Selenium Vapor Pressure Research Articles

Study on synthesis of LiGa0.3In0.7Se2 polycrystal by vapor transporting temperature oscillation method

LiGaxIn1−xSe2 is one of promising semiconductor nonlinear optical crystals for laser frequency conversion in the mid-IR spectral range. Single-phase LiGa0.3In0.7Se2 polycrystal were synthesized directly from the constituent elements by vapor transporting and temperature oscillations method. According to this method, explosions of quartz ampoule that result from selenium vapor pressure at high temperature were solved. After synthesis, structure and composition of the obtained ingot were measured. And the results manifest that high purity LiGa0.3In0.7Se2 polycrystal were successfully synthesized and intermediate impurities have not been found on the compound.

Selective crystal growth of indium selenide compounds from saturated solutions grown in a selenium vapor

Indium selenide compounds are promising materials for energy conversion, spintronic applications, and chemical sensing. However, it is difficult to grow stoichiometric indium selenide crystals due to the high equilibrium selenium vapor pressure and the complicated phase equilibrium system of indium selenide compounds. In this paper, we apply a novel and convenient crystal growth method, in which the saturated solution is grown by the application of a selenium vapor. In this method, selenium vapor at a pressure higher than the saturated vapor pressure is applied to molten indium, such that the selenium continuously dissolves into the indium solution until the solubility at the growth temperature is reached; then a slow cooling process results in crystallization. The selenium dose is matched to its solubility so that indium selenide compounds can be selectively grown just by controlling the temperature without the need to consider the chemical ratio in the solution. The pressure of the vapor is controlled during the whole growth process so that any deviation from a stoichiometric composition in the crystal can be controlled. Both InSe and In2Se3 were successfully grown using this method, and we have investigated the growth mechanism and found the growth window for each compound. This study presents a novel and convenient approach to fabricating transitional metal chalcogenides without deficiencies in the chalcogen element.

Inkjet printed CuIn(1-X)GaXSe2 thin film by controlled selenium distribution for improved power conversion efficiency in chalcopyrite solar cells

Selenium (Se) vapor pressure is a key factor during the selenization of CuIn1-XGaX (CIG) film to obtain a high-quality CuIn1-XGaXSe2 (CIGS) absorber layer. To investigate the effect of Se vapor distribution on the grain growth of inkjet printed precursor film, two geometries of graphite box (square and circular) are used. The results revealed that selenization in the round graphite box give rise to uniform surface coverage and suppressed fine-grained layer due to adequate and uniform distribution of Se vapor. In contrast, film selenized in a square graphite box exhibits high strain and low crystallinity with a thick fine-grained layer. Probable Se vapor distribution inside the graphite box based on internal geometrical constraint and its impact on crystal phase and microstructure is discussed. Finally, CIGS devices fabricated using films selenized in a round graphite box demonstrates higher power-conversion efficiency of 5.2%, owing to high light absorption and efficient carrier separation. Based on J-V and EQE results, probable losses and recombination in the devices are examined and discussed.

Enhanced external quantum efficiency from Cu2ZnSn(S,Se)4 solar cells prepared from nanoparticle inks

Cu2ZnSn(S,Se)4 (CZTSSe) thin film photovoltaic absorber layers are fabricated by selenizing Cu2ZnSnS4 (CZTS) nanoparticle thin films in a selenium rich atmosphere. The selenium vapor pressure is controlled to optimize the morphology and quality of the CZTSSe thin film. The largest grains are formed at the highest selenium vapor pressure of 226 mbar. Integrating this photovoltaic absorber layer in a conventional thin film solar cell structure yields a champion short circuit current of 37.9 mA/cm2 without an antireflection coating. This stems from an improved external quantum efficiency characteristic in the visible and near-infrared part of the solar spectrum. The physical basis of this improvement is qualitatively attributed to a substantial increase in the minority carrier diffusion length.

Microstructure Evolution During Selenization of Cu2ZnSnS4 Colloidal Nanocrystal Coatings

Annealing colloidal nanocrystal coatings in a selenium-containing environment to form polycrystalline thin films of the earth-abundant solar absorber copper zinc tin sulfoselenide (CZTSSe) is an attractive approach for making solar cells. We used a closed selenization system to investigate how coatings comprising copper zinc tin sulfide (CZTS) nanocrystals evolve into polycrystalline CZTSSe thin films and studied the effects of selenium vapor pressure, annealing temperature, and heating rate. These studies revealed two different types of microstructures and two different grain growth mechanisms depending on whether the CZTS nanocrystals are exposed to selenium vapor only or to both selenium vapor and liquid selenium. Coatings annealed in the presence of selenium vapor form a microstructure comprising micron-size CZTSSe grains on top of a nanocrystalline, carbon-rich, CZTSSe layer. The film microstructure is controlled by concurrent normal and abnormal grain growth, and the grain size distribution is bimod...

Selenization of printed Cu–In–Se alloy nanopowder layers for fabrication of CuInSe2 thin film solar cells

One of the promising low cost and non-vacuum approaches for the fabrication of semiconductor CuInSe2 and Cu(In,Ga)(S,Se)2 thin film absorbers is the printing of precursor materials followed by a sintering/selenization process. The selenization process parameters such as temperature, duration, and selenium vapor pressure strongly influence the morphology and electronic properties of the absorber film. In this study, the effect of pre-annealing in an inert atmosphere and selenization on printed mechanically synthesized CuInSe0.5 alloy nanopowder precursor films was investigated. 1–2μm thick CuInSe0.5 alloy nanopowder layers were deposited on a Mo-sputtered glass substrate by means of doctor blade coating of a nanopowder based precursor suspension. Pre-annealing was performed on a hot plate inside a nitrogen gas filled glove box. Selenization was performed in a home-made rapid thermal processing (RTP) furnace with two RTP heating zones for independent temperature control of the selenium source and the coated substrate. The temperature of the selenium source was fixed at 390–410°C during the selenization to provide a constant supply of selenium vapor. A two-step process, i.e., a pre-annealing in nitrogen atmosphere at 400°C for 30min followed by selenization at 530°C for 15min was found to result in better densification and grain growth of the CuInSe2 phase, compared to a single step selenization at 530°C for 15min. The solar cell fabricated by the two-step process had an efficiency of 5.4% and a fill factor of 52%, while the device fabricated by the single step selenization had an efficiency of 1.1% and a fill factor of 31%.

Is it Possible to Grow Thin Films of Phase Pure Kesterite Semiconductor? A ZnSe case study

ABSTRACTThe kesterite semiconductor Cu2ZnSnS(e)4 is seen as a suitable absorber layer to replace Cu(In,Ga)Se2 in thin film solar cells, if thin film photovoltaics are to be deployed on the terawatt scale. Currently the best devices, and hence the best kesterite absorber layers are grown away from stoichiometry and are zinc rich and copper poor, presumably leading to the formation of ZnS(e). However, it has been shown that secondary phases present in an absorber layer reduce device performance. If growth in Zn rich conditions seems to be mandatory, then any secondary phases formed should be grown on the surface of the absorber layer so that they may be easily removed by etching. Therefore, it is important to know how and why secondary phases form, and if possible, how to segregate them to the surface of the absorber layer.Here we show that ZnSe is formed at the initial stages of absorber formation from annealing metal stacks in selenium vapor. Further we demonstrate that the way the precursor metals are distributed on the substrate leads to different absorber layer performances in full devices. The importance of selenium vapor pressure is highlighted in respect to the order of selenisation of the metals, Zn before Cu. Additionally, the importance of selenium and tin selenide vapor pressure during annealing is reviewed with regard to avoiding a decomposition of the Cu2ZnSnSe4 to ZnSe and Cu2Se phases. Regardless of the atmosphere above the absorber, the reaction of the absorber with molybdenum appears unavoidable without the use of a passivation strategy. Counter-intuitively, it is demonstrated that for our absorber layers grown under Zn-rich conditions, removal of the ZnSe is harmful for device performance.

Growth mechanism of thermally processed Cu(In,Ga)S2 precursors for printed Cu(In,Ga)(S,Se)2 solar cells

AbstractWe investigate a process used for the selenisation of particle‐based precursors to prepare low‐cost Cu(In,Ga)(S,Se)2 (CIGS) solar cells. It is suitable for high throughput with a short optimum selenisation duration of 3–5 min and employs a rapid thermal annealing system with elemental selenium vapour. Homogeneous crack‐free Cu(In,Ga)S2 precursor films of up to 1 µm are obtained via doctor blading. The high selenium vapour pressure in the selenisation reaction chamber results in the formation of a compact Cu(In,Ga)(S,Se)2 layer on top of a carbon‐rich underlayer. In order to investigate the phase development in the film, the selenisation process was interrupted at different stages and the samples were monitored via XRD and surface‐sensitive Raman measurements. We find the formation of a polycrystalline Cu(In,Ga)Se2 phase already after 1 s at the target temperature of 550 °C. Furthermore, the effect of initial precursor thickness on solar cell parameters is discussed. Complete solar cells are prepared by conventional methods, leading to conversion efficiencies well above 8%. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

8.01% CuInGaSe2 solar cells fabricated by air-stable low-cost inks

CuInGaSe(2) (CIGS), a promising thin film solar cell material, has gained lots of attention in decades due to its high energy conversion efficiency and potential lower manufacture cost over conventional Si solar cells. As a cheaper processing method compared to vacuum-based techniques, solution-based deposition has been successfully applied to fabricate electronic devices, such as transistors and solar cells. In this paper, we reported CIGS thin film solar cells with an energy conversion efficiency reaching up to 8.01% using air-stable, low-cost inks. The newly developed inks consist of commercially available, low-cost compounds and solvents and can be processed using a variety of printing and coating techniques. More importantly, the inks can produce CIGS films free of copper selenides and amorphous carbon, two common by-products from solution-based CIGS processes. The mechanism for the transformation from metal salt precursor films to CIGS absorber thin films and the influence of selenium vapour pressure on absorber film quality and photovoltaic device performance were investigated and discussed. High-quality CIGS films with micrometer-sized crystals were obtained by using higher selenization partial pressure.

Planar microdischarge device for high-speed infrared thermography: Application of selenium-doped silicon detectors

The authors investigated a possibility to develop a technique for high-speed and high-sensitivity imaging in the infrared range of light. The corresponding study was done by applying a planar microdischarge device that was a semiconductor-gas-discharge image converter. The requirements for developing the semiconductor component of the device were formulated to enhance the high-speed performance of the device. To meet these demands, extrinsic selenium-doped silicon detectors were developed. The doping of the semiconductor with selenium was done by high-temperature diffusion of the element from the vapor phase. To find the optimal conditions for the preparation of detectors, the efficiency of doping silicon with selenium as a function of the selenium vapor pressure was studied. The operation of the microdischarge device where the developed detectors were applied was investigated. This study demonstrates that converters equipped with Se:Se detectors can provide imaging of objects heated to temperature Tmin∼200°C with a temporal resolution on the order of 10−6s and a spatial resolution of ∼5lines∕mm.

Development of photodetectors for image converters: Doping of silicon with selenium from the gas phase

High-speed recording of processes in the IR spectral range can be carried out using image converters of the “semiconductor photodetector + gas discharge gap” type. To develop photodetectors with the properties required for this purpose, the effect of the selenium vapor pressure P Se on the doping efficiency of single-crystal silicon with selenium has been studied. Selenium was introduced by diffusion in sealed quartz cells at a temperature of 1240°C in the pressure range P Se = 0.27–1.0 atm. Doped samples were studied by performing temperature measurements of the Hall effect. A heavy dependence of the concentration of the impurity centers introduced on P Se was observed. It was found that the doping effect is the same for starting crystals produced by floating zone melting and by the Czochralski method. The data obtained were used to fabricate photodetectors that can be employed in high-speed thermography with the use of the image converters under consideration.

Influence of annealing conditions on the structural quality of CuInSe 2 thin films

CuInSe 2 (CIS) films have been prepared by one-step electrodeposition technique. The effect of thermal treatment in vacuum and under selenium vapour pressure on the composition and structure of CIS electrodeposited layers has been investigated. The structure and composition of these samples have been investigated by SEM, XRD, EDX and Raman spectroscopy. It was found that recrystallization of CIS thin film occurs with segregation of Cu–Se phases onto the bottom of films and formation of CIS grains different by size and composition.

High temperature electrical conductivity in ZnSe:In and in CdSe:In under selenium vapor pressure

AbstractHigh temperature electrical conductivity (HTEC) isotherms and isobars of ZnSe:In and of CdSe:In are compared. There are differencies in In‐doping mechanisms of II–VI compounds. When HTEC isotherms and isobars of ZnSe:In and of CdSe:In, measured under metal component vapour pressure give both n‐type conductivity then differences appear in the results of measurements under the selenium vapor pressure (p). ZnSe:In isotherms in the last case are characterized by the conductivity type conversion but no such drastic change of HTEC type is observed on CdSe:In isotherms. Under the conditions of p, the activation energy of HTEC isobars for ZnSe:In is ΔE ≈ 1.3–1.6 eV and for CdSe:In is ΔE ≈ 1.2 eV. The onefold ionized substitutional In at Zn place is proposed to be compensated by native defects in ZnS:In and in CdSe:In under high p. This native defect may be onefold ionized zinc vacancy for ZnSe:In and twofold ionized cadmium vacancy for CdSe:In. Association of defects occur at lower temperatures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High temperature electrical conductivity in ZnS:Al and in CdSe:Al

High temperature electrical conductivity (HTEC) as a function of temperature and component vapour pressure has been investigated in ZnS:Al and in CdSe:Al single crystals using a two zone resistance furnace and a vacuum sealed quartz ampoule with four tungsten or graphite electrodes. The activation energies of HTEC isobars and the slope values of HTEC isotherms in the large temperature region (500–1200 °C) and in a large component vapour pressure range were determined. The region of compensation of electrons with onefold ionized substitutional Al exists up to change with the region of self-compensation of native defects at high Cd vapour pressures in HTEC isotherms of CdSe:Al. These two electroneutrality conditions were never achieved in ZnS:Al crystals under investigation. The common feature for ZnS:Al isotherms at zinc vapour pressure and for CdSe:Al isotherms at selenium vapour pressure is the existence of self-compensation of Al defects. The equilibrium constant of the association of aluminium with cadmium vacancies in CdSe:Al was determined. The increasing role of holes appears similarly at low Zn vapour pressure values in ZnS:Al and at high selenium vapour pressure values in CdSe:Al.

CIS and CIGS layers from selenized nanoparticle precursors

Advances in nanoparticle technology led to powerful low-cost thin film techniques. Together with the established selenization method, these techniques open new possibilities for low-cost solar cell production that does not require expensive vacuum deposition systems. The chemical conversion (selenization) of nanosized precursor materials into CuInSe 2 (CIS) and Cu(In,Ga)Se 2 compounds and microstructural properties of these layers have been investigated. Three categories of nanoparticles, namely metal-oxides, metal-selenides and elemental metal particles were selenized in selenium vapour. Using two different reactor designs, the influence of the selenium vapour pressure was investigated. While oxide and selenide precursors show limited sintering and chemical conversion, dense CIS layers with large grains (∼1–2 μm) were obtained with metal precursors.

Optical properties of agbise 2 thin films

Thin films of AgBiSe 2 were prepared by thermal evaporation in vacuum (10 −6 Torr). The effect of thermal annealing either in vacuum or in a selenium atmosphere on the growth characteristics and stability of the films were studied using X-ray diffraction, transmission electron microscopy and the selected area electron diffraction techniques. It was observed that the as-deposited films (300 K) were poor crystalline. The degree of crystallinity increases with increasing the temperature from 300 to 473 K. At 500 K in vacuum two-phase films with AgBiSe 2 as the major phase were formed. The optical constants of crystalline AgBiSe 2 thin films were estimated as well as the effect of heat treatments and selenium vapor pressure on these constants. The analysis of the optical absorption spectra revealed the existence of two optical transition mechanisms: allowed direct and indirect transition, with optical energy gaps E d g = 1.66 eV and E g = 0.91 eV at 300 K. These values were found to decrease with increasing annealing temperature.

Temperature-resolved photoluminescence studies of CuInSe 2

Photoluminescence (PL) studies of CuInSe 2 powders, as function of temperature, have been performed. At low temperatures the k-band, centered at hv max ≈ 0.92 eV dominates the PL intensity. Increasing the temperature leads to rapid quenching of the intensity k-band and thus the j-band with hv max ≈ 0.95 eV appears. The calculated activation energies of temperature quenching for j-band lie near 20 meV value and seems to have a tendency to increase with an increasing of selenium vapour pressure. The phonon-broadening analysis of the j-band indicates, that the radiative recombination is accompanied by the emission of 3.4 phonons with mean energy of 10.23 meV. The j-band is concluded to be associated with donor-acceptor recombination from donor level E D = 60 meV to acceptor level E A = 20 meV.

Kinetics and Diffusing Species of the High-Temperature Selenidization of Molybdenum

Abstract A molybdenum sheet was selenidized at a selenium vapor pressure of 0.40—13.3 kPa at 773—973 K by means of a sealed-tube method. X-Ray diffraction patterns and an electron probe microanalysis of the product films showed that a single layer comprising MoSe2 was formed under all of the selenidization conditions employed. All of the selenidizations obeyed a parabolic rate law and, therefore, the rate-determining step was apparently a diffusion process. The parabolic rate constant (Kp) was expressed as a function of the absolute temperature, and the selenium vapor-pressure dependence of Kp could be clearly recognized. A marker experiment indicated that selenium was the component which diffused.

Mikro-Raman-spektroskopische Charakterisierung von CuInSe2-Dünnfilm-Halbleitern / Micro Raman Spectroscopy of CuInSe2 Thin Films

Structural properties for Cu—In—Se thin-films for solar cell applications formed by electrochemical deposition at room temperature were studied using Raman-scattering. Reactions among Cu, In and Se to binary compounds and CuInSe2, respectively, were observed. It is concluded that Raman scattering spectroscopy only at low temperature conditions shows the real composition of the electrochemically deposited Cu—In—Se layer. It was also found by Raman spectroscopy that the CuInSe, phase is formed by annealing as-deposited Cu—In—Se thin films preferentially at temperatures around 400°C under selenium vapour pressure.

Method of selenizing liquid Cu-In alloy in growing CuInSe2 single crystals

Stoichiometry-controlled growth of single-crystalline CuInSe 2 has been studied using a method of selenizing liquid Cu-In alloy. X-ray diffraction study reveals that selenization temperatures above the melting point of CuInSe 2 are indispensable for the single-phase synthesis with preventing binary additional phases such as Cu 7 Se 4 and In 2 Se. The electrical properties are controllable by adjusting the initial Cu/In ratio and /or applied selenium vapor pressure during the crystal growth. The application of selenium vapor pressure around 200 Torr is effective for the reduction of imperfections in p-type crystals