Shallow Defect Levels Research Articles

The effect of SbCl3 treatment on CdTe produced by close space sublimation method

In this study, influence of SbCl3 treatment on CdTe films deposited by the close space sublimation method was investigated. SbCl3 treatment was compared with conventional CdCl2 treated and untreated samples. It was determined that CdTe grew as Cd-rich and there was a slight decrease in Cd-amount after SbCl3 and CdCl2 treatments. In addition, a significant amount of Sb was detected in the SbCl3 treated sample. The samples crystallized in the cubic structure of CdTe. However, graded structures such as phase-I and phase-II with different structural parameters were formed. In the SbCl3 sample, it was revealed that the presence of Sb- caused a slight increase in the lattice parameter, compared to the other samples. Morphological analyses of the samples showed facet and large-small grain structures. CdCl2 treatment caused a slight decrease in grain size, while SbCl3 treatment resulted in a coarser and rougher grain structure. CdCl2 treatment increased transmittance, whereas SbCl3 treatment caused a decrease in transmittance (hence, an increase in absorbance). It was observed that the bandgaps were ∼1.49 eV in all samples, and annealing, as well as CdCl2 and SbCl3 heat treatments did not cause a sharp change in the bandgaps. Photoluminescence spectra revealed the presence of band-edge and shallow-level defect transitions (except CdCl2 treated) in the samples. All results suggest that SbCl3 heat treatment has a significant effect on CdTe and may be an alternative to CdCl2.

Stable NiOx-based inverted perovskite solar cells achieved by passivation of multifunctional star polymer

Perovskite materials have excellent photoelectric properties and are a hot spot in international research. However, there are deep/shallow energy level traps in the grain boundaries (GBs)/surface of perovskite thin films, which affect the optoelectronic performance of perovskite solar cells (PSCs). Here, we design and synthesize a three-dimensional star-shaped polymer with various groups to regulate the light-absorbing layer of perovskite. The eight branched chains of multifunctional star polymer are rich in CO, N = N, N = O, and –CF3 functional groups, which are used to passivate uncoordinated lead ions and to immobilize methylamine, formamidine cations on the GBs/surface of perovskite films. Simultaneous passivation of deep-level defects and suppression the appearance of shallow-level defects on the perovskite surface/GBs, thereby greatly improving the optoelectronic performance of PSCs. Compared with the efficiency of 22.38 % of the reference device, the efficiency of the multifunctional star polymer incorporated inverted device reaches 24.03 %. Moreover, the multifunctional star-shaped polymer modified inverted-encapsulation device also exhibits excellent operational stability, maintaining 80 % of the initial efficiency for more than 5500 h.

Far-infrared transparent conductors

The long-standing challenge in designing far-infrared transparent conductors (FIRTC) is the combination of high plasma absorption edge (λp) and high conductivity (σ). These competing requirements are commonly met by tuning carrier concentration or/and effective carrier mass in a metal oxide/oxonate with low optical dielectric constant (εopt = 2–7). However, despite the high σ, the transparent band is limited to mid-infrared (λp < 5 μm). In this paper, we break the trade-off between high σ and λp by increasing the “so-called constant” εopt that has been neglected, and successfully develop the material family of FIRTC with εopt > 15 and λp > 15 μm. These FIRTC crystals are mainly octahedrally-coordinated heavy-metal chalcogenides and their solid solutions with shallow-level defects. Their high εopt relies on the formation of electron-deficiency multicenter bonds resulting in the great electron-polarization effect. The new FIRTC enables us to develop the first “continuous film” type far-infrared electromagnetic shielder that is unattainable using traditional materials. Therefore, this study may inaugurate a new era in far-infrared optoelectronics.

Efficient Inorganic Vapor-Assisted Defects Passivation for Perovskite Solar Module.

Surface trap as intrinsic defects-mediated non-radiative charge recombination is a major obstacle to achieving the reliable fabrication of high-efficiency and large-area perovskite photovoltaics. Here a CS2 vapor-assisted passivation strategy is proposed for perovskite solar module, aiming to passivate the iodine vacancy and uncoordinated Pb2+ caused by ion migration. Significantly, this method can avoid the disadvantages of inhomogeneity film caused by spin-coating-assisted passivation and reconstruction of perovskite surface from solvent. The CS2 vapor passivated perovskite device presents a higher defect formation energy (0.54eV) of iodine vacancy than the pristine (0.37eV), while uncoordinated Pb2+ is bonded with CS2 . The shallow level defect passivation of iodine vacancy and uncoordinated Pb2+ has obviously enhanced the device efficiencies (25.20% for 0.08cm2 and 20.66% for 40.6cm2 ) and the stability, exhibiting an average T80 -lifetime of 1040h working at the maximum power point, and maintaining over 90% of initial efficiency after 2000h at RH=30% and 30°C.

The Relationship between Photoluminescence Emissions and Photocatalytic Activity of CeO2 Nanocrystals.

In this work, we focus on understanding the morphology and photocatalytic properties of CeO2 nanocrystals (NCs) synthesized via a microwave-assisted solvothermal method using acetone and ethanol as solvents. Wulff constructions reveal a complete map of available morphologies and a theoretical-experimental match with octahedral nanoparticles obtained through synthesis using ethanol as solvent. NCs synthesized in acetone show a greater contribution of emission peaks in the blue region (∼450 nm), which may be associated with higher Ce3+ concentration, originating shallow-level defects within the CeO2 lattice while for the samples synthesized in ethanol a strong orange-red emission (∼595 nm) suggests that oxygen vacancies may originate from deep-level defects within the optical bandgap region. The superior photocatalytic response of CeO2 synthesized in acetone compared to that of CeO2 synthesized in ethanol may be associated with an increase in long-/short-range disorder within the CeO2 structure, causing the Egap value to decrease, facilitating light absorption. Furthermore, surface (100) stabilization in samples synthesized in ethanol may be related to low photocatalytic activity. Photocatalytic degradation was facilitated by the generation of ·OH and ·O2- radicals as corroborated by the trapping experiment. The mechanism of enhanced photocatalytic activity has been proposed suggesting that samples synthesized in acetone tend to have lower e'─h· pair recombination, which is reflected in their higher photocatalytic response.

Effects of defects on electrical transport properties of anatase TiO&lt;sub&gt;2&lt;/sub&gt; polycrystalline under high pressure: AC impedance measurement

The electrical transport properties of anatase TiO&lt;sub&gt;2&lt;/sub&gt; polycrystalline have been systematically investigated by using high pressure &lt;i&gt;in-situ&lt;/i&gt; impedance spectroscopy measurements. The anomalous behaviors of resistance, parameter factor and relaxation frequency of grain and grain boundary can be found at 6.4, 11.5 and 24.6 GPa. The results indicate that the first two discontinuous points (6.4 and 11.5 GPa) correspond to the phase transitions of TiO&lt;sub&gt;2&lt;/sub&gt; from anatase to α-PbO&lt;sub&gt;2&lt;/sub&gt; and then to baddeleyite, respectively. Above 24.6 GPa, TiO&lt;sub&gt;2&lt;/sub&gt; completely transforms into the baddeleyite phase. Based on the change of grain resistance and grain boundary resistance under pressure, intrinsic defects play a crucial effect in the electrical transport properties of TiO&lt;sub&gt;2&lt;/sub&gt; at high pressures. At 6.4 GPa, the occurrence of phase transition gives rise to the variation of defects’ role, from a deep energy level defect (as a recombination centre) changes into a shallow energy level defect (providing carriers for the conduction and valence bands). In addition, the position of defect in energy band changes with pressure increasing. The phase transition of TiO&lt;sub&gt;2&lt;/sub&gt; at 6.4 GPa is the rearrangement of TiO&lt;sub&gt;6&lt;/sub&gt; octahedron, while the other one at 11.5 GPa can be attributed to the migration of oxygen Schottky defects from inner to surface. Combining the packing factor and relaxation frequency, the electrical transport properties of TiO&lt;sub&gt;2&lt;/sub&gt; under pressure are revealed, the packing factor and the relaxation frequency are closely related to the mobility and the carrier concentration, respectively. The activation energy of grain and grain boundary decrease with the pressure elevating, indicating that the transport of carriers in grain and grain boundary become easier under pressure, and the former is smoother than the latter owing to the activation energy of grain being smaller than that of grain boundary in the same pressure range. Moreover, the relaxation frequency ratio of TiO&lt;sub&gt;2&lt;/sub&gt; grain and TiO&lt;sub&gt;2&lt;/sub&gt; grain boundary decreases with pressure increasing, and the grain boundary effect under high pressure is not obvious.

Defects-driven photoconduction in one step direct injection flame synthesized inverse spinel Zn2SnO4 nanoparticles for photodetector applications

Pristine inverse spinel zinc stannate nanoparticles by a rapid and ceaseless one step Direct Injection Flame Synthesis (DIFS) method by utilizing the zinc and tin microparticles as the feedstock is reported. The correlation of mixed morphologies with variation in resident and oxidation time of the reactants in the flame during the synthesis is done by basic Fluid Dynamics equations. The surface level cation (tin and zinc) disordering, lowered conduction band minimum and oxygen vacancies derived shallow level defect states are observed. A simple photodetector is fabricated by coating the zinc stannate nanoparticles over the p-type silicon substrate. The presence of mixed morphologies enhances the light scattering and antireflection. The mechanism of p-silicon/n-zinc stannate photodetector based on chemisorption of atmospheric oxygen species (below band conduction process) with defect assisted recombination charge transport is discussed. High Dark/Photocurrent ratio of 90% and Detectivity of 1.05 × 1010 Jones in visible light photodetection is observed and explained.

First-principles study of detrimental iodine vacancy in lead halide perovskite under strain and electron injection

Vacancy defects are universally regarded to be the main defect that limits the photoelectric conversion efficiency of perovskite solar cells. In perovskite, iodine vacancy dominates the defect proportion due to its low formation energy. However, the defect property of iodine vacancy (VI) is still in dispute. Ideally, the VI defect is considered to be a shallow level defect near conduction band minimum, meaning that it does not act as a Shockley–Read–Hall (SRH) nonradiative recombination center. Herein, we find a direct correlation between compressive strain and VI defect behavior. The compressive strain along the lattice vector b/c direction will drive the VI defect from shallow level to deep level defect, which is related to the formation of Pb-dimer. In addition, the influence of extra electrons is also considered during the structural evolution of VI, which is often observed in the experiments. Therefore, we find that the elimination of compressive strain and extra electrons can be of great significance for improving the photoelectric performance of perovskite solar cells. Our work reveals the defect properties of VI from shallow level one to the SRH recombination center and the inherent physics mechanism of defect evolution under external factors, which provides a strategy to control device defects and eliminate recombination losses.

Unveiling photoluminescent response of Ce-doped CaCu3Ti4O12: An experimental-theoretical approach

CaCu3Ti4O12: x% Ce (x = 0.00, 0.25, 0.50, 0.75, and 1.00) ceramic composites were prepared via solid-state reaction. Theoretical atomistic simulations were combined with experimental techniques to uncover Ce effects in the (micro)structure and photoluminescence of CaCu3Ti4O12-based ceramics. Application of perovskites ceramics in optoelectronics have been limited by their specific, narrow emission range, which compromise operational efficiency, pushing for the development of novel perovskite-emissive materials. This study results confirm that Ce ions are incorporated at Ca sites within the CaCu3Ti4O12 lattice, inducing point metal and oxygen vacancies in the optical bandgap region. Shallow-level defects (VCa′′/VO⦁⦁) were associated with broadband violet-blue photoluminescent (PL) emissions. Better color rendering may be a direct consequence of crystalline field splitting/wider PL emission. Furthermore, results demonstrate that PL on CaCu3Ti4O12: Ce system intensity can be modulated by structural defects, making it promising for applications in optoelectronics.

Electronic properties and defect levels induced by [formula omitted]-type defect-complexes in Ge

Defect-complexes are point defects that significantly influence the geometric, optical, and electrical properties of materials. Defect-complexes are known to improve the electronic and electrical properties of Ge. Deep and shallow defect levels in Ge have been linked to defect-complexes formed by the double self-interstitials and rare earth atoms. Despite this breakthrough, several defect-complexes in Ge are not well understood; hence may pose as a challenge to the optimal performance of Ge based devices. In this study, we present the results of the hybrid density functional theory calculations of substitutional and interstitial defect-complexes (BGeNi, NGeBi, AlGePi, PGeAli, GaGeAsi, AsGeGai, InGeSbi, and SbGeIni) in Ge. Their formation energies, electronic properties, defect-complex stability and induced defect levels in Ge were predicted. While the formation energies of the defect-complexes formed by the P and Al atoms were relatively low and energetically more favourable, those defect-complexes formed by the B and N atoms were the least energetically favourable. Except for the BGeNi, all the defect-complexes significantly bound with energies lower than their formation energies. The NGeBi and PGeAli essential donor levels were in the band gap of Ge. A shallow double acceptor defect level was found to be associated with the AlGePi, while the InGeSbi induced a shallow double donor defect level. The electrical inactive defect-complexes were the BGeNi, GaGeAsi, AsGeGai and SbGeIni. The results of this report are important, as they provide theoretical insight of the prediction of the n/p-type substitutional and interstitial defect-complexes in Ge.

Ion migration suppression mechanism via 4-sulfobenzoic acid monopotassium salt for 22.7% stable perovskite solar cells

The deep-level traps at grain boundaries (GBs) and halide ion migration are quite challenging for further enhancement of the stability and efficiency of perovskite solar cells (PSCs) as well as for the elimination of notorious hysteresis. Herein, we report a large-sized strongly coordinated organic anion GB anchoring strategy for suppressing ion migration and passivating defects in planar PSCs. The practical implementation of this strategy involves the incorporation of potassium salts containing a large-sized organic counter anion (4-sulfobenzoic acid monopotassium salt, SAMS) into the perovskite precursor. It has been found that anions within SAMS can be firmly anchored at GBs due to the strong coordination interaction between C=O and/or S=O at both ends of bulky anion and undercoordinated Pb2+ and/or halide vacancies, along with the hydrogen bond between −OH and formamidinium. SAMS can not only passivate shallow-level defects but also cause more effective passivation of the deep-level defects. The GB manipulation strategy results in a reduced defect density, an increased carrier lifetime as well as suppressed ion migration, which in turn contributed to enhanced efficiency and stability of PSCs together with a thorough elimination of hysteresis. As a result, the SAMS-modified device with an outstanding fill factor of 0.84 delivers a significant improvement in efficiency (22.7%) in comparison with the control device (20.3%). The unencapsulated modified device demonstrates only little degradation after 1320 h at 60°C.

Research Progress of High-Sensitivity Perovskite Photodetectors: A Review of Photodetectors: Noise, Structure, and Materials

In recent years, perovskite materials have been widely used in optoelectronic components due to a series of advantages such as a high light absorption coefficient, high carrier mobility, long carrier diffusion length, shallow defect level, and high crystallinity. The photodetector is an important photoelectric device that can convert light radiation signals into electrical signals, so it has significant applications and scientific research value in military, civil, and other fields. Semiconductor materials are an essential part of photodetectors. So far, many semiconductor materials have been used in photodetectors, including silicon, carbon nanotubes, III–V compounds, and quantum dots, and remarkable progress has been made in improving the light detection performance and device structure design. However, photodetectors based on these materials usually require expensive materials, rigorous processes, and complex manufacturing conditions, which hinder their commercial application. Optoelectronic devices based on perovskite materials have the advantages of a simple fabrication process, low cost, and high performance, making them widely considered in optoelectronic applications. This review focuses on the preparation and photoelectric performance of the perovskite photodetector and the effect of noise on the performance of the perovskite detector and how to reduce the detector’s noise to increase the detection rate. In this review, we mainly discuss the following four aspects of work. First, we discuss the various noises of perovskite photodetectors. Then, we explore ways to reduce the noise of perovskite detectors with different structures (photoconductor, photodiode, and phototransistor). We explore corresponding improvement methods for different device structure detectors to reduce noise and improve the detection performance. Next, we discuss the different synthesis methods of all-inorganic perovskites, including solution processing synthesis, vapor-assisted solution synthesis, and chemical vapor deposition. Finally, current challenges of perovskite photodetectors (toxicity, stability, flexibility, and self-powered) are summarized and prospected.

Sulfonic Zwitterion for Passivating Deep and Shallow Level Defects in Perovskite Light‐Emitting Diodes

AbstractChemical passivation via functional additives plays a critical role in achieving high performance perovskite light‐emitting diodes (PeLEDs). Here, perovskite composite films for high performance PeLEDs by using zwitterion 3‐aminopropanesulfonic acid (APS) as the additive are developed. The sulfonic group of APS can simultaneously passivate deep and shallow level defects in perovskites via coordinate and hydrogen bonding, which leads to suppressed non‐radiative recombination and ion migration in the perovskite composite films. Based on this, PeLEDs with a peak external quantum efficiency of 19.2% and a half‐lifetime of 43 h at a constant current density of 100 mA cm−2 are obtained, representing one of the most stable and efficient PeLEDs under high current densities.

Bridge role of weak chemical bonding in photocatalytic performance of asymmetric 2H-MoS2/BiOCl Janus heterostructure

The geometric and electronic structure, partial (band decomposed) charge density, charge transfer, electron localization function and photocatalytic mechanism of the asymmetric 2H-MoS2/BiOCl Janus heterostructure were systematically studied with first-principles density functional theory. Our calculations showed that there exist several newly formed weak Bi-S bonds with shorter bond lengths between BiOCl and 2H-MoS2 which act as an electron transport bridge along the direction perpendicular to the heterojunction interface. This newly weak bonds lead to the formation of occupied shallow defect levels approximately 0.0–0.9 eV below the bottom of the conduction band. Electrons located at these defect levels can easily jump into the conduction band as a donor energy level under thermal fluctuations and simultaneously further promote the effective separation of photo-generated electron-hole pairs in the BiOCl. The photogenerated electrons located around Bi-atom layer in the conduction band of BiOCl transfer to the valence band of 2H-MoS2 around the S-atom layer through the interface of the asymmetric 2H-MoS2/BiOCl Janus heterostructure, which significantly reduce photo-generated holes in the 2H-MoS2 and electrons in the BiOCl. The large numbers of photogenerated electrons from the 2H-MoS2 cannot recombine with holes owing to lack of sufficient holes. They will move to the surface and greatly improve the hydrogen production activity in the 2H-MoS2. While the photogenerated holes from the BiOCl will significantly improve the ability of BiOCl to oxidize pollutant in the water owing to the absence of sufficient electrons. Our studies provide new way for the design of asymmetric Janus double-layer heterostructures with newly formed weak chemical bonding.

Progress of defect and defect passivation in perovskite solar cells

Research on perovskite solar cells is prevalent because of their excellent photovoltaic performance. Most of the perovskite films are prepared by polycrystalline perovskite films and low-temperature solution method, thus inevitably creating a high density of defects, including point defects and extended defects. These defects can also be divided into two types: shallow-level defects and deep-level defects. The multiple types of defects are the main cause of nonradiative recombination, which will limit the enhancement of photovoltaic properties and stability of solar cell devices. In this paper, we review the latest advances in defect passivation and describe in detail the mechanisms of different methods to passivate defects at the surface and interface of perovskite films to reduce nonradiative recombination. We also summarize the research results about the defect passivation to reduce the deep energy level traps by Lewis acid and base, anion and cation, and the results about the conversion of defects into wide band gap materials as well. The effects of various strategies to modulate the mechanism of passivation of perovskite surface/interface defects are also elaborated. In addition, we discuss the intrinsic link between crystal defects and device stability, and provide an outlook on the feasibility of defect passivation strategies in future research.

Influence of current conduction paths and native defects on gas sensing properties of polar and non-polar GaN

The CO gas sensing characteristics of polar GaN (P–GaN) and non-polar GaN (NP–GaN) thin-films grown by RF–plasma assisted molecular beam epitaxy on c–Al2O3 and r–Al2O3 substrate is analyzed. The temperature-dependent (27–300 °C) current-voltage (I–V) measurements were performed for both (P–GaN & NP–GaN) Schottky barrier diodes having identical device dimensions with Au as the metal contact. The Schottky barrier height increases with the increment in temperature, while vice versa was perceived for the ideality factor and series resistance. The I–V characteristics dictated that the terminal current for P–GaN is 25 times that of NP-GaN, further corroborated by simulation results. The I-V curve fitting suggests the initial emission of charge carrier from a trapped state to a continuum of electronic state, following the Frenkel-Poole emission model for P-GaN. The NP–GaN demonstrated a higher surface-to-volume ratio and native (shallow and deep level) defects corresponding to VGa and ON as compared to the P–GaN. The sensing response obtained for the NP–GaN for 100 ppm CO gas at 300 °C is ~ 33%, which is about seven times the response in the case of P–GaN. The role of native defects and the potentiality of the fabricated NP–GaN over P–GaN films in providing a better sensing characteristic by reducing the current conduction paths are elaborated.

Electronic properties of intrinsic vacancies in single-layer CaF2 and its heterostructure with monolayer MoS2

Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF2 single layer and its heterostructures with monolayer MoS2 are investigated from first-principles calculations. VCa introduces a shallow defect level close to the VBM, whereas VF introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, VF has a relatively lower formation energy than VCa, except for the extreme Ca-rich case. Thus, VF should be dominant in CaF2. The band offset between CaF2 and MoS2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF2, the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF2 to MoS2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS2, and the electronic properties of MoS2 are almost intact. Compared with h-BN that has a small valence band offset with MoS2 and could introduce in-gap defect states, CaF2 can be a good candidate to serve as the dielectric layer of MoS2-based transistors.

Quantitative analysis of defect states in amorphous InGaZnO thin-film transistors using photoinduced current transient spectroscopy

The device and defect characteristics of amorphous indium–gallium–zinc oxide (In:Ga:Zn = 1:1:1 at.%) thin-film transistors (TFTs) as a function of the oxygen partial pressure were investigated. It was found that as the oxygen partial pressure increased, the field effect mobility decreased, the threshold voltage saw a positive shift, and this shift of threshold voltage increased under a negative gate bias stress. From our qualitative analysis of defect states below the conduction band, it was found that as the oxygen partial pressure increased, defect states in the shallow levels decreased, while defect states in the deep levels increased. A quantitative analysis of the defect states in the TFT structures was conducted using photoinduced current transient spectroscopy. It was found that as the oxygen partial pressure used during fabrication of the TFTs increased from 0% to 10% to 60%, the defect states in the shallow levels decreased from 2.74 × 1018 to 2.93 × 1017 to 3.55 × 1016 cm−3, while the defect states in the deep levels increased from non-availability to 1.86 × 1016 to 3.25 × 1016 cm−3. As the oxygen partial pressure increased, the decrease in shallow level defect density is strongly related to a decrease in carrier concentration; the increase in deep level defect density affects the mobility and causes device instability.

Thickness induced modifications in the valence, conduction bands and optoelectronic properties of undoped and Nb-doped anatase TiO2 thin films

Nb-doped anatase TiO2 (NTO) is a promising wide band gap transparent semiconductor as it is an inexpensive, environment-friendly and chemically stable compound. However, its overall electronic structure and optoelectronic properties are tailored by tuning the microstructure, which are effected by varying process conditions. To this end, here series of thickening NTO and undoped anatase TiO2 (TO) films are deposited on quartz substrate in RF magnetron sputtering, followed by vacuum annealing at 823 K. Following fabrication, detailed electronic structure, defect states, microstructure and optoelectronic characterization of all these films are performed. Here, energy positions of the valence and conduction band edges are correlated with the oxygen and titanium content of these films. Whereas, TO films are found to be highly insulating, NTO films show highly conducting characteristics. The lowest electrical resistivity of 4.80 × 10−3 Ω cm is obtained for ~74 nm thick NTO film. Additionally, relative positions and intensities of the shallow donor level defect states of anatase are analyzed and compared with ZnO to gain fundamental insight into the differences in their electrical behavior. Along with visible region, these films also exhibit high transmittance in NIR range, thereby making these promising transparent conductors in the entire spectral range.

Orange Photoluminescence from Hydrothermally Grown Zno Nanorods and Study on its Defects

The visible photoluminescence (PL) of ZnO is controversial for a long time. At present, the contribution of oxygen interstitial defects to yellow/orange emission from ZnO nanostructures is on debate. In this report, the origin of orange emission from solution- grown ZnO nanorods is investigated using excitation wavelength dependent photoluminescence PL, PL excitation and UV-Vis spectra. These results showed that orange emission may be due to the transition of an electron from shallow defect levels positioned slightly below the conduction band to the singly ionized oxygen vacancies. Hence, it is believed that oxygen interstitials may not be responsible for orange emission from solution grown ZnO nanostructures.