Great Potential For Optoelectronic Applications Research Articles

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots.

InP quantum dots (QDs) have attracted much attention owing to their nontoxic properties and shown great potential in optoelectronic applications. Due to the surface defects and lattice mismatch, the interfacial structure of InP/ZnS QDs plays a significant role in their performance. Herein, the formation of In-S and Sx -In-P1-x interlayers through anion exchange at the shell-growth stage is revealed. More importantly, it is proposed that the composition of interface is dependent on the synergistic effect of halogen ions and shelling temperature. High shelling temperature contributes to the optical performance improvement resulting from the formation of interlayers, besides the thicker ZnS shell. Moreover, the effect relates to the halogen ions where I- presents more obvious enhancement than Br- and Cl- , owing to their different ability to coordinate with In dangling bonds, which are inclined to form In-S and Sx -In-P1-x bonds. Further, the anion exchange under I- -rich environment causes a blue-shift of emission wavelength with shelling temperature increasing, unobserved in a Cl- - or Br- -rich environment. It contributes to the preparation of highly efficient blue emissive InP/ZnS QDs with emission wavelength of 473nm, photoluminescence quantum yield of ≈50% and full width at half maximum of 47nm.

Solution-Processed CsPbBr3 Quantum Dots/Organic Semiconductor Planar Heterojunctions for High-Performance Photodetectors.

Planar heterojunctions (PHJs) are fundamental building blocks for construction of semiconductor devices. However, fabricating PHJs with solution‐processable semiconductors such as organic semiconductors (OSCs) is a challenge. Herein, utilizing the orthogonal solubility and good wettability between CsPbBr3 perovskite quantum dots (PQDs) and OSCs, fabrication of solution‐processed PQD/OSC PHJs are reported. The phototransistors based on bilayer PQD/PDVT‐10 PHJs show responsivity up to 1.64 × 104 A W−1, specific detectivity of 3.17 × 1012 Jones, and photosensitivity of 5.33 × 106 when illuminated by 450 nm light. Such high photodetection performance is attributed to efficient charge dissociation and transport, as well as the photogating effect in the PHJs. Furthermore, the tri‐layer PDVT‐10/PQD/Y6 PHJs are used to construct photodiodes working in self‐powered mode, which exhibit broad range photoresponse from ultraviolet to near‐infrared, with responsivity approaching 10−1 A W−1 and detectivity over 106 Jones. These results present a convenient and scalable production processes for solution‐processed PHJs and show their great potential for optoelectronic applications.

Methanol-induced luminescence vapochromism based on a Sb3+-doped organic indium halide hybrid

Ion doping has been demonstrated as a practical approach to achieving highly efficient luminescence in both inorganic phosphors and organic-inorganic hybrids. The as-formed doping species show great potential in optoelectronic applications due to their high photoluminescence quantum yield (PLQY) and excellent stability. Herein, we report highly emissive Sb3+-doped indium halides (C6H18N2)InCl5·H2O:Sb (C6H18N22+ = N,N,N′,N′-tetramethylethane-1,2-diammonium) prepared by solution evaporation methods with an emission that peaked at 565 nm and a PLQY of 74.6%. Photophysical characterizations and density functional theory computational studies verify the broadband emission originating from a self-trapped exciton. Interestingly, a drastic red shift of the emission peak from 565 to 663 nm with yellow luminescence turning to red is observed once the (C6H18N2)InCl5·H2O:Sb hybrid is exposed to methanol vapor. Moreover, when the methanol-exposed hybrid is put in air, the emission reverts to 565 nm in several minutes. Single-crystal X-ray diffraction studies show a subsequent structure distortion upon the coordination of methanol to the Sb(III) center, which is responsible for the drastic red shift of the emission. Encouragingly, we found that (C6H18N2)InCl5·H2O:Sb exhibits a specific response to methanol vapor after screening a series of volatile organic compounds with different polarities. Besides, a negligible change of the emission intensity is observed after several cycles of uptaking and releasing methanol. The high fatigue resistance and specific solvent response of the Sb3+-doped indium halide make it a very promising methanol detector.

Crossover between Bulk and Interface Photovoltaic Mechanisms in a Ferroelectric Vertical Heterostructure

The bulk photovoltaic (BPVE) effect in crystals lacking inversion symmetry offers great potential for optoelectronic applications due to its unique properties, such as above-band-gap photovoltage and switchable photocurrent. Because of their large spontaneous polarizations, ferroelectric materials are ideal platforms for studying the BPVE. However, identifying the origin of an experimentally observed photovoltaic response is often challenging due to the entanglement between bulk and interface effects, leading to much debate in the field. This issue is particularly pronounced in vertical heterostructures, where the two effects are comparable. Here, we report crossover between bulk- and interface-dominant responses in vertical ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_{3}$ heterostructures when changing the photon energy. We show that well-above-band-gap excitation leads to a bulk photovoltaic response, but band-edge excitation requires interface band bending to separate the photocarriers. Our findings not only help to clarify contradicting reports in the literature, but also lay the foundation for a deeper understanding of the ferroelectric photovoltaic effect and its applications in various devices.

Efficiently Improved Photoluminescence in Cesium Lead Halide Perovskite Nanocrystals by Using Bis(trifluoromethane)sulfonimide.

Cesium lead halide perovskite (CsPbX3, X = Cl, Br, and I) nanocrystals (NCs) have attracted enormous attention because of their great potential for optoelectronic applications, such as light-emitting diodes (LEDs). However, the photoluminescence and surface ligands of CsPbX3 NCs have a great impact on their device applications. Herein, we report a molecular superacid of bis(trifluoromethane)sulfonimide (TFSI), which could boost the photoluminescence in the metal halide perovskite nanocrystals. In particular, the photoluminescence quantum yield (PLQY) of CsPbI3 nanocrystals could be greatly improved from 28.6% to near 100% with the superacid treatment. The improved PLQY in CsPbX3 nanocrystals is mainly contributed from the surface passivation based on the characterizations. The CsPbX3 nanocrystals were further modified with PMMA, which could greatly improve their stability while preserving high photoluminescence and good dispersion. The use of superacid combined with a polymer for improving the photoluminescence and stability in CsPbX3 provides an alternative strategy for optoelectronics.

In Situ Embedding Synthesis of CsPbBr3@Ce-MOF@SiO2 Nanocomposites for High Efficiency Light-Emitting Diodes: Suppressing Reabsorption Losses through the Waveguiding Effect.

All-inorganic perovskite quantum dots (PQDs), which possess outstanding photophysical properties, are regarded as promising materials for optoelectronic applications. However, the poor light conversion efficiency and severe stability problem hinder their widespread applications. In this work, a novel encapsulation strategy is developed through the in situ growth of CsPbX3 PQDs in presynthesized mesoporous cerium-based metal organic frameworks (Ce-MOFs) and further silane hydrolysis-encapsulation, generating stable CsPbX3@Ce-MOF@SiO2 composites with greatly enhanced light conversion efficiency. Moreover, the simulation results suggest that the pore boundary of Ce-MOFs has a strong waveguide effect on the incident PQD light, constraining PQD light inside the bodies of Ce-MOFs and suppressing reabsorption losses, thus increasing the overall light conversion efficiency of PQDs. Meanwhile, the Ce-MOF@SiO2 protective shell effectively improves the stability by blocking internally embedded PQDs from the harmful external environment. Further, the obtained white-light-emitting diode shows an ultrahigh luminous efficiency of 87.8 lm/W, which demonstrates their great potential in optoelectronic applications.

Layered transition metal chalcogenophosphate towards air-stable visible light photodetection

Two-dimensional (2D) multiple-element layered transition metal chalcogenophosphates (TMCPs) have received tremendous attention due to their excellent carrier mobility, and absorption coefficient, displaying great potential for optoelectronic applications. Here, the novel high-quality manganese nickel phosphorous sulfur (Mn0.24Ni0.76PS3) crystals are obtained by using chemical vapor transport (CVT) method. Further, thin flakes of Mn0.24Ni0.76PS3 are achieved and employed to prepare photodetectors. Impressively, the prepared photodetectors exhibit excellent photo-response in visible light region, such as on/off ratio, and response time, a responsivity up to 10.4 mA W−1 and a detectivity of 1.31 × 108 Jones, demonstrating great potential for future air-stable visible light photodetection.

Pressure-induced bandgap engineering and photoresponse enhancement of wurtzite CuInS2 nanocrystals

Wurtzite CuInS2 exhibits great potential for optoelectronic applications because of its excellent optical properties and good stability. However, exploring effective strategies to simultaneously optimize its optical and photoelectrical properties remains a challenge. In this study, the bandgap of wurtzite CuInS2 nanocrystals is successfully extended and the photocurrent is enhanced synchronously using external pressure. The bandgap of wurtzite CuInS2 increases with pressure and reaches an optimal value (1.5 eV) for photovoltaic solar energy conversion at about 5.9 GPa. Surprisingly, the photocurrent simultaneously increases nearly 3-fold and reaches the maximum value at this critical pressure. Theoretical calculation indicates that the pressure-induced bandgap extention in wurtzite CuInS2 may be attributed to an increased charge density and ionic polarization between the In-S atoms. The photocurrent preserves a relatively high photoresponse even at 8.8 GPa, but almost disappears above 10.3 GPa. The structural evolution demonstrates that CuInS2 undergoes a phase transformation from the wurtzite phase (P63mc) to the rock salt phase (Fm3̄m) at about 10.3 GPa, which resulted in a direct to indirect bandgap transition and fianlly caused a dramatic reduction in photocurrent. These results not only map a new route toward further increase in the photoelectrical performance of wurtzite CuInS2, but also advance the current research of AI-BIII-CVI2 materials.

High-resolution in situ patterning of perovskite quantum dots via femtosecond laser direct writing.

Colloidal quantum dots (QDs) have exhibited great potential for optoelectronic applications, including displays, lasers, anti-counterfeiting and information storage. However, the high-resolution patterning technique of QDs is still a challenge, while precise patterned QDs are of great value for practical applications. Here, a femtosecond laser direct writing strategy was demonstrated for the in situ fabrication of high-resolution-patterned perovskite quantum dots (PQDs) by the laser-induced Marangoni flow to aggregate and deposit the PQDs based on the opto-thermoelectric mechanism. By regulating the laser power and the exposure time, the minimum line width could reach 1.58 μm. Importantly, through the patterning of red, green and blue PQDs, the strategy exhibited the applicability in full-color PQD materials. Moreover, the deposited PQDs can preserve the original photophysical properties including photoluminescence spectra and excited state lifetime. The approach provides a strategy to fabricate high-resolution patterned PQDs in situ, which is a promising alternative in photonic applications including high-resolution displays and anti-counterfeiting.

Enhancement of Photoresponse on Narrow-Bandgap Mott Insulator α-RuCl3 via Intercalation.

Charge doping to Mott insulators is critical to realize high-temperature superconductivity, quantum spin liquid state, and Majorana fermion, which would contribute to quantum computation. Mott insulators also have a great potential for optoelectronic applications; however, they showed insufficient photoresponse in previous reports. To enhance the photoresponse of Mott insulators, charge doping is a promising strategy since it leads to effective modification of electronic structure near the Fermi level. Intercalation, which is the ion insertion into the van der Waals gap of layered materials, is an effective charge-doping method without defect generation. Herein, we showed significant enhancement of optoelectronic properties of a layered Mott insulator, α-RuCl3, through electron doping by organic cation intercalation. The electron-doping results in substantial electronic structure change, leading to the bandgap shrinkage from 1.2 eV to 0.7 eV. Due to localized excessive electrons in RuCl3, distinct density of states is generated in the valence band, leading to the optical absorption change rather than metallic transition even in substantial doping concentration. The stable near-infrared photodetector using electronic modulated RuCl3 showed 50 times higher photoresponsivity and 3 times faster response time compared to those of pristine RuCl3, which contributes to overcoming the disadvantage of a Mott insulator as a promising optoelectronic device and expanding the material libraries.

Hot Electron Tunneling in Pt/LaAlO3/SrTiO3 Heterostructures for Enhanced Photodetection.

LaAlO3/SrTiO3 (LAO/STO) heterostructures, in which a highly mobile two-dimensional electron gas (2DEG) is formed, have great potential for optoelectronic applications. However, the inherently high density of the 2DEG hinders the observation of photo-excitation effects in oxide heterostructures. Herein, a strong photoresponse of the 2DEG in a Pt/LAO/STO heterostructure is achieved by adopting a vertical tunneling configuration. The tunneling of the 2DEG through an ultrathin LAO layer is significantly enhanced by UV light irradiation, showing a maximum photoresponsivity of ∼1.11 × 107%. The strong and reversible photoresponse is attributed to the thermionic emission of photoexcited hot electrons from the oxygen-deficient STO. Notably, the oxygen vacancy defects play a critical role in enhancing the tunneling photocurrent. Our systematic study on the hysteresis behavior and the light power dependency of the tunneling current consistently support the fact that the photoexcited hot electrons from the oxygen vacancies strongly contribute to the tunneling conduction under the UV light. This work offers valuable insights into a novel photodetection mechanism based on the 2DEG as well as into developing ultrathin optoelectronic devices based on the oxide heterostructures.

Fabrication of ultra-violet photodetector with enhanced optoelectronic parameters using low-cost F-doped ZnO nanostructures

In this work, photodetectors based on undoped (ZO) and fluorine-doped ZnO (FZO) nanostructured films were fabricated on silicon substrates using the hydrothermal method. The morphological, compositional, structural changes, and UV detection properties were investigated. FESEM and TEM revealed well-arranged vertically aligned nanorod (NRs) growth on the substrate. XRD analysis revealed a hexagonal structure of the ZnO phase with a strong (002) predominance of the peak plane. XPS and EDX analyses have shown the presence of fluorine doping. F-doping increases the band gap value of the growing material from 3.26 to 3.28 eV. The photocurrent value has improved significantly from 7.37 μA to 624.37 μA at 4 V. The response speed, responsivity, detectivity, and external quantum efficiency of ZO and FZO were also investigated and comparisons were made. We found that the FZO sample demonstrates enhanced photodetection parameter values at low bias voltage, showing great potential in optoelectronic applications.

Self-assembly of rylene-decorated guanine ribbons on graphene surface for optoelectronic applications: a theoretical study

We are witnessing a change of paradigm from the conventional top-down to the bottom-up fabrication of nanodevices and particularly optoelectronic devices. A promising example of the bottom-up approach is self-assembling of molecules into layers with predictable and reproducible structural, electronic and optical properties. Nucleobases possess extraordinary ability to self-assembly into one-, two-, and three-dimensional structures. Optical properties of nucleotides are not suitable for wider application to optoelectronics and photovoltaics due to their large optical band gap, which is in contrast to rylene-based dyes that have been intensively investigated in organic optoelectronics. However, these lack the self-assembly capability of nucleobases. Combinations of covalently decorated guanine molecules with rylene type chromophores present ‘the best of the both worlds’. Due to the large size of such compounds and its flexible nature their self-assemblies have not been fully understood yet. Here, we use a theoretical approach to study the structural, energetic and optical properties of rylene-based dye decorated guanine (GPDI), as self-assembled on a graphene sheet. Particularly we utilize the density-functional based tight-binding method to study atomic structure of these systems including the potential energy surface of GPDI and stability and organization of single- and multilayered GPDIs on graphene sheet. Using density-functional theory (DFT) we employ the energy decomposition analysis to gain a deeper insight into the contributions of different moieties to stability of GPDI films. Using time dependent DFT we analyze optical properties of these systems. We find that atomically thin films consisting of only a few molecular layers with large surface areas are more favorable than isolated thick islands. Our study of excited states indicates existence of charge separated states similar to ones found in the well-studied hydrogen bonded organic frameworks. The self-assembly characterized with a large homogeneous coverage and long-living charge-separated states provide the great potential for optoelectronic applications.

In situ passivation of Ga x In(1−x)P nanowires using radial Al y In(1−y)P shells grown by MOVPE

Ga x In(1−x)P nanowires with suitable bandgap (1.35–2.26 eV) ranging from the visible to near-infrared wavelength have great potential in optoelectronic applications. Due to the large surface-to-volume ratio of nanowires, the surface states become a pronounced factor affecting device performance. In this work, we performed a systematic study of Ga x In(1−x)P nanowires’ surface passivation, utilizing Al y In(1−y)P shells grown in situ by using a metal-organic vapor phase epitaxy system. Time-resolved photoinduced luminescence and time-resolved THz spectroscopy measurements were performed to study the nanowires’ carrier recombination processes. Compared to the bare Ga0.41In0.59P nanowires without shells, the hole and electron lifetime of the nanowires with the Al0.36In0.64P shells are found to be larger by 40 and 1.1 times, respectively, demonstrating effective surface passivation of trap states. When shells with higher Al composition were grown, both lifetimes of free holes and electrons decreased prominently. We attribute the acceleration of PL decay to an increase in the trap states’ density due to the formation of defects, including the polycrystalline and oxidized amorphous areas in these samples. Furthermore, in a separate set of samples, we varied the shell thickness. We observed that a certain shell thickness of approximately ∼20 nm is needed for efficient passivation of Ga0.31In0.69P nanowires. The photoconductivity of the sample with a shell thickness of 23 nm decays 10 times slower compared with that of the bare core nanowires. We concluded that both the hole and electron trapping and the overall charge recombination in Ga x In(1−x)P nanowires can be substantially passivated through growing an Al y In(1−y)P shell with appropriate Al composition and thickness. Therefore, we have developed an effective in situ surface passivation of Ga x In(1−x)P nanowires by use of Al y In(1−y)P shells, paving the way to high-performance Ga x In(1−x)P nanowires optoelectronic devices.

Stability enhancement of Cs3Cu2I5 powder with high blue emission realized by Na+ doping strategy

Cesium copper iodide compound (Cs3Cu2I5) is in a blossoming status owing to its advantages of high photoluminescence quantum yield (PL QY), non-toxicity and low-cost, which holds great potential in optoelectronic applications. The issue of long-term stability of Cs3Cu2I5 should be concerned before its commercialization. Herein, we fabricate ultra-stable Cs3Cu2I5 powder by adopting Na + ions doping strategy, achieving great improvements in the air-, photo- and thermal stabilities, and the PL intensity enhancement is also obtained possibly due to the formation of a stronger chemical interaction between Cu+ and I− ions upon Na+ doping, which potentially helps to stabilize both Cu+ cations and I− anions by restraining the diffusion of these ions and prevent Cu+ from oxidizing into Cu2+ from the X-ray photoelectron spectroscopy (XPS) results. We find that Cs3Cu2I5: Na with the doping concentration of 7.4% displays the best performance, its air-, photo-, and thermal stabilities exhibit great improvements. In addition, the PL intensity of Cs3Cu2I5: 7.4% Na powder gets significantly enhanced by 17.4% compared with the undoped Cs3Cu2I5 powder. Moreover, the performance of the UV pumped phosphor converted LEDs (pc-LEDs) based on Cs3Cu2I5: 7.4% Na powder as phosphor also slightly improved compared with the undoped Cs3Cu2I5 based device. Above all, this work is expected to promote the commercialization process of copper-based compounds with excellent stabilities and high emission.

Enhanced interlayer coupling and efficient photodetection response of in-situ grown MoS2–WS2 van der Waals heterostructures

Currently, 2D layered material (2DLM) based heterostructures, also known as van der Waals (vdW) heterostructures, are actively pursued owing to their great potential for optoelectronic applications. They are produced either by vertical stacking of individual layers or via in-plane stitching of 2DLMs. Producing vdW heterostructures with clean interfaces and growing them using direct growth methods are challenging. Herein, we report successful growth of large-area MoS2–WS2 vdW heterostructures (single- to few-monolayer, ML, the thickness of MoS2 and WS2) on oxidized Si (100) substrates using the catalyst-free Pulsed Laser Deposition technique. The in-plane (E12g) and out-of-plane (A1g) Raman-active phonon modes are used to probe the interlayer interactions between the constituent 2D layers. We observe a blueshift of 4.73 (1.63) cm−1 of the A1g peak corresponding to MoS2 (WS2) in the MoS2(1ML)–WS2(1ML) heterostructure compared to 1.27 (0.88) cm−1 for the homo-bilayers. The E12g mode also exhibited blueshift for the heterostructure and redshift for the bilayer of the constituent material. We show that the broadband photodetectors fabricated utilizing in situ grown MoS2–WS2 heterostructures exhibit responsivity, specific detectivity, and current on/off ratio as high as 2.51 × 105 A/W, 4.20 × 1014 Jones, and 1.05 × 105, respectively, under 24 μW/cm2 at 405 nm excitation. The successful fabrication of vdW heterostructures using a simple and scalable direct growth method and excellent photodetector performance pave the way for exploitation of their application potential and offer a playground to test some of the theoretical predictions.

Highly stable CsPbBr3 perovskite quantum dots incorporated in aluminum stearate

CsPbBr3 perovskite quantum dots (PQDs) have drawn much attention for their high photoluminescence quantum yield and great potential in optoelectronic applications. However, they suffer from poor stability under humid condition. This paper reports CsPbBr3 PQDs incorporated in aluminum stearate (AlSt3) matrix via an improved co-precipitation approach, in which AlSt3 not only acted as hydrophobic matrix to protect CsPbBr3 PQDs from surrounding environment, but also passivated the surface of PQDs via the coordination bond of St-Cs and St-Pb, as well as bond between Al3+ and Br−. By this method, the as-synthesized CsPbBr3-AlSt3 composites exhibited excellent stability in ambient condition even directly in water for more than 60 days. With the CsPbBr3-AlSt3 composites (green emission) used as color-conversion layer, a white light-emitting diode (WLED) was fabricated with a high color rendering index (Ra) of 90 and a low color temperature (Tc) of 4929 K. These results suggest that this method pave an effective way to stabilize CsPbBr3 PQDs, which is of great importance for their further application.

Shape-controlled synthesis of Ag/Cs4PbBr6 Janus nanoparticles

The poor light absorption of visible light for Cs4PbBr6 nanocrystals (NCs) has severely impeded their practical applications. Although the semiconductor/perovskite heterostructure holds great promise for enhancement in absorption, it has remained a serious challenge for synthesizing a semiconductor/perovskite heterostructure. In this work, monodispersed Janus heterostructures composed of Cs4PbBr6 decorated with either multiple Ag or single Ag on its surface (named as mAg/Cs4PbBr6 and sAg/Cs4PbBr6 respectively), are successfully prepared. The size of Ag seeds has an important effect on the shape of the products. Small-sized Ag seeds lead to the formation of mAg/Cs4PbBr6 Janus NCs, while relatively large-sized Ag seeds produce sAg/Cs4PbBr6 Janus NCs. It is noted that this work not only provides a novel method for the modification of individual Cs4PbBr6 NCs, but also enhances the absorption of the Cs4PbBr6 in the visible region, indicating great potential for optoelectronic applications, such as photocatalysis and solar cells.

Space‐Confined Growth of 2D InI Showing High Sensitivity in Photodetection

AbstractLayered InI has a great potential in optoelectronic applications due to its direct wide tunable bandgap. However, there is no single report about its 2D synthesis. Here, the growth of high‐quality and ultrathin InI flake (as thin as 8 nm) is reported via space‐confined physical vapor deposition. Impressively, an InI flake‐based photodetector exhibits an ultralow off‐state current of ≈4.2 × 10−12 A, high on/off photocurrent ratio of 104, excellent detectivity of 4.2 × 1012 Jones, a high‐speed response time of 10 ms, as well as excellent effective quantum efficiency of 1600%, suggesting its promising applications in optoelectronics.

Anisotropy of Excitons in Two-Dimensional Perovskite Crystals.

Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (C4H9NH3)2PbI4 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (C4H9NH3)2PbI4 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.