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This research work describes the phase change studies in Se85In15−xZnx thin films at various annealing temperatures. Glassy samples of Se85In15−xZnx were synthesized by the melt quenching method and thin films of thickness 400 nm were prepared by the vacuum evaporation technique on a glass/Si wafer substrate. The glass transition temperature (Tg) and the on-set crystallization temperature (Tc) of the prepared alloys were evaluated by non-isothermal differential scanning calorimetry studies. Thin films were annealed at three temperatures 330 K, 340 K, and 350 K (which are in between Tg and Tc of the synthesized samples) in a vacuum furnace for 2 h. High resolution X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature whereas the annealed films are of crystalline/polycrystalline in nature. Field emission scanning electron microscopy studies of thin films (as-deposited and crystallized) confirm the phase transformation in Se85In15−xZnx thin films. Optical band gaps were calculated from the Tauc's extrapolation procedure and were found to be enhanced with the Zn concentration and decrease with the increasing annealing temperature. Various optical parameters were evaluated for as-prepared and annealed Se85In15−xZnx thin films. The changes in optical parameters with annealing temperature were described on the basis of structural relaxation as well as changes in defect states and density of localized states during amorphous to crystalline phase transformation in Se85In15−xZnx thin films.This research work describes the phase change studies in Se85In15−xZnx thin films at various annealing temperatures. Glassy samples of Se85In15−xZnx were synthesized by the melt quenching method and thin films of thickness 400 nm were prepared by the vacuum evaporation technique on a glass/Si wafer substrate. The glass transition temperature (Tg) and the on-set crystallization temperature (Tc) of the prepared alloys were evaluated by non-isothermal differential scanning calorimetry studies. Thin films were annealed at three temperatures 330 K, 340 K, and 350 K (which are in between Tg and Tc of the synthesized samples) in a vacuum furnace for 2 h. High resolution X-ray diffraction studies demonstrate that the as-prepared films are amorphous in nature whereas the annealed films are of crystalline/polycrystalline in nature. Field emission scanning electron microscopy studies of thin films (as-deposited and crystallized) confirm the phase transformation in Se85In15−xZnx thin films. Optical band gaps were cal...

Particle feeding is used in the most important applications of radio frequency (r.f.) thermal plasmas like synthesis of nanoparticles and particle spheroidization. The study reports an in-situ investigation of radial distribution of temperature in such devices using yttrium ion emission lines under different rates of particle loading during synthesis of yttria nanoparticles. A number of interesting facts about the response of r.f. plasma to the rate of particle loading, hitherto unknown, are revealed. Observed phenomena are supported with experimental data from fast photographic experiments and actual synthesis results. The use of the Abel inversion technique together with simultaneous multi-track acquisition of emission spectra from different spatial locations using a CCD based spectrometer allowed us to extract accurate distribution of temperature inside the plasma in the presence of inherent instabilities. The temperature profiles of this type of plasma have been measured possibly for the first time while particles are being fed into the plasma. Observed changes in the temperature profiles as the particle feed rate increases are very significant. Reaction forces resulting from particle evaporation, and increased skin depth owing to the decrease in electrical conductivity in the edge region are proposed as the two different mechanisms to account for the observed changes in the temperature profile as the powder feed rate is increased. Quantitative analyses supporting the proposed mechanisms are presented.

The microstructure of the CdS/CuGaSe2 interface region in Cu-rich CuGaSe2-based polycrystalline thin film solar cells with KCN-treated absorber layers are characterized. Two recipes for the chemical bath deposition (CBD) of CdS with different bath temperatures (60 and 80 °C) are compared. Coherent Cu–Se precipitates are observed in both cases in the grains of the absorber layer. This precipitation cannot be avoided and seems to be a principal limitation for the performance of Cu-rich CuGaSe2-based thin film solar cells. There is a significant difference between both recipes concerning the interaction with the absorber layer surface. For bath temperatures of 80 °C the interaction is much stronger and Cu–S inclusions are found in the buffer layer. These may be responsible for shunts across the pn junction. Owing to the reduced interaction of the CdS deposited at 60 °C there are no Cu–S inclusions. For the 80 °C recipe the CdS/CuGaSe2 interface region consists of a continuous transition zone with low defect ...

Polarized Raman spectra were measured at room temperature from the (001)- and (112)-oriented CuInSe2 heteroepitaxial layers grown on (001)- and (111)-oriented Si substrates. The analysis of the results proved the expected orientation and good crystalline quality of the (001) layers. No special crystallographic direction was identified unambiguously on the (112) plane. Similar behavior was confirmed by infrared transmission spectroscopy. This can be explained by the existence of rotational twins, which have been observed by x-ray diffraction.

The microstructure of (112) oriented CuInSe2 heteroepitaxial layers grown with molecular beam epitaxy on (111) oriented Si wafers was investigated by transmission electron microscopy. Experimental and calculated diffraction patterns of different zone axes were compared. Extra spots are caused by rotational twins on (112) growth planes. Six twin variants rotated by ±120°, ±60° and 180° about the [221] axis were identified in the layers. The tetragonal chalcopyrite structure of CuInSe2, the crystal symmetry of the substrate and variations of the growth conditions during the growth are responsible for the formation of these rotational twins. Coherent twin boundaries as well as partly coherent boundaries of twin variants rotated by ±60° and 180° were imaged by high resolution transmission electron microscopy. The boundaries can be formed by inserting partial dislocations with Burgers vectors a/6〈111〉 into the CuInSe2 structure. This suggests that the annealing of the samples induces the annihilation of the...

Epitaxial growth of PbSe on (111)‐ and (100)‐oriented Si substrates without an intermediate buffer layer is studied. It is found that on Si(111) the orientation of the IV‐VI layer can by varied from (100) at 200 °C to (111) at 400 °C substrate temperature. On Si(100), only (100)‐oriented layers were obtained for the whole temperature range. (100)‐oriented layers with thicknesses above 0.5 μm were cracked due to thermally induced mechanical strain on cooldown to room temperature. This strain cannot be relaxed by dislocation glide in the first glide systems as it is the case for (111)‐oriented layers. The structural quality of (100)‐oriented PbSe layers on Si(100) and Si(111) is inferior compared to layers grown with an intermediate BaF2/CaF2 or CaF2 buffer layer. This implies that the covalent/ionic PbSe/Si interface seems to impede high‐quality epitaxy, contrary to the well known ionic/ionic IV‐VI/IIa‐fluoride interface.

Epitaxial superconducting YBa2Cu3O7−x (YBCO) thin films have been grown on Si(100) using CaF2 as an intermediate buffer layer. The CaF2(100) layers were grown by molecular beam epitaxy while for the YBCO layers a laser ablation process was used. Electron channeling patterns of the YBCO surface show the characteristic four‐fold symmetry for c‐axis orientation. The epitaxial relationship is (001)YBCO//(001)Si and [010]YBCO//[110]Si. This corresponds to a lattice mismatch of only 1% in the a‐b‐YBCO interface plane. The 60‐nm‐thick layers are crack free. Magnetic shielding properties of the epitaxial YBCO layers have been studied by measuring the zero temperature penetration depth λab(0) and the power law dependence of the transition temperature versus magnetic field.

Hydrogenated indium oxide (IOH) is implemented as transparent front contact in Cu(In,Ga)Se2 (CIGS) solar cells, leading to an open circuit voltage VOC enhanced by ∼20 mV as compared to reference devices with ZnO:Al (AZO) electrodes. This effect is reproducible in a wide range of contact sheet resistances corresponding to various IOH thicknesses. We present the detailed electrical characterization of glass/Mo/CIGS/CdS/intrinsic ZnO (i-ZnO)/transparent conductive oxide (TCO) with different IOH/AZO ratios in the front TCO contact in order to identify possible reasons for the enhanced VOC. Temperature and illumination intensity-dependent current-voltage measurements indicate that the dominant recombination path does not change when AZO is replaced by IOH, and it is mainly limited to recombination in the space charge region and at the junction interface of the solar cell. The main finding is that the introduction of even a 5 nm-thin IOH layer at the i-ZnO/TCO interface already results in a step-like increase i...

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se2 (CIGS) solar cells. Hydrogen doping of In2O3 thin films is achieved by injection of H2O water vapor or H2 gas during the sputter process. As-deposited amorphous In2O3:H films exhibit a high electron mobility of ∼50 cm2/Vs at room temperature. A bulk hydrogen concentration of ∼4 at. % was measured for both optimized H2O and H2-processed films, although the H2O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (VOC) of ∼20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H2O case or slightly decrease for H2. The overall power conversion efficiency is improved f...

Magnetron sputtering of fluorine-doped tin oxide (FTO) is a scalable deposition method for large-area transparent conducting films used in fenestration, photovoltaics, and other applications. The electrical conductivity of sputtered FTO is, however, lower than that of spray-pyrolized FTO because of the ion damage induced by high energy ions leading to a reduction of the crystal quality in sputtered FTO films. In this study, various ion species present during the reactive sputtering of a metallic tin target in a mixed Ar/O2/CF4 atmosphere are systematically characterized by energy and mass spectrometry, and possible ways of controlling the ion fluxes are explored. Ion energy distribution functions (IEDFs) of the negative ions F− and O− exhibit large peaks at an energy corresponding to the full target voltage. Although the applied partial pressure of CF4 is about 1/30 than that of O2, the obtained IEDFs of F− and O− have comparable peak height, which can be attributed to a higher electronegativity of F. The...

Doping the Cu(In,Ga)Se2 (CIGS) absorber layer with alkaline metals is necessary to process high efficiency solar cells. When growth of CIGS solar cells is performed on soda-lime glass (SLG), the alkaline elements naturally diffuse from the substrate into the absorber layer. On the other hand, when CIGS is grown on alkaline free substrates, the alkaline metals have to be added from another source. In the past, Na was believed to be the most important dopant of the alkaline elements, even though K was also observed to diffuse into CIGS from the SLG. Recently, the beneficial effect of a post deposition treatment with KF was pointed out and enabled the production of a 20.4% CIGS solar cell grown at low substrate temperature (

The importance of Cu for CdTe solar cell absorber doping has been increasingly recognized in recent years. Currently different models are being discussed how to understand the case of CuCd substitutional doping in polycrystalline CdTe solar cells. In this work an understanding is developed which is based on a low concentration deep acceptor doped CdTe layer (N a ~ 5 × 1014 cm 3 Ea ~ 300 meV above the valence band). Despite their non shallow nature Cu Cd acceptors are fully or at least heavily (gt;30) ionized. The low hole concentration in CdTe (~1 × 1014 cm 3) originates directly from low Cu solubility in CdTe bulk material and is not caused by partial ionization or compensation as proposed by earlier models. The three to four orders of magnitude difference between bulk acceptor concentration and average Cu concentration in polycrystalline CdTe is attributed to grain boundary segregation of Cu. Our model is derived from substrate and superstrate CdTe solar cell measurements controlled CdTe doping and quenching Hall Effect measurements of CdTe films numerical and analytical calculations and a broad literature survey. Based on these results routes to improve the conversion efficiency of CdTe solar cells are discussed. © 2013 AIP Publishing LLC.

The voltage dependence of the derivative of the capacitance to (the logarithm of) the measurement frequency is investigated. Relations describing this dependence are derived for the influence of carrier freeze out, of a defect distribution, and of a back contact barrier. The validity of these relations is investigated with numerical simulations.Considering the extraction of the defect density from capacitance–frequency measurements, the extension of existing formulas to different bias voltages leads to an improved accuracy and the possibility to investigate spatial non-uniformities while preserving a direct link between the defect level energy and the apparent defect density. This is illustrated with voltage dependent admittance measurements of thin film Cu(In,Ga)Se2-based solar cell devices.

In2S3 layers were deposited by flash evaporation technique with varying flash rates. The optical constants of layers based on Tauc–Lorentz model dielectric function were extracted from spectroscopic ellipsometry measurements. X-ray photoelectron spectroscopic investigation revealed the presence of oxygen impurity in as-deposited and air-annealed layers with traces of Na inclusion in the layer grown at high flash rate. The enhancement in crystalline arrangement of as-deposited layer after air annealing was confirmed by Raman spectroscopy. Rutherford backscattering measurements revealed the growth of off-stoichiometric layers at all flash rates. An analytical layer growth model has been proposed supporting the results obtained by various layer characterization techniques. The solar cells were prepared with flash evaporated In2S3 buffer layers and their performances were compared with CdS reference solar cell. A significant gain in short-circuit current was obtained after air annealing of the complete device at 200 °C for 20 min. A maximum conversion efficiency of 12.6% was delivered by a high flash rate In2S3 buffered cell with open-circuit voltage close to that of CdS reference cell. The improvement in device performance after air annealing treatment is explained by thermally enhanced Cu and oxygen diffusion from Cu(In,Ga)Se2 and i-ZnO to In2S3 layer, respectively.

Diamond nucleation on unscratched Si surface is great importance for its growth, and detailed understanding of this process is therefore desired for many applications. The pretreatment of the substrate surface may influence the initial growth period. In this study, diamond films have been synthesized on adamantane-coated crystalline silicon {100} substrate by microwave plasma chemical vapor deposition from a gaseous mixture of methane and hydrogen gases without the application of a bias voltage to the substrates. Prior to adamantane coating, the Si substrates were not pretreated such as abraded/scratched. The substrate temperature was ∼530 °C during diamond deposition. The deposited films are characterized by scanning electron microscopy, Raman spectrometry, x-ray diffraction, and x-ray photoelectron spectroscopy. These measurements provide definitive evidence for high-crystalline quality diamond film, which is synthesized on a SiC rather than clean Si substrate. Characterization through atomic force micr...

Cu(In,Ga)Se2 (CIGS) thin-film solar cells with InxSy buffer layers deposited by physical vapor deposition yield efficiencies of up to 14.8%. For substrate temperatures during the InxSy deposition ranging from 23to200°C, air annealing of the completed solar cells leads to an improvement of the photovoltaic performance. However, at substrate temperatures of 300°C, the efficiencies are practically zero, and air annealing does not improve this value. To understand the effects of substrate temperature and air annealing on the CIGS/InxSy interfaces of the solar cells, these interfaces have been studied by means of bright-field and high-resolution transmission electron microscopy, selected-area electron diffraction (SAED), and energy-dispersive x-ray spectrometry (EDX). It is shown that air annealing leads to a substantial Cu depletion on the CIGS side of the CIGS/InxSy interface, probably inducing the formation of a compositionally graded interface between the buffer and CIGS. For the 300°C sample, CuIn5S8 form...

Incorporation of a small amount of sodium into Cu(In,Ga)Se2 (CIGS) absorbers for thin-film solar cells is well known to enhance conversion efficiencies. Usually, Na is added in a way such that it is present during CIGS growth and therewith influences the growth kinetics. We have used post-deposition Na in-diffusion into as-grown, Na-free absorbers and observed typical efficiency improvements. This suggests that in general the main positive Na effect originates from changes in the electronic absorber properties rather than from modification of CIGS growth kinetics. At low substrate temperatures, Na impedes CIGS phase formation. This may explain why absorbers grown at substrate temperatures below 450°C in the presence of Na yield inferior cells compared with post-deposition-treated CIGS. We have developed post-deposition Na incorporation for the processing of flexible CIGS solar cells on polyimide substrates. A conversion efficiency of 14.1% under AM1.5 standard test conditions was independently measured. T...

Microstructural and chemical properties of the interfaces between Cu(In,Ga)Se2 (CIGS) and In2S3 layers in dependence on the In2S3 deposition temperature and Na concentration were investigated. The In2S3 layers were deposited by atomic layer deposition on CIGS layers at substrate temperatures ranging from 140°C to 240°C. Interfaces were investigated by means of scanning electron microscopy, bright-field and high-resolution transmission electron microscopy, electron diffraction, and energy-dispersive x-ray spectrometry. An orientation relationship between CIGS {112) and In2S3 {103) planes was found for the sample deposited at 210°C, whereas no orientation relationship was detected for the 240°C sample. Cu diffusion from CIGS into In2S3 was detected, as well as Cu depletion and In enrichment on the CIGS side of the interface. All three effects are enhanced with increasing deposition temperature. These results indicate the formation of a buried junction in the CIGS layer. In addition, a Na-free solar cell was...

The propagation and attenuation characteristics of electromagnetic waves through a waveguide filled with moving isotropic lossy homogeneous (TEmn modes), as well as inhomogeneous (TEm0 modes) plasma for the appropriate modes, have been theoretically studied. The expressions for the propagation and attenuation constants for TE and TM modes are found to be the same and dependent on waveguide dimension, plasma parameters, and drift velocity. The propagation characteristics near the waveguide walls are seen to be similar to the free‐space waveguide. For special cases, the effect of the inhomogeneity of the plasma medium has also been discussed. The power flow and field components existing in waveguides are also discussed in brief.