Transparent conductive oxides are appealing materials for optoelectronic and plasmonic applications as, amongst other advantages, their properties can be modulated by engineering their defects. Optimisation of this adjustment is, however, a complex design problem. This work examined the modification of the carrier transport properties of sputtered tin-doped indium oxide (ITO) via laser annealing in reactive environments. We relate the optical modifications to the structural, compositional, and electronic properties to elucidate the precise mechanisms behind the reactive laser annealing (ReLA) process. For sufficiently high laser fluence, we reveal an ambient-dependent and purely compositional modulation of the carrier concentration of ITO thin films. Hereby, we demonstrate that ReLA utilises the precise energy delivery of photonic processing to enhance the carrier mobility and finely tune the carrier concentration without significantly affecting the crystal structure. Exploitation of this phenomena may enable one to selectively engineer the optoelectronic properties of ITO, promising an alternative to the exploration of new materials for optoelectronic and photonic applications.

The mechanisms governing the modification of the optoelectronic properties of low carrier concentration indium tin oxide (ITO) during reactive laser annealing (ReLaA) are investigated. ReLA combines the advantages of reactive ambient thermal annealing and laser annealing; utilizing laser processing of room-temperature sputtered ITO thin films in pressurized reactive environments to probe the films’ crystal structure and defect composition. Advanced ellipsometric modelling (considering depth-inhomogeneity and intra- and inter-grain carrier transport), cross-sectional transmission electron microscopy, and X-ray photoelectron spectroscopy revealed ReLA-induced depth-dependent compositional and structural modifications that tuned the carrier concentration ((0.3 − 1.27) × 1020 cm−3) and epsilon-near-zero domain ( 3.07 − 11.7 μ m ) across a wider range than previously reported.

Growth of polycrystalline CdMnTe ternary compound thin films has been carried out using cathodic electrodeposition technique at different cathodic potentials. The range of the cathodic potentials used in this work has been chosen according to the cyclic voltammogram results. The CdMnTe thin films were electroplated from electrolyte containing CdSO 4 , TeO 2 and MnSO 4 in an acidic aqueous medium. Glass/fluorine-doped tin oxide (FTO) substrates have been used to electrodeposit the semiconductor layers. The structural, compositional, morphological, optical and electrical properties of the CdMnTe thin films were studied using X-ray diffraction (XRD), Sputtered neutral-mass spectroscopy (SNMS), Scanning electron microscopy (SEM), UV–Vis spectroscopy and Photo-electro-chemical (PEC) cell measurements respectively. The primarily grown as-deposited (AD) layers went through two different post-growth surface treatment conditions- heat-treated in air in the presence of CdCl 2 (CCT) and heat-treated in air in the presence of GaCl 3 (GCT). Results from the XRD indicated the polycrystalline nature of the electrodeposited films. The electroplated films have cubic crystal structures and the preferred orientation was found to be along the (111) plane of CdMnTe. Inclusion of Mn has been qualitatively observed using SNMS measurement. The optical energy bandgaps of the thin films were found to be varying between ~ 1.90 and ~ 2.20 eV. Though all the layers after post-treatment showed p-type electrical conduction, both p and n-type conductivity were obtained at different cathodic potentials for as-deposited materials. Comparison of the deposited layers to other electrodeposited ternary compounds has also been discussed.

As the library of potential materials with plasmonic behavior in the infrared (IR) grows, we must carefully assess their suitability for nanophotonic applications. This assessment relies on knowledge of the materials' optical constants, best determined via spectroscopic ellipsometry (SE). Transparent conductive oxides are great candidates for IR plasmonics due to their low carrier concentration (compared to noble metals) and the ability to tailor their carrier concentration by manipulating the defect composition. When the carrier concentration becomes low enough, phonon and defect states become the dominant mechanisms of absorption in the IR spectral range, leading to near-IR (NIR) tailing effects. These NIR tailing effects can be misinterpreted for free carrier absorption, rendering NIR-visible-ultraviolet-SE (NIR-VIS-UV-SE) incapable of reliably extracting the carrier transport properties. In this work, we report the limitations of NIR-VIS-UV and IR-SE (in terms of carrier concentration) by investigating the transport mechanisms of indium tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behavior, grain size, presence of a substrate, film thickness, and measurement noise. Finally, we demonstrate the importance of identifying the IR optical constants directly via IR-SE (rather than by extrapolation from NIR-VIS-UV-SE) by means of comparing specific figures of merits (Faraday and Joule numbers), deemed useful indicators for plasmonic performance.

Cadmium sulphide (CdS) thin-films have been electrodeposited using two electrode system to be used as the hole back diffusion barrier (hbdb) layer for graded bandgap solar cells with p-type windows. Cadmium acetate dihydrate [Cd(CH 3 COO) 2 ·2H 2 O] and ammonium thiosulphate [(NH 4 ) 2 S 2 O 3 ] have been used as the cadmium (Cd) and sulphur (S) precursors respectively. In this work, CdS layers have been grown on glass/FTO (fluorine doped tin oxide) substrates at cathodic potentials ranging from 1300 to 1460 mV in order to find the best growth voltage. N-type conductivity is observed for all the layers and band-gap ranged between ~ 2.36 and ~ 2.40 eV for as-deposited layers and ~ 2.31 and ~ 2.36 eV for air-annealed layers. X-ray diffraction (XRD) analysis revealed cubic/hexagonal mixed crystallinity for the as-grown layers which indicates a tendency of transiting towards hexagonal structure upon annealing. Compositional and morphological characteristics of the layers have been investigated with energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) respectively.

An organic solar cell based on poly (3-hexathiophine-2,5-diyl) and [6,6]-phenyl C61 butyric acid methyl ester has been subjected to all layers treatment and was investigated for combined effects of the these layers on device performance. These treatment included optimization of active layer morphology and thickness and improving the structure of the hole and electron transport layers, as well as subjecting the full device to optimum post deposition thermal treatment. Such a device has shown an increase in the optical absorption intensity in the near infrared region compared to the reference device, which is thought to be advantageous for producing high current density. The increase in the current density has also been correlated with light trapping within the active layer and the possibility of the occurrence of total internal reflection, which was explained using total internal reflection spectroscopic ellipsometry measurements. The current density-voltage characteristics have been measured in dark and under illumination. Power conversion efficiency as high as 7% has been achieved correlated with a fill factor of 71%.

We report the low temperature (T < 70 degrees C) fabrication of ZnO thin films (similar to 140 nm) with Hall mobility of up to 17.3 cm(2) V-1 s(-1) making them suitable for thin film transistor (TFT) applications. The films were deposited by rf magnetron sputtering at T < 70 degrees C and subsequently laser processed in ambient temperature in order to modify the Hall mobility and carrier concentration. Medium-to-low energy laser radiation densities and a high number of pulses were used to avoid damaging the films. Laser annealing of the films after aging in the lab under 25%-35% relative humidity and at an average illuminance of 120 lux resulted in an overall higher mobility and relatively low carrier concentration in comparison to the non-aged films that were laser processed immediately after deposition. A maximum overall measured Hall mobility of 17.3 cm(2) V-1 s(-1) at a carrier density of 2.3 x 10(18) cm(-3) was measured from a 1 G Omega as deposited and aged film after the laser treatment. We suggest that the aging of non-processed films reduces structural defects mainly at grain boundaries by air species chemisorption, with concomitant increase in thermal conductivity so that laser processing can have an enhancing effect. Such a processing combination can act synergistically and produce suitable active layers for TFT applications with low temperature processing requirements.

Organic solar cells based on P3HT:PCBM bulk heterojunction were prepared and subjected to post annealing at different temperatures (100, 120, 140, 160 and 180 °C). SEM, AFM as well as optical images have revealed that post deposition heat treatment has induced significant phase segregation between P3HT and PCBM which were found to result in growth of PCBM clusters on the films surface. The P3HT:PCBM absorption spectra were found to be blue shifted by 7 nm in films subjected to heat treatment at 160 °C and 180 °C. XRD data show a single diffraction peak at 2θ = 5.33 ± 0.23o for P3HT:PCBM films and was attributed to the edge-on arrangement of the (100) plane. Space charge limited conduction theory was employed to determine the charge carrier mobility; the highest obtained mobility was obtained for devices with active layers heat-treated at 140 °C. The change in the barrier height was derived from dark I–V. The variation in the metal–semiconductor contact between the Al electrode and P3HT:PCBM active layer were addressed and the barrier height has increased to form hole blocking contact and the ideality factor has decreased implying a decrease in the recombination rate. A direct relation between Fermi level, Vbi, and Voc was studied. Efficient device performance was ascribed to P3HT:PCBM layers which were subjected to post deposition heat treatment at 140 °C with PCE = 5.5 %, FF = 65.6 %, Jsc = 12.9 mA cm−2 and Voc = 0.65 V.

The effect of different solvents on the optical, structural, morphology and solar cell performance of P3HT:PCBM based devices were carried out using UV-visible absorption spectroscopy, XRD, AFM, SEM, electrical conductivity as well as current density-voltage (J-V) measurements in dark and under illumination. Chloroform (CF), chlorobenzene (CB), di-chlorobenzene (DCB), and their mixtures (DCB:CB, DCB:CF and CF:CB) in the ratio 1:1 were used as solvents to produce active layers of P3HT:PCBM heterojunctions. UV-visible absorption spectra have demonstrated different absorption intensities subject to the used solvents as well as a decrease in the optical bandgap from around 1.9eV to 1.8eV. AFM and SEM images gave an indication on the films’ morphological properties, which have exhibited different topographies due to the used solvent. The electrical conductivity as well as the dark J-V characteristics were analysed using Richardson-Schottky model as well as space charge limited conduction theory to evaluate the...

We have observed for the first time a subtle chemical change in the oxidation state of Zn at the interface between a ZnO thin film and a glass substrate using gas cluster ion beam (GCIB) depth‐profiling. A combination of monoatomic and gas clusters was used for etching, allowing the removal of the surface rapidly using the monoatomic ion beam yet still yield a less damaged surface by removing the damaged layer using the argon GCIB as a final step. With this combined method, the depth‐profile shows the transition of Zn from oxide to metal at the interface, which the monoatomic ion source if used alone would damage. This data indicates that the initial layers of the film did not undergo as much oxidation during the deposition compared with the rest of the film; therefore, metallic zinc resulted at the interface. We also examined the ZnO thin film under a range of conditions of argon ion profiling from monoatomic to cluster ions to study the most efficient method for depth‐profiling of multiple layers of inorganic materials. The monoatomic ion beam does not show the transition phenomena at the interface, which was observed in cluster depth‐profiling, probably because of atomic mixing effects. This suggests that care be taken in selection of etch parameters when studying interfaces. We recommend the combination of monoatomic sputtering followed by GCIB etching as the most efficient method for looking at interfaces of inorganic thin layers from the point of view of time taken and minimising damage at interface. Copyright © 2016 John Wiley & Sons, Ltd.

High quality transparent conductive oxides (TCOs) often require a high thermal budget fabrication process. In this study, Excimer Laser Annealing (ELA) at a wavelength of 248 nm has been explored as a processing mechanism to facilitate low thermal budget fabrication of high quality aluminium doped zinc oxide (AZO) thin films. 180 nm thick AZO films were prepared by radio frequency magnetron sputtering at room temperature on fused silica substrates. The effects of the applied RF power and the sputtering pressure on the outcome of ELA at different laser energy densities and number of pulses have been investigated. AZO films deposited with no intentional heating at 180 W, and at 2 mTorr of 0.2% oxygen in argon were selected as the optimum as-deposited films in this work, with a resistivity of 1×10−3 Ω.cm, and an average visible transmission of 85%. ELA was found to result in noticeably reduced resistivity of 5×10−4 Ω.cm, and enhancing the average visible transmission to 90% when AZO is processed with 5 pulses at 125 mJ/cm2. Therefore, the combination of RF magnetron sputtering and ELA, both low thermal budget and scalable techniques, can provide a viable fabrication route of high quality AZO films for use as transparent electrodes.

Nano-structuring of metals is one of the greatest challenges for the future of plasmonic and photonic devices. Such a technological challenge calls for the development of ultra-fast, high-throughput and low-cost fabrication techniques. Laser processing, accounts for the aforementioned properties, representing an unrivalled tool towards the anticipated arrival of modules based in metallic nanostructures, with an extra advantage: the ease of scalability. In the present work we take advantage of the ability to tune the laser wavelength to either match the absorption spectral profile of the metal or to be resonant with the plasma oscillation frequency, and demonstrate the utilization of different optical absorption mechanisms that are size-selective and enable the fabrication of pre-determined patterns of metal nanostructures. Thus, we overcome the greatest challenge of Laser Induced Self Assembly by combining simultaneously large-scale character with atomic-scale precision. The proposed process can serve as a platform that will stimulate further progress towards the engineering of plasmonic devices.

The effects of metal chlorides such as LiCl, NaCl, CdCl2 and CuCl2 on optical transmittance, electrical conductivity as well as morphology of PEDOT:PSS films have been investigated. Transmittance spectra of spun PEDOT: PSS layers were improved by more than 6% to a maximum of 94% in LiCl doped PEDOT: PSS film. The surface of the PEDOT: PSS films has exhibited higher roughness associated with an increase in the electrical conductivity after doping with metal salts. The improvement in the physical properties of PEDOT: PSS as the hole transport layer proved to be key factors towards enhancing the P3HT:PCBM bulk heterojunction (BHJ) solar cells. These improvements include significantly improved power conversion efficiency with values as high as 6.82% associated with high fill factor (61%) and larger short circuit current density (similar to 18 mA cm(-2)). (C) 2015 Elsevier B.V. All rights reserved.