) of the corresponding green– and red–emitting devices have exceeded 23%. However, the blue–emitting devices are facing [...] Read more.

Light–emitting diodes (LEDs) based on all–inorganic lead halide perovskite quantum dots (PQDs) have undergone rapid development especially in the past five years, and external quantum efficiencies (EQEs) of the corresponding green– and red–emitting devices have exceeded 23%. However, the blue–emitting devices are facing greater challenges than their counterparts, and their poor luminous efficiency has hindered the display application of PQD–based LEDs (PeQLEDs). This review focuses on the key challenges of blue–emitting PeQLEDs including low EQEs, short operating lifetime, and spectral instability, and discusses the essential mechanism by referring to the latest research. We then systematically summarize the development of preparation methods of blue emission PQDs, as well as the current strategies on alleviating the poor device performance involved in composition engineering, ligand engineering, surface/interface engineering, and device structural engineering. Ultimately, suggestions and outlooks are proposed around the major challenges and future research direction of blue PeQLEDs. Full article

(This article belongs to the Special Issue Quantum Dot Materials and Optoelectronic Devices)

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