Electron Trap States Research Articles

Degradation-related defect level in weathered silicon heterojunction modules characterized by deep level transient spectroscopy

Commercial silicon heterojunction photovoltaic modules, known as amorphous-silicon-based heterojunction with intrinsic thin-film layer (HIT) modules, show average degradation after 10 years in the field. HIT modules weathered outdoors in Colorado and Florida display mostly uniform decreases in intensity when mapped with photoluminescence (PL) imaging compared to a control module. Flash-table-based current-voltage curves show that degradation is dominated by voltage loss. Samples are cored from each of the modules, and deep level transient spectroscopy (DLTS) detects three electron-trap defect states in all modules with activation energies of electron emission from the defects of 0.07, 0.16, and 0.50 eV. DLTS measurements on the weathered modules show an additional deep-level, electron-trap defect state with an activation energy of 0.51 eV and a trap density of approximately 1012 cm−3. The capture rate is measured using varying short filling pulse times, and the resulting capture cross section is estimated to be 1.1x10−16 cm2. The development of the weathering-related defect level correlates to decreases in carrier lifetime, PL intensity, and module voltage. Various depths of the space charge region are probed with increments in applied reverse bias and filling-pulse bias. This DLTS depth profiling shows a trend of trap density increasing with less applied reverse bias, suggesting that the weathering-related defect increases carrier recombination toward the interface between the bulk silicon wafer and the junction-forming amorphous-silicon passivation layers.

Investigation of Trap Density Effect in Gate-All-Around Field Effect Transistors Using the Finite Element Method

Trap density refers to the density of electronic trap states within dielectric materials that can capture and release charge carriers (electrons or holes) in a semiconductor channel, affecting the transistor’s performance. This study aims to investigate the influence of trap density on the electrothermal behavior of nanowire gate-all-around GAAFET devices. The numerical solution of Poisson’s equations and continuity equations, coupled with the heat conduction model, has been used to predict the temperature inside the GAAFET device. The finite element method has been used to discretize the semiconductor equations. Investigations have been carried out on a number of physical and geometric parameters, such as oxide thickness, nanowire radius, and gate length. Their effects on output characteristics and device temperature have been discussed. A thinner oxide thickness, lower device radius, and longer channel length led to a higher current flow. Results also reveal that high trap densities can have significant impacts on the degradation of electronic devices, particularly in the context of semiconductor devices like transistors.

Investigations of defects in TiO2/HgTe/MoO3 heterostructures and their influence on transport properties

The need for simple-to-manufacture, solution-processable, tunable infrared active optoelectronic materials led to the development of infrared colloidal quantum dots, whose band gaps may be easily regulated by dimensional constraints resulting from the quantum confinement. Due to electronic deep-level trap states that limit effective mobility and function as effective recombination centers, nanocrystal (NC)-based optoelectronic devices still perform less well than what is predicted theoretically. The performance of NC-based optoelectronic devices can be considerably improved by identifying and passivating these defect levels. In this study, we use low-temperature I–V, C–V, C–F and the microcontroller-based deep level transient spectroscopy (DLTS) system to investigate the defect levels in the FTO/TiO2/HgTe/MoO3/Au device. The I–V measurements at low temperatures demonstrated the existence of exponential trap states, with an activation energy of 0.24 eV and a trap density of . Low-temperature C–V and C–F measurements established the existence of deep trap states. With DLTS, we have located two deep trap levels (traps 1 and 2), with energies of 0.25 and 0.46 eV, capture cross-sections and and a concentration of , respectively. The surface states at the HgTe NCs and the oxygen vacancies at the TiO2 are the leading causes of the trap levels, which are primarily present at the interface of the TiO2/HgTe heterojunction. The transport mechanism in these heterojunction devices was happening mainly through these interface trap states. Passivating these defect levels is vital to increase the device effectiveness.

Effect of Co3O4-doping on the microstructure and electrical properties of novel ZnO–Cr2O3-based varistor ceramics

Novel ZnO–Cr2O3-based varistor ceramics have superior current-voltage (I–V) characteristics and, do not contain volatile, rare or toxic dopants. The results showed that doping with Co3O4 greatly affected the nonlinearity of the ZnO–Cr2O3-based ceramics, with the highest coefficient of nonlinearity α equal to 73, while the leakage current was lower than 0.2 μA/cm2. Such a varistor performance enhancement was explained by the substitution of Co2+ into the Zn sites leading to the formation of Zn interstitials and free charge carriers of ZnO grains as well as an increased concentration of electron-trapping interface states like adsorbed oxygen and consequently substantially increased electrostatic barriers at the grain boundaries. The optimal amount of added Co3O4 for high-performance ZnO–Cr2O3-based varistor ceramics was about 0.5 mol.%.

Antithermal Quenching and Multiparametric Temperature Sensing from Mn2+/Tb3+‐Codoped Ca2LaTaO6 Phosphor

Luminescence thermometry plays significant roles in various fields including industrial production, environmental detection, aerospace, and medicine. However, its accuracy improvement remains highly challenging due to the thermal quenching effect of phosphors. Herein, for the first time, a thermal‐activated electron compensation Mn2+‐ and Tb3+‐codoped Ca2LaTaO6 phosphor is developed for multiparametric temperature sensing with tunable emission of Mn2+ and antithermal quenching emission of Tb3+, leading to excellent accuracy at high temperatures. By virtue of the deep electron trap states induced by Mn2+ dopant, the electrons in the deep trap can be thermally activated at high temperatures, which can replenish the attenuated Tb3+ emission caused by thermal quenching, thus bringing out the antithermal quenching phenomenon. On account of the prominent emission properties, the luminescence intensity ratio (LIR) readout and lifetime‐based thermometry are designed, providing a maximum relative sensitivity SR of 3.603% and 1.941% K−1, respectively. Multiparametric temperature sensing and novel data analysis are also employed to further improve the accuracy of the luminescence thermometer. The outstanding relative thermal sensitivity ranging from 8.72% to 16.11% K−1 and temperature uncertainty order of 10−3 are achieved. These results demonstrate that the designed Ca2LaTaO6:Mn2+/Tb3+ phosphor material is a promising thermal‐sensing candidate.

Photocatalytic Production of Syngas from Biomass.

ConspectusAs a renewable solar energy and carbon carrier, biomass exploration has received global attention. Photocatalytic valorization of biomass into fuels and chemicals is a promising and sustainable method for future chemical production. Photocatalysis has the potential to accomplish reactions under ambient conditions due to the unique reaction mechanisms involving photoinduced charge carriers and has recently been recognized as an efficient and feasible technology for biomass conversion. Biomass is widely used as sacrificial agent to scavenge holes in photocatalytic hydrogen evolution, and the carbon is eventually degraded to CO2 with a minor amount of CO. The generation of CO instead of CO2 is more economical and promising but also a challenge under photoreforming conditions.This is a new research direction, while until now there has still been the lack of a comprehensive review article to summarize and provide prospects for this topic. This Account will highlight our contributions in the research direction of the photocatalytic reforming of biomass into syngas (CO + H2). In 2020, we first reported the photocatalytic conversion of biopolyols and sugars into syngas by employing a defect-rich Cu-TiO2 nanorod photocatalyst and found that formic acid is a key intermediate to CO. Further study revealed that a facet-dependent electron-trapping state on anatase TiO2 will affect the photocatalytic dehydration activity for formic acid intermediates by regulating the electron transfer process during the reaction, and the selective generation of FA or CO from photocatalytic biomass reforming was achieved via exposing the (100) or (101) facets, respectively. Visible light-driven syngas generation was further achieved over a CdS-based photocatalyst. Sulfate modification of CdS ([SO4]/CdS) was constructed as the proton acceptor, thus efficiently facilitating the proton-coupled electron transfer process. Besides, we put forward an oxygen-controlled strategy to increase the CO generation rate without a significant decrease in CO selectivity via controlling the O2/substrate ratio. Based on this system, a Z-scheme CdS@g-C3N4 core-shell structure and CdO-CdS semicoherent interface were created to facilitate charge transfer and enhance the O2 activation, thus increasing the CO generation rate. Moreover, we also developed a photoelectrochemical approach to separately produce CO and H2 from biomass. Nitrogen doping of a hexagonal WO3 nanowire array was used to produce the photoanode. The built-in electric field generated via nitrogen doping promoted charge transfer, hence improving the efficiency of PEC reforming of biopolyols and sugars. This Account will systematically analyze the challenges in this research direction, the reaction route in the photocatalytic biomass reforming, and the factors affecting CO selectivity and give insight into the design of efficient photocatalytic systems.

Z-scheme heterojunction of graphitic carbon nitride and calcium ferrite in converter slag for the photocatalytic imidacloprid degradation and hydrogen evolution

Graphitic carbon nitride/ converter slag (gCN/CS) composites were fabricated as photocatalysts by a simple co-calcination. The structural, optical, and physicochemical characteristics of graphitic carbon nitride/ artificial converter slag (gCN/artCS) composites were investigated for the photocatalytic degradation of imidacloprid under visible light irradiation to optimize the mixing ratio of converter slag. The optimized gCN/artCS composite containing 11.58 % of artCS exhibited a 2.5 times faster rate of imidacloprid degradation over 120 min compared to pure gCN. The enhanced separation and transportation of photoinduced electrons and holes were revealed for the optimized gCN/artCS composite by the photoluminescence, impedance spectroscopy, and photocurrent densities. Furthermore, the energy-resolved distribution of electron traps (ERDT) pattern for the optimized composite strongly suggested the development of an interfacial Z-scheme heterojunction between gCN and iron oxide included in artCS, leading to reducing electron-hole pair recombination. Finally, the real CS was applied for the fabrication of the composite with gCN, and then the composite (gCN/realCS) was evaluated for H2 evolution. The H2 evolution rate over gCN/realCS did not come up to gCN/artCS but was greater than the pristine gCN. The reason is possibly due to lacking the electron trap states around 2.0–2.6 eV on the ERDT pattern for gCN/realCS. Thus, the present gCN/CS composites can be a potentially effective photocatalyst for hydrogen evolution under light irradiation.

Surface electron modulation of a plasmonic semiconductor for enhanced CO2 photoreduction

Plasmonic Bi2WO6 nanodots with oxygen vacancy-induced electron trapping states were controllably grown on TiO2 nanosheets as plasmonic heterostructures to break the limitation of surface depletion layer for efficient photocatalysis.

Crystalline Phases Regulate Electronic Trap States at Defective Surfaces of Lead Halide Perovskites.

The role of organic cations in A-sites of lead halide perovskites (LHPs) on carrier dynamics has been debated in an effort to understand the remarkable properties in these materials. However, the change of A-site species in LHPs often leads to the variation of crystalline phases at room temperature. Herein, we combine density functional theory (DFT) and time-dependent DFT methods to study electron traps in CH3NH3PbI3 which exhibits different structural phases with temperature and in APbBr3 [A = CH3NH3, CH(NH2)2, or Cs] with their crystalline phases at room temperature. Regardless of halide species, electron traps arising from halide vacancies at surfaces are spatially localized in tetragonal phase and turn to be rather delocalized in orthorhombic and cubic phases. The reason is revealed by analyzing the projected p orbitals of Pb atoms at conduction band edges, providing a novel strategy of healing surface defects to improving the performances of the LHP solar cells.

Tailored Self-Assembled Monolayer using Chemical Coupling for Indium-Gallium-Zinc Oxide Thin-Film Transistors: Multifunctional Copper Diffusion Barrier.

Controlling the contact properties of a copper (Cu) electrode is an important process for improving the performance of an amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) for high-speed applications, owing to the low resistance-capacitance product constant of Cu. One of the many challenges in Cu application to a-IGZO is inhibiting high diffusivity, which causes degradation in the performance of a-IGZO TFT by forming electron trap states. A self-assembled monolayer (SAM) can perfectly act as a Cu diffusion barrier (DB) and passivation layer that prevents moisture and oxygen, which can deteriorate the TFT on-off performance. However, traditional SAM materials have high contact resistance and low mechanical-adhesion properties. In this study, we demonstrate that tailoring the SAM using the chemical coupling method can enhance the electrical and mechanical properties of a-IGZO TFTs. The doping effects from the dipole moment of the tailored SAMs enhance the electrical properties of a-IGZO TFTs, resulting in a field-effect mobility of 13.87 cm2/V·s, an on-off ratio above 107, and a low contact resistance of 612 Ω. Because of the high electrical performance of tailored SAMs, they function as a Cu DB and a passivation layer. Moreover, a selectively tailored functional group can improve the adhesion properties between Cu and a-IGZO. These multifunctionally tailored SAMs can be a promising candidate for a very thin Cu DB in future electronic technology.

Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX2 (X = S, Se).

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX2 (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS2, while a Se vacancy introduces both hole and electron trap states in ReSe2. Photoexcited electrons and holes can be rapidly captured by these defect states, while the release process is slow, which contributes to an elongated photocarrier lifetime. The suppressed charge carrier recombination lies in the vacancy-induced low-frequency phonon modes that weaken electron-phonon coupling, as well as the reduced overlap between electron and hole wave functions that decreases nonadiabatic coupling. This work provides physical insights into the charge carrier dynamics of 2D ReX2, which may stimulate considerable interest in using defect engineering for future optoelectronic nanodevices.

Facet-Dependent Electron Transfer Regulates Photocatalytic Valorization of Biopolyols.

The electron transfer (ET) from the conduction band of the semiconductor to surface-bound species is a key step in the photocatalytic reaction and strongly affects the reactivity and selectivity, while the effect of catalyst surface structure on this process has rarely been explored due to the lack of an effective method. Herein, we have developed a strategy to detect and measure surface electrons' transfer energy to the adsorbates and disclosed a facet-dependent electron transfer energy over anatase TiO2. The photogenerated electrons are shallowly confined in the five-coordinated Ti atom (Ti5c) on the surface of the (101) facet with a transfer energy below 1.0 eV, while deeply confined in the six-coordinated Ti atom (Ti6c) on the subsurface of the (001) facet with a transfer energy higher than 1.9 eV. The different electron trap states strongly affect the ET process, thus regulating the photocatalytic activity. Taking formic acid (FA) dehydration as the probe reaction, a shallow trap of photoexcited electrons on the (101) facet of anatase TiO2 favors the dehydration of FA to CO, while a deep trap of photoexcited electrons on the (001) facet makes FA stable. Based on this knowledge, we successfully controlled the selectivity in the photocatalytic oxidation of biopolyols via selectively exposing the facet of TiO2. Through controlling the (001)/(101) facet, a wide range of biopolyols can be selectively converted into FA or CO with a selectivity of up to 80%. The present work disclosed a facet-dependent electron transfer process and provides a new horizon to the design of photocatalytic systems.

Regulating Lewis acidity and local electron density of iron-based metal organic frameworks via cerium doping for efficient photo-Fenton process

The photo-Fenton performance of Fe-based metal organic frameworks (Fe-MOFs) largely depends on the amount and the local electron density of metal coordinately unsaturated sites (M CUSs). However, a majority of Fe active sites are fully bound by organic ligands leading to decreased Fe CUSs. Additionally, the symmetrical electronic distribution of iron-oxo (Fe-O) clusters and the fast electron-hole recombination are unbeneficial for the directional electron transfer and the following electron accumulation on Fe CUSs. Herein, the structure of Fe-O clusters onto the framework of MIL-88B was controllably regulated via change of Ce doping amount, among which Fe0.8Ce0.2-MIL-88B exhibited highest removal efficiency of tetracycline (TC). That was mainly ascribed to the following two points: for one, the induced ligand missing defects ameliorated the pore structures and generated more M CUSs; for another, the lower electronegativity of Ce than Fe and the role of ligand missing defects as electron trap state collectively increased the local electron density at Fe CUSs. As a result, the increased M CUSs provided more active sites for H2O2 coordination and the highly concentrated electrons density at Fe CUSs afforded the substantial electron donation towards robust H2O2 dissociation into ∙OH. Furthermore, the increased mesoporous size favored highly-efficient utilization of ∙OH. This work provides a facile strategy to improve photo-Fenton performance of Fe-MOFs.

Simple tactic polycondensation synthesis of Z-scheme quasi-polymeric g-C3N4/CaFe2O4 composite for enhanced photocatalytic water depollution via p-n heterojunction

Ferrites are promising photocatalysts as they absorb a considerable fraction of visible light. Herein, a novel in-situ simple tactic polycondensation method was used to produce n-type porous graphitic carbon nitride nanosheets over p-type CaFe2O4 particles resulting in a “quasi-polymeric” heterojunction. An interfacial electron trap state was created, as represented by an energy-resolved distribution of electron trap patterns in the g-C3N4/CaFe2O4, which traps excited electrons and prevents charge carrier recombination. When the CaFe2O4 precursor content in the g-C3N4/CaFe2O4composite was optimized, the degradation rates of ciprofloxacin and phenol are 2.3 and 2.1-fold higher in comparison to pristine g-C3N4, respectively. The g-C3N4/CaFe2O4 composite efficiently absorbed visible light and could separate and transport charge carriers through the p-n heterojunction. The efficient interfacial charge transport and separation achieved in the composite were validated using photoluminescence spectra and photoelectrochemical characterizations. Based on scavenger studies and electron spin resonance analysis, the most active radical species for the aforementioned pollutant degradation are holes and superoxide anion radicals. Mott-Schottky measurements and X-ray photoelectron spectroscopy confirmed the photocatalytic reaction mechanism is a Z-scheme charge carrier transport route based on the p-n heterojunction. Therefore, the g-C3N4/CaFe2O4 heterojunction offers a lot of promise for pollutant degradation that is both efficient and long-term.

2D Bismuthene as a Functional Interlayer between BiVO4 and NiFeOOH for Enhanced Oxygen‐Evolution Photoanodes

AbstractBiVO4 has attracted wide attention for oxygen‐evolution photoanodes in water‐splitting photoelectrochemical devices. However, its performance is hampered by electron‐hole recombination at surface states. Herein, partially oxidized two‐dimensional (2D) bismuthene is developed as an effective, stable, functional interlayer between BiVO4 and the archetypal NiFeOOH co‐catalyst. Comprehensive (photo)electrochemical and surface photovoltage characterizations show that NiFeOOH can effectively increase the lifetime of photogenerated holes by passivating hole trap states of BiVO4; however, it is limited in influencing electron trap states related to oxygen vacancies (VO). Loading bismuthene on BiVO4 photoanodes increases the density of VO that are beneficial for the oxygen evolution reaction via the formation of oxy/hydroxyl‐based water oxidation intermediates at the surface. Moreover, bismuthene increases interfacial band bending and fills the VO‐related electron traps, leading to more efficient charge extraction. With the synergistic interaction of bismuthene and NiFeOOH on BiVO4, this composite photoanode achieves a 5.8‐fold increase in photocurrent compared to bare BiVO4 reaching a stable 3.4 (±0.2) mA cm–2 at a low bias of +0.8 VRHE or 4.7(±0.2) mA cm–2 at +1.23 VRHE. The use of 2D bismuthene as functional interlayer provides a new strategy to enhance the performance of photoanodes.

An Irradiance-Adaptable Near-Infrared Vertical Heterojunction Phototransistor.

Bioinspired artificial visual perception devices with the optical environment-adaptable function have attracted significant attention for their promising potential in applications like robotics and machine vision. In this regard, a photodetector with in-sensor adaptability is longed for in terms of complexity, efficiency, and cost. Here, a near-infrared phototransistor with a benign light irradiance-adaptability is presented. The phototransistor uses a vertically stacking graphene/lead sulfide quantum dots/graphene heterojunction as the conductive channel. Compared with ordinary lead sulfide quantum dots-decorated graphene phototransistors, the present device demonstrates a faster photoresponse speed and an abnormal transfer characteristic. The latter characteristic is induced by the gate voltage-tunable Fermi level in the heterojunction and the abundant electron trap states in the quantum dot film, which jointly results in an intense dependence of the photoresponse on the gate voltage. The dynamic trapping and de-trapping processes in the quantum dot film enable the inhibition or potentiation of the photoresponse, based on which the photopic or scotopic adaptation behavior of the human retina is successfully mimicked, respectively. By providing an irradiance-adaptable photodetector with a spectral response beyond visible light, this work should inspire future research on artificial environment-adaptable perception devices.

Synchronous Surface Reconstruction and Defect Passivation for High-Performance Inorganic Perovskite Solar Cells.

The nonradiative charge recombination caused by surface defects and inferior crystalline quality are major roadblocks to further enhancing the performance of CsPbI3- x Brx perovskite solar cells (PSCs). Theoretical calculations indicate that sodium diethyldithiocarbamate (NaDDTC), a popular bacteriostatic benign material, can initiate multiple interactions with the CsPbI3- x Brx perovskite surface to effectively passivate the defects. The experimental results reveal that the NaDDTC can indeed passivate the electron trap states and lock active sites for charge traps and water adsorption. In addition, it is found that a solid-state reaction is triggered for perovskite crystal regrowth by the NaDDTC post-treatment, which not only enlarges grain size for reducing the density of grain boundary defects but also compensates some surface defects induced by the primary film growth. Consequently, the power conversion efficiency (PCE) of the CsPbI3- x Brx PSC is increased to as high as 20.40%, with significant improvement in fill factor and open-circuit voltage (VOC ), making it one of the highest for this type of solar cell. Furthermore, the optimized devices exhibit better environmental stability. Overall, this robust synchronous strategy provides efficient surface reconstruction and defect passivation for achieving both high PCE and stable inorganic perovskite.

Defect levels in CsPbCl3 single crystals determined by thermally stimulated current spectroscopy

Thermally stimulated current (TSC) spectroscopy was used to characterize electronic trap states in the perovskite CsPbCl3 bulk single crystals which are promising for gamma ray detection. The TSC spectra indicate the presence of multiple traps over the temperature range from 80 K to above room temperature. The possible analytical defects identified were VCs and VCl vacancies and Pbi interstitials that have concentrations of the order of 1011−1016 cm−3 and capture cross sections of ∼10−18 cm2. A comparison of crystals grown from different ingots reveals that the concentration of defects in the crystal with an improved growth procedure is about one to four orders of magnitude less than those of a crystal from an earlier growth process. A further reduction and elimination of trap states within the perovskite ingot should lead to crystals with improved mobilities, carrier lifetimes, and detector response characteristics.

Unveiling the Valence State of Interstitial Bromine on Charge Carrier Lifetime in CH3NH3PbBr3 by Quantum Dynamics Simulation.

Interstitial halogens are detrimental to the optoelectronic properties of metal halide perovskites. Using nonadiabatic (NA) molecular dynamics, we demonstrate that the valence state of interstitial bromine strongly changes the carrier lifetimes of MAPbBr3 (MA = CH3NH3+). Both neutral and negatively charged interstitial bromine create no midgap states, and they decrease the bandgap, weaken the NA coupling, and accelerate decoherence in a different extent with respect to pristine MAPbBr3, making free charge recombination either slow down about a 3-fold or remain largely unchanged. In contrast, a positively charged interstitial bromine forms a Br trimer and introduces a deep electron trap state, causing a 1.4-fold increase of charge recombination followed by a rapid electron trapping or across the bandgap because of an enhanced NA coupling. The simulations uncover the influence of different charged interstitial bromine defects on MAPbBr3 carrier lifetimes and provide rational guidelines for optimizing perovskite solar cells.

Thermally Activated Bright-State Delayed Blue Photoluminescence from InP Quantum Dots.

Thermally activated delayed photoluminescence (TADPL) generated from organic chromophore-functionalized quantum dots (QDs) is potentially beneficial for persistent light generation, QD-based PL sensors, and photochemical synthesis. While previous research demonstrated that naphthoic acid-functionalized InP QDs can be employed as low-toxicity, blue-emissive TADPL materials, the electron trap states inherent in these nanocrystals inhibited the observation of TADPL emerging from the higher-lying bright states. Here, we address this challenge by employing the heterocyclic aromatic compound 8-quinolinecarboxylic acid (QCA), whose triplet energy is strategically positioned to bypass the electron trap states in InP QDs. Transient absorption and photoluminescence spectroscopies revealed the generation of bright-state TADPL from QCA-functionalized InP QDs resulting from a nearly quantitative Dexter-like triplet-triplet energy transfer (TTET) from photoexcited InP QDs to surface-anchored QCA chromophores followed by reverse TTET from these bound molecules to the InP QDs. This modification resulted in a 119-fold increase in the average PL intensity decay time with respect to the as-synthesized InP QDs.