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The evolution of various point defects in 100 keV Li ion-implanted ZnO nanorods by varying the fluences from 1 × 1014 to 7 × 1015 ions per cm2 has been investigated experimentally and using a theoretical Monte Carlo simulation code named SRIM.

Transparent conducting (TC) films based on Al and In co-doped ZnO (AIZO) are deposited at room temperature (RT) onto glass as well as flexible polyethylene terephthalate (PET) substrates by pulsed laser deposition (PLD) technique. While substrate heating becomes inevitable to obtain enough conductivity of the oxide films, we simply by controlling the chamber O2 pressure (3 × 10–3 to 1.5 × 10–2 mbar) have achieved the desired structural, electrical and optical properties of the AIZO films without the need to heat the substrate. All the co-doped films having hexagonal wurtzite structure of ZnO shows surface roughness values in the range of 2.3–4.4 nm. The average transparency of the films is 79–92% in the 400–700 nm range. The film deposited at O2 pressure of 3 × 10–3 mbar on glass substrate shows the highest carrier concentration value of 1.60 × 1021 cm−3 with the lowest sheet resistance of 30.47 Ω/sq as well as the lowest roughness value of 2.3 nm. The best condition used for the AIZO film deposited on PET substrate shows unprecedentedly low sheet resistance of only 32.63 Ω/sq which opens up enormous possibility for flexible electronics.

We breathe in a world where growing electronic wastages are a serious threat to our ecosystem, and therefore biodegradable devices are more in demand. We have unprecedentedly demonstrated broad-ban...

Bi2S3 nanoparticles (NPs) decorated ZnO nanorods' (NRs') heterostructures on glass substrate were prepared by varying the number of Bi2S3 coatings by aqueous chemical growth and SILAR techniques and their ultraviolet sensing properties were investigated. X-ray diffraction and high resolution transmission electron microscopy results confirm phase purity of the individual components and formation of the heterostructure respectively. The photoluminescence properties reveal a gradual improvement in the ultraviolet (UV) to visible emission intensity ratio up to a certain number of Bi2S3 coating due to comparatively a more decrease in the visible emission intensity. Highly enhanced UV photocurrent (∼7 times) and responsivity (∼6 times) values as compared to uncoated ZnO NRs have been noticed. Further, a very low intensity UV illumination of power density ∼21 μW/cm2 can be detected by ZnO-Bi2S3 heterostructure more efficiently as compared to pristine ZnO NRs which is attributed to an efficient charge transfer at ZnO and Bi2S3 interface.

A dipeptide-appended naphthalenediimide (NDI) is self-assembled in an aqueous phosphate buffer medium of pH 7.5 to form nanovesicular structures. Interestingly, these molecules are assembled to for...

Until now only n-type transparent conducting films (TCFs) have accomplished sufficient maturity while p-type TCFs are still in infancy which limits the success of all-transparent electronics. Considerable endeavors are made till date for development of new p-type TCFs with limited success. Here, we report a highly transparent and conducting p-type thin films (∼60 nm) based on CuS-ZnS nanocomposite deposited by simple chemical bath deposition method at ∼80 °C on glass substrates using different x values (0.1, 0.35, 0.6, 0.8) where x = Cu (mol %)/(Cu+Zn) (mol%). Grazing incidence X-ray diffractometry, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and atomic force microscopy are used to evaluate the structural and microstructural characteristics of the films. The existence of ZnS phase is seen only for x ≤ 0.6 due to a preferential deposition of CuS which helps to retain a significant visible light transparency for x = 0.6 with a small drop in the conductivity value as compared to CuS. Thus the film with x = 0.6 is found to have the optimum electrical properties with resistivity, hole concentration, and mobility values of 1.03×10−3 Ω-cm, 4.16 × 1022 cm−3, and 0.15 cm2/Vs respectively as well as an optical transmission value of 83% at 550 nm. An unprecedented figure of merit value of 9.2 × 10−4 Ω−1 is obtained for the optimized film which is not reported till date to our knowledge. A p-n heterojunction is fabricated using the optimized film on n-GaN which shows a rectification ratio of 3.06 × 104 at 2 V indicating a great potential as p-type TCF for flexible transparent electronics.

Achievement of high conductivity by doping an oxide thin film while maintaining its high visible transparency remains a challenge in the field of materials science and technology. Here, we demonstrate a simple and novel technique to control compensating defects in Al doped ZnO (AZO) thin films involving a post-growth annealing process with Zn blanket. We also provide an in-depth understanding of the mechanism of achieving high conductivity. As low as 8.8 Ω/sq sheet resistance (resistivity 3.1 × 10−4 Ω cm) with 90% visible transmission value and wherefrom a figure of merit (FOM) value of 6.5 × 10−2 Ω−1 for a RF sputtered 350 nm AZO thin film can be achieved. Such very low sheet resistance has been attributed to a decrease in the number of compensating defects and lesser out diffusion of Zn in AZO. Application of the developed AZO film as conducting substrate has successfully been tested by fabricating perovskite solar cells on flexible Corning® Willow® Glass substrate. The present findings open up the possibility of enough high quality industrial-scale production of transparent conducting oxides (TCOs) bearing crucial significance from the perspective of transparent electrodes for solar cells.

In the present scenario of energy crisis, it is inevitable to focus on the low powered or self-powered devices. Multi-spectral photoresponse is an additional advantage to the above feature. We have developed an efficient self-powered photodetector with broad wavelength detection range based on heterostructures of two wide band-gap materials ZnO and ZnS. More than two orders higher responsivity and 'ON/OFF' ratio has been observed in case of heterostructure sample as compared to pristine ZnO. On the basis of the controlled experimental results, it has been established that the interfacial surface engineering, can be useful to improve the visible response and a significant photovoltaic performance under visible light illumination can be achieved. Unlike the other recent reports on self-powered UV-visible photodetector, we have achieved two order higher visible response without compromising the UV photoresponse. Unprecedented broad wavelength photodetection in self-powered mode in the present study highlights the uniqueness and advantage of an interface in a core-shell heterostructure for photodetection applications.

A transparent conducting oxide (TCO) thin film exhibits a very high electrical conductivity and high visible light transparency with considerable practical applications in solar cells and in transparent electronics. As a promising substitute to Sn-doped In2O3 (ITO), doped ZnO thin films are widely considered due to low-cost, non-toxicity and high durability against the H plasma compared with ITO. In this review, by ‘co-doping', we mean cation-cation (two iso-valent or heterovalent cations) and cation-anion (one higher valence cation and one lower valence anion) double doping in ZnO film. This article commences with a generalized description of TCOs, ITO and single-doped ZnO followed by a discussion on co-doped ZnO. We systemically present the current progress in both co-doping studies with critically summarized results to gain an overview, especially regarding the electrical properties. The cation-cation co-doping results in a wide range of carrier concentrations and resistivity values due to the competitive Zn site substitution by two different cations simultaneously. Cation-anion co-doping leads to an expected change in the carrier concentration and resistivity values with a higher mobility in general due to fewer lattice defects. Finally, the article concludes with a brief discussion on problems and challenges to be addressed in the near future.

Phosphorus (P) doped zinc oxide (ZnO) thin film has skillfully been deposited on flexible substrate using radio frequency sputtering technique at room temperature under controlled oxygen ambient to tune its point defects. P doped ZnO film shows a very high ultraviolet (UV) photosensitivity with responsivity and detectivity values of 23.5 mA/W and 1.86 × 1013 Jones respectively as compared to the values of 0.073 mA/W and 2.56 × 1010 Jones respectively for pristine ZnO. Incorporation of P dopant under controlled oxygen ambient results in a very low dark current value due to acceptor-donor compensation leading to an unprecedentedly ultra-high photo-to-dark current ratio of 2.15×105 under 350 nm illumination. A photosensitivity under repetitive flat and bending conditions has been attained. Further, photoresponse towards a low intensity UV illumination of power 29 μW/cm2 has been noted with a photo-to-dark current ratio of 3.88 × 103 indicating an excellent photodetection efficiency of the P doped ZnO film.

There is an increasing interest in harvesting photoejected electrons for highly sensitive photodetectors, by interfacial engineering rather than the classic semiconductors. However, the widely employed device structures involving a p - n junction that causes photogenerated electron-hole separation to enhance the response are usually complex with a high fabrication challenge. Here, we present TiO 2 -based highly efficient ultraviolet (UV) photodetection by achieving its nanocrystal assembled film having high surface defects. The sol-gel derived TiO 2 films have been subjected to a post-growth annealing at 500 °C in air (SA) and vacuum (SB) and one subjected to UV treatment (SC) to tune the surface defects. The UV photoresponse results show that the nanocrystal assembled UV cured TiO 2 film shows as high as 1.7 × 10 3 UV-to-visible rejection ratio and photo-to-dark current ratio of 1.2 × 10 4 under 10 V bias and 10 μW incident light power. Most interestingly, unprecedently high photo-to-dark current ratio of the order of ∼10 4 at as low as 1 V bias condition and only 10 μW incident light without device fabrication has been observed. Moreover, the films show stable response cyclibility under UV radiation. Therefore, simple UV curing improves UV photoresponse properties of TiO 2 film enormously without the need to form conventional devices and opens the pathway for high-performance, low-cost, low-power consumption UV photodetector.

The present work demonstrates ultraviolet and visible dual-band low-intensity light detection with an improved photoresponse speed by SnO2 nanorod (NR) array film coated by polyvinyl butyral (PVB). The structural purity of the SnO2 is retained after PVB coating while x-ray photoelectron spectroscopy results indicate a less chemisorbed species on the surface of the NRs. Unprecedentedly, the PVB coated SnO2 NR array film shows highly augmented photoresponsivity values of 100 mA/W (for 300 nm) & 14 mA/W (for 550 nm) as compared to the values of 6.85 & 0.78 mA/W respectively for the uncoated one operated at +2 V due to surface modification. Interestingly, the PVB coated SnO2 NR array film is able to detect lights with very low-intensities of 14 μW/cm2 (300 nm) & 42 μW/cm2 (550 nm) resulting in higher photoresponsivity values of 153 & 18 mA/W as well as detectivity values of 1.04 × 1012 & 1.25 × 1011 Jones respectively. Fascinatingly, a PVB coating on SnO2 NR improves its photoresponse speed by an order of magnitude owing to reduced surface traps.

We present here an in-depth comprehensive study on the interplay between nitrogen (N) and various point defects in ZnO nanorods (NRs) implanted with 50 keV N ions with fluences from 1 × 1014 to 1 × 1016 ions/cm2 followed by a thermal annealing at 450 °C separately in Ar, O2, and excess Zn ambiences. Detailed X-ray diffractometry results reveal that N implantation induced structural damages increase sharply beyond 1 × 1015 ions/cm2. The Raman scattering analyses are indicative of structural disorders due to various N-related defect complexes. The analyses of X-ray photoelectron spectroscopy (XPS) results validate the incorporation of N at O sublattice forming NO acceptor and NO-VZn acceptor complex in the implanted NRs. Post-implantation annealing in Ar and O2 ambiences causes only NO state, while annealing in excess Zn ambient induces an additional shallow donor (N2)O by substituting N2 at O site. The XPS, Raman scattering, photoluminescence and current-voltage measurement results combiningly illustrate that the post-implantation annealing in O2 and Ar ambiences play a key role to stabilize the N dopants in ZnO NRs via reducing oxygen vacancy and/or preserving the concentration of N-related acceptors. This study would therefore be a benchmark for understanding the role of defects in the N doping in ZnO NRs.

The point defects in ZnO nanorods (NRs) play very crucial role in its photoconductivity (PC) properties and thus it is essential to understand the sub-band gap carrier dynamics in order to have efficient ultraviolet (UV) photodetection. In order to understand the role of a dominant point defect, Zn vacancy (VZn) which is prevalent on the surface of the NRs, we employ a high temperature annealing step in air and also an excess hydration step for one set of annealed NRs, each followed by a final surface passivation step by poly-vinyl butyral (PVB). A comprehensive study on the photocurrent spectra, photocurrent transients under different sub-band gap excitations and power dependence of photocurrent of aqueous chemically grown ZnO NRs treated under various conditions have been carried out and demonstrates the superiority (extraordinarily high and fast UV response) of the point defect rich but surface passivated NRs as compared to ones with absence or less VZn defects. Further a good support on the major role...

Herein, we report a comparative mechanistic study on cation-cation (Al-Sn) and cation-anion (Al-F) co-doped nanocrystalline ZnO thin films grown on glass substrate by RF sputtering technique. Through detailed analyses of crystal structure, surface morphology, microstructure, UV-VIS-NIR transmission-reflection and electrical transport property, the inherent characteristics of the co-doped films were revealed and compared. All the nanocrystalline films retain the hexagonal wurtzite structure of ZnO and show transparency above 90% in the visible and NIR region. As opposed to expectation, Al-Sn (ATZO) co-doped film show no enhanced carrier concentration consistent with the probable formation of SnO2 clusters supported by the X-ray photoelectron spectroscopy study. Most interestingly, it has been found that Al-F (AFZO) co-doped film shows three times enhanced carrier concentration as compared to Al doped and Al-Sn co-doped films attaining a value of ∼9 × 1020 cm−3 due to the respective cation and anion substitution. The carrier relaxation time increases in AFZO while it decreases significantly for ATZO film consistent with the concurrence of the impurity scattering in the latter.

Study on the photoluminescence (PL) properties of cation or anion doped sol-gel ZnO thin films can lead to new insights into its defects. In this work, an in-depth knowledge on defect formation in phase pure Cl doped ZnO films has been acquired through comprehensive studies on their PL properties supported by the electrical and X-ray photoelectron spectroscopy (XPS) results. Here, we demonstrate an uncharacteristic enhancement in the ultraviolet (UV)/visible (VIS) peak intensity ratio from 2.7 to 9.5 with an increase in the doping content from 0–10 at% Cl, signifying a large change in the defect chemistry. Also an atypical change in the green (GE) and orange emission (OE) with a gradual decrease in the GE/OE intensity ratio as Cl dopant increases has been observed which is not reported earlier. Critical analyses of the UV and VIS PL emissions and electrical results supported by XPS data indicate that Cl occupies oxygen vacancy site forming Cl O and forms Cl interstitial defects (Cl i ) besides a small fraction of the Cl is being substituted in the O site. Therefore, we propose that Cl O and Cl i defects act as nonradiative recombination paths for the trapped electrons and holes resulting in reduced GE and OE.

We report here excellent H 2 gas response property of Co-doped ZnO nanorods (Co:ZnO NRs). Co:ZnO NRs have been synthesized by hydrothermal method by varying the Co content from 0 to 10 mol%. It is found that Co:ZnO NRs with 8 mol% of Co exhibits the highest and faster H 2 gas response ability compared to the undoped ZnO resulting in a ∼5 fold enhancement in the gas response in the presence of air at 150 °C. While the gas response value (S (%) = [(I g -I a )/I a ] × 100, where I a is the current of the sensors in the presence of air only and I g is the current in the presence of certain H 2 concentration) to 3000 ppm H 2 for undoped ZnO NRs’sensor is 11%, an unprecedented high value of 53.7% is obtained for the Co:ZnO with 8 mol% of Co. Based on the electrical current and photoluminescence results, a mechanism for the enhanced H 2 response of Co:ZnO is proposed that involves donor-related oxygen vacancies (V O ) introduced by the Co dopants in the ZnO lattice.

A peptide appended perylene bisimide (PBI)-based new hydrogel has been discovered in phosphate buffer medium having the pH ranging from 7.00 to 9.00. This peptide appended PBI-derivative shows interesting photoswitching property in the aggregated state. This gel is thoroughly characterized by UV–visible absorption and fluorescence spectroscopy, field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and rheological studies. TiO2 nanoparticles are also prepared by using a protein amino acid, glutamic acid, in water medium. The as-synthesized TiO2 nanoparticles exhibit usual photoswitching behavior. An organic–inorganic hybrid nanomaterial is prepared by incorporating the as-synthesized TiO2 nanoparticles into the fibrillar gel network of the native gel. This TiO2–PBI-based hybrid soft material shows a characteristic of nanofiber and nanoparticle combination in their nanoscale coassembled state as it is evident from the respec...

A simple process step involving controlled cooling action was successfully established for defect control in a sol–gel ZnO film. In this study, a sol–gel process was adapted to form two sets of ZnO films with two different pre-heat treatment temperatures (set A and set B), but with the same post-heat treatment temperatures subjected to three different cooling rates (0.12, 0.25 and 90 °C s−1) for each set in order to control the defect formation. The structural and surface morphological results showed that ZnO films, for both the sets, exhibited a wurtzite structure, whereas the crystallite orientations, FWHM of the (002) peak and the surface roughness, were found to vary with the cooling rate irrespective of the pre-heat treatment temperature. The films showed phenomenal changes in the photoluminescence (PL) and ultraviolet photoconductivity (PC) results. Irrespective of the set type, the rapidly cooled (90 °C s−1) films showed an improved ultraviolet-to-visible PL intensity ratio as compared to others as a result of reduced defect emission in the visible region. The dark and photo current measurement results indicated the existence of higher adsorbed O2 molecules-related trap states and an enhanced UV photoresponse in rapidly cooled films for both the sets, providing strong evidence in support of defect control. X-ray photoelectron spectroscopy results confirmed the presence of larger adsorbed O2 molecules at the strained oxygen vacancy sites in the rapidly cooled films. These results demonstrated that the post-heat treatment cooling rate could be a brilliant and easy pathway to control the defects for tuning the optical emission and ultraviolet photosensing properties of sol–gel ZnO films.

The photoluminescence (PL) of sol–gel TiO 2 thin film has been found to be largely dependent on the post-deposition processing such as annealing at 500 °C in air, vacuum and ultraviolet (UV) light curing at room temperature. A detailed analysis of room temperature PL spectra shows that the UV/VIS PL peak intensity ratio is maximum for the film which has been annealed at 500 °C in air. X-ray photoelectron spectroscopy confirms the presence of Ti 3+ type of point defects. The visible emission is deconvoluted to green and orange emissions. Analyses of the present experimental results indicate that V O and/or Ti 3+ causes the green emission and OH and/or excess O 2 adsorption on TiO 2 surface probably causes the orange emission. The time correlated single photon counting spectroscopy data of the UV PL indicates higher number defects in vacuum annealed and UV cured films as compared to the air annealed film. Correlation of the results altogether allows us to conclude that the surface defects those causing the visible emission are smaller in number in the air annealed film. The present results may be useful for tuning the relative PL intensities of UV, green and orange emissions.

In this work, sol–gel ZnO thin films were implanted with Al ions of various fluences to study their electrical transport properties as transparent conducting oxide (TCO) layers. Additionally, formation of structural defects and modifications of the optical emission properties due to implantation have been investigated extensively to correlate the resultant electrical properties. By varying the ion fluence over two orders of magnitude from 1 × 1013 to 6 × 1015 ions/cm2, interestingly the electrical transport properties have been seen to be degraded in an unexpected manner as soon as Al is implanted and beyond a certain fluence (5 × 1013 ions/cm2), the electrical properties begin to improve. For the highest fluence (6 × 1015 ions/cm2), the sheet resistance is found to be 156 Ω/sq with an average visible transmission of 82%. The figure of merit value of our Al implanted ZnO film for an Al fluence of 5 × 1015 ions/cm2 is the highest till date, which may be prospective as a TCO layer. Detailed investigation on the evolution of the electrical and photoluminescence properties with an increase in the Al ion fluence reveals that zinc vacancy type defects are formed in large number which on healing produces further higher conductivity in the films.

We report a broad-band low-intensity photodetection enriched with a good reproducibility by SnO2 thin film grown by a facile vapour-liquid-solid technique. Unprecedentedly, simple Al/SnO2/Al photoconductive device, operated at room temperature in the wavelength range from ultraviolet (300 nm) to near infra-red (800 nm) show responsivities 2.04, 0.19, 0.25 and 0.19 mA/W respectively for 300 nm, 450 nm, 550 nm & 800 nm lights indicating broad-band photodetectivity due to its sub-band gap defects. It can also detect lights with very low-intensity of 14 μW/cm2 (300 nm), 54 μW/cm2 (450 nm), 42 μW/cm2 (550 nm) & 12 μW/cm2 (800 nm) having responsivity values of 8.00, 1.02, 1.42 and 0.70 mA/W respectively. Interestingly, the defect states within the band gap causing the photosensitivity over a wide wavelength range have been proposed uniquely by a systematic successive photocurrent transient experiment using illuminations from NIR to UV region supported by the photoluminescence results. These excellent performances unambiguously demonstrate that the simple SnO2 film is promising for utilization as efficient broad-band photodetector.

In recent times, a great deal of attention has been paid to the balanced design and fabrication of core-shell heterostructures for enhanced pseudocapacitor (SC) performance. In this paper, we report the synthesis of ZnO@Co3O4 based core-shell heterostructures with controllable shell thickness for the first time by a simple low-temperature solution-based method and their detailed electrode performance as SC wherein a highly enhanced pseudocapacitance of 296 C g(-1) at a current density of 0.5 A g(-1) has been observed. Further, modifying the surface of ZnO by its sulfur analogue (i.e., by creating a ZnO/ZnS heterostructure), an improved capacitance of 317 C g(-1) at a current density of 0.5 A g(-1) for ZnO/ZnS@Co3O4 has been obtained along with a better rate performance. This is attributed to an efficient charge transfer from ZnS to ZnO. Impressively, the core-double shell heterostructure exhibits high energy density of 36 Wh kg(-1) at a power density of 204.3 W kg(-1). Even at a very high power density of 10.9 kW kg(-1), it shows an energy density of 14.7 Wh kg(-1). To the best of our knowledge, this is the first study of the electrochemical properties of ZnO/ZnS@Co3O4 heterostructure.

On the face of massively growing market of transparent optoelectronics, developing ZnO-based transparent conductive thin films as a promising substitute for indium-free transparent electrode is extremely important. However, the detailed function of the dopants, especially co-dopants acting on the electrical and optical properties of ZnO-based transparent conductive thin films is not clear yet. We present a detailed comparative investigation on the structural, electrical and optical properties of pulsed laser deposited ZnO thin films co-doped with Sn and F for the first time. An unexpected expansion in the lattice structure has been observed when Zn2+ are replaced by Sn4+ having smaller ionic radius. Electrical measurements show that there is no anticipated change in the carrier concentration with the dopant concentration. A minimum resistivity of 2.56 × 10−3 Ohm-cm with a carrier concentration of 4.41 × 1020 cm−3 has been obtained for 1 at.% each Sn–F co-doped film. Most interestingly, a significant improvement in the ultraviolet (UV)/visible (VIS) photoluminescence peak intensity in Sn doped and Sn–F co-doped films in correlation with the structural and electrical properties allows us to propose that Sn doping into ZnO lattice causes a screening of the native Zn vacancy defects. While the presence of F co-dopant induces Sn2+ to occupy the lattice sites, as evidenced from the lattice expansion, an insignificant increase in the carrier concentration as well as enhanced UV emission of the co-doped films. The results obtained in this study shed light on the development of ZnO-based transparent electrodes.

For halide perovskite solar cells (PSCs) to fulfill their vast potential for combining low-cost, high efficiency, and high throughput production they must be scaled using a truly transformative method, such as roll-to-roll processing. Bringing this reality closer to fruition, the present work demonstrates flexible perovskite solar cells with 18.1% power conversion efficiency on flexible Willow Glass substrates. We highlight the importance of the transparent conductive oxide (TCO) layers on device performance by studying various TCOs. While tin-doped indium oxide (ITO) and indium zinc oxide (IZO) based PSC devices demonstrate high photovoltaic performances, aluminum-doped zinc oxide (AZO) based devices underperformed in all device parameters. Analysis of X-ray photoemission spectroscopy data shows that the stoichiometry of the perovskite film surface changes dramatically when it is fabricated on AZO, demonstrating the importance of the substrate in perovskite film formation.

Al doped ZnO films (AZO) have been grown by pulsed laser deposition (PLD) technique using ceramic targets sintered at different temperatures in the range 800–1400 °C. The effect of target sintering temperature on the structural, optical and electrical properties of the AZO films has been investigated. The X-ray diffraction (XRD) patterns show that besides the major hexagonal wurtzite phase of ZnO, the zinc aluminate (ZnAl2O4) spinel impurity phase is present predominantly in the targets sintered at 900 °C onwards. The XRD peak intensity of the spinel phase increases as the sintering temperature increases. Although, no such impurity has been primarily appeared in the XRD pattern of the films deposited from these targets, the presence of a probable spinel phase has been sensed by the X-ray photoelectron spectroscopy (XPS) measurements. All the films show more than 90% transparency in the region 500–1400 nm. The electrical resistance of the target pellets also decreases with an increase in the sintering temperature up to 1100 °C and then increases. Similarly, the carrier concentration increases and the resistivity decreases with the sintering temperature attaining the values of 6.36 × 1020 cm−3 and 6.38 × 10−4 Ω cm respectively for the films ablated from the targets sintered at temperatures 1000 °C (AZO1000) and 1100 °C (AZO1100) beyond which both the values deteriorate. An increase in the carrier concentration value is assigned to the modification of the grain boundaries by the spinel phase. Vacuum annealing of AZO1000 film at 350 °C results in a further increase in the carrier concentration to a value of 1 × 1021 cm−3. This film has been applied as a transparent electrode without texturing for a-Si:H solar cell which shows a conversion efficiency of ∼3.93%. Our study for the first time shows that the presence of a ZnAl2O4 phase to a certain extent in AZO film rather helps to achieve higher carrier concentration.

ZnO nanorods (NRs) of diameter ~50 nm are coated with Ag@SiO2 NPs by the two-step chemical method. The structural and morphological properties of the Ag@SiO2 NPs coated ZnO NRs confirm its structural purity as well as adhesion of Ag@SiO2 NPs onto the NRs׳ surface where thickness of the SiO2 coating has been changed. The photoluminescence (PL) properties of the coated NRs show that the intensity of the near band edge emission peak has been enhanced to as high as 7 times as compared to only ZnO NRs when a ~12 nm thick SiO2 shell exists around Ag core which acts as a spacer layer in between Ag and ZnO. The mechanism behind the enhancement is has been successfully explained by interpreting the PL results with a model which would further help one to understand similar PL enhancement in similar metal-semiconductor systems.

ZnO nanorods (NRs) have been decorated by Au nanoparticles (NPs) by a chemical method. The ultraviolet (UV) photoresponse of Au/ZnO NRs has been investigated. As the loading of Au NPs increases, the photocurrent as well as the photo-to-dark current ratio (gain) increases attaining a maximum gain value which is ∼15 times higher than that of the pristine ZnO NRs. Photoresponse enhancement is probably due to efficient separation of photo-generated electron-holes by an enhanced electric field and hot carrier injection over the Au localized Schottky junctions.

We present here a comprehensive study on the effect of Al ion implantation on the room temperature (RT) photoluminescence (PL) emission properties of aqueous chemically grown vertically-aligned ZnO nanorods (NRs) implanted with 100 keV Al ions of various doses varying from 1 × 1013 ions/cm2 to 1 × 1016 ions/cm2 followed by annealing at 450 °C in an inert ambient. As compared to the pristine sample, an unprecedented enhancement (1.4 times) in the ratio of the intensities of the near band edge, INBE (ultraviolet) to the defect level, IDL (visible) emissions has been observed for the ZnO NRs implanted with a 5 × 1013 ions/cm2 dose of Al ions. Though the ratio INBE/IDL is decreased with an increase in the Al dose beyond 5 × 1013 ions/cm2, it is still higher than the pristine sample up to a Al dose of 1 × 1015 ions/cm2. Finally, a 0.87 times drop in the ratio is observed for the highest dose (1 × 1016 ions/cm2) Al implanted sample. Detailed analyses of the RT PL results show that excitons bound to neutral Al donor for lower and non-radiative surface defects related recombination centers for higher doses are responsible respectively for highly enhanced and reduced PL emissions in Al implanted ZnO NRs.

Cu/ZnO nanorods (NRs) hybrids have been synthesized for various concentrations of Cu nanoparticles (NPs). X-ray diffraction patterns and X-ray photoelectron spectroscopy show the phase purity of the hybrids. A detailed study on the photoluminescence (PL) properties of Cu/ZnO NRs hybrids show that the near band edge emission (NBE) of ZnO is enhanced eight times after Cu loading over that of pristine ZnO NRs. The mechanism behind luminescence enhancement has been analyzed by the surface plasmon dispersion relations of Cu/air and Cu/ZnO systems. It has been confirmed that the enhanced emission is due to the surface plasmon resonance coupling of the NBE emission between Cu and ZnO.

P-doped ZnO one-dimensional (1D) nanorods (NRs), grown by simple hydrothermal method, show highly enhanced ultraviolet photoluminescence (UV PL) property as compared to the undoped ZnO sample. A detailed in-depth understanding on the mechanism behind the enhancement has been conducted by performing experimental analyses on power dependence of and annealing effect on the emissions, low temperature PL (LTPL), and electrical I–V characteristics of various P-doped ZnO NR samples. The doped NR samples retain hexagonal wurtzite structure and similar morphology as that of the undoped one. The UV/vis PL intensity ratio becomes 9 for as-grown sample and 22 for annealed 2% P-doped sample, which is one order higher than that of the undoped ZnO sample. Correlation of the LTPL and electrical I–V characteristics reveals that the high enhancement in the UVPL is due to recombination via shallow acceptor complex defects of PZn–2VZn type.

Though persistent photoconductivity and spectral response characteristics corresponding to sub-band gap energies of ZnO as a result of different defects are certainly problematic, study on this is quite useful in the sense that it provides information about the defects levels. A developed understanding of the energetic distributions of sub-band gap electron and hole traps in ZnO nanorods is pre-requisite for device applications and needs to be acquired. Through a study on the simple successive photocurrent transients of as-grown and annealed aqueous chemically grown ZnO nanorods, we have revealed the sub-band gap electron and hole traps responsible for their visible photoresponse. The evolutions in the room temperature photoluminescence properties of ZnO nanorods with annealing temperature have also been investigated critically to correlate the corresponding photocurrent results. As-grown samples show fewer excess O related electron trap states with energy corresponds to (Ec − 1.77 eV). A greater amount of O vacancy related hole traps, as well as fewer O interstitial related electron traps with energy corresponds to (Ec − 2.34 eV) were detected in the as-grown as compared to the annealed samples. These findings also provide general guidelines for probing sub-band gap traps, and engineering the optoelectronic properties of similar oxide semiconducting nanoparticles.

A novel technique of depositing multilayered films by introducing metal Zn layers in between Al-doped ZnO (AZO) films by using RF and DC magnetron sputtering has been proposed to enhance the electrical conductivity through mobility enhancement. The multilayered Zn/AZO films when annealed at 823 K, not only maintains high transparency in the visible-to-near infrared region but also shows very high mobility of 46 cm2/Vs which is thirteen times more than that of the AZO film and resistivity as low as 2.43 × 10−4 Ω-cm. The highest figure of merit value is 8.6 × 10−2 Ω−1 which is more than double to that of the value of AZO film suggesting that these Zn/AZO films are very promising for solar cell applications.

We have synthesized for the first time ZnO/rGO hybrids from metal zinc and GO using hydrothermal technique without adding further reducing agent. The photocatalytic property of ZnO–rGO reveals that the hybrid for 50 mg of GO has the highest activity, causing a 94% degradation of methyl orange compared to 70% by only ZnO. The consistent quenching and a gradual decrease in the decay life time of the emission at ∼500 nm as the rGO content increases indicates the interfacial charge transfer process between ZnO and rGO by the defect states responsible for green emission.

The effect of surface capping with poly-vinyl butyral (PVB) on the ultraviolet (UV) photosensing properties of ZnO nanorods (NRs) has been investigated. The PVB capped ZnO NRs show enhanced UV photocurrent and photoresponse due to surface modification as compared to the as-grown NRs. The photocurrent dependence on light intensity indicates that there is improvement in the space-charge–limited photocurrent in the capped NRs as compared to the as-grown NRs.

Different morphologies of ZnO nanostructures have been synthesized by chemical vapor deposition method by varying the growth temperature from 600 °C to 700 °C. Synthesized samples were characterized by X-ray diffractometry, field emission scanning electron microscopy and photoluminescence measurements. The growth mechanism of the dense intersecting branched tree-like ZnO nanostructures has been explained with the help of a schematic model. The liquefied petroleum gas (LPG) sensing performance by the nanostructures has been examined and it is found that the tree structure shows the highest response to LPG as compared to the other nanostructures with no or small branching. The mechanism of the enhanced gas response property in the tree-like structure has been explained with the help of a surface depletion model.