Back Material Research Articles

Electrochemical synthesis of cu-doped znte films as back contacts to cdte solar cells

Electrochemical deposition of Cu-doped ZnTe films was investigated as a back contact material for CdTe solar cells. The deposition system consisted of a potentiostat, a substrate (cathode), a Pt counter electrode, and an Ag/AgCl reference electrode. Experimental conditions were pH=2.5∽4, deposition temperature=70 ∽80°C, electrolyte concentration=0.02 M Zn2, 10-4 M TeO2, and deposition potential (Va) = -0.85 ∽ -1.0 V vs Ag/AgCl A cyclic voltammogram obtained from an ITO substrate showed a ZnTe reduction peak at Va = -0 7 ∽ -0 9 V A film obtained at pH=2.5, Va=-0.975 V showed the strongest ZnTe X-ray diffraction peak, but its surface morphology was not as smooth as the films made under the condition of pH=3∽4, Va=-0.950V. Triethanolamine did not form a complex with cu2 in acidic solution as needed for uniform Cu-doping, but oxalate anion and 1,10-phenanthrolme did at pH=2∽3. The efficiency of CdTe solar cells increased from 3.4% to 7.1% when Cu-doped ZnTe film was used as the back contact.

Effect of surface treatment and back contact material on field emission from tetrahedral amorphous carbon

The location of the barrier for electron field emission from diamond-like carbon is identified by subjecting tetrahedral amorphous carbon (ta-C) films to H 2 , O 2 and Ar plasma treatments to change their chemical termination and etch off any surface layers, and to deposit ta-C on substrates of different work function. Emission thresholds and current densities for undoped ta-C are found to be greatly increased by the plasma etching, due to an increase in emission site density, whereas little dependence was found on the work function of the back contact.

Field Emission from Carbon Films Deposited by VHF CVD on Different Substrates

ABSTRACTAs previously demonstrated, non-diamond carbon (NDC) films deposited at low temperatures 200-300 °C on silicon tips reduced the threshold of field emission. In this paper we will present the results of the study of field emission from flat NDC films prepared by VHF CVD. Emission measurements were performed in a diode configuration at approximately 10−10 Torr. NDC films were deposited on ceramic and on c-Si substrates sputter coated with layers of Ti, Cu, Ni and Pt. The back contact material influences the emission characteristics but not as a direct correlation to work function. A model of field emission from metal-NDC film structures will be discussed.

Field Emission From Tetrahedrally Bonded Amorphous Carbon as a Function of Surface Treatment and Contact Material

ABSTRACTIn order to test whether field emission from tetrahedrally bonded amorphous (ta-C) is affected by the back contact material we have carried out a series of emission experiments on Filtered Cathodic Vacuum Arc (FCVA) produced ta-C films. The measurements were made on identical films of approximately 25 nm thickness which have been grown simultaneously on various substrates of different work function. For these experiments the substrates used were p-type c-Si, n-type c-Si, SnO2, tungsten, gold, lead, aluminium, molybdenum, chromium and titanium. Threshold fields for emission were generally in the range of 5–15 V/micron and showed no direct dependence on back contact material work function. Films grown on Ti and W however had much higher threshold fields in the range 30–35 V/micron and this is thought to be associated with the native oxide which was present between the back contact and the ta-C film. As grown ta-C is also known to have a 1–2 nm thick sp2 rich layer on its surface and this layer may also have some effect on field emission. The layer was etched in either an O2 or H2 plasma and both etched surfaces led to improved emission efficiency.

A Coupled Heat and Water Flow Apparatus

Abstract To study the performance of a compacted buffer material under thermal and isothermal conditions, a coupled heat and water flow apparatus is designed and presented. In the preliminary design, a one-dimensional flow of heat and water was not achieved. However, control of temperature gradient, existence of one-dimensional flow, and uniformity of temperature and volumetric water content distributions at any cross section within the specimen are achieved in the modified design. Experimental results have shown that the temperature stabilizes very rapidly after a period of approximately 0.107 days. The moisture moves away from the hot end along the longitudinal direction of the specimen due to imposed thermal gradient. The time required for moisture to stabilize is in order of days.

Experimental determination of wall correction factors. Part II: NACP and Markus plane-parallel ionization chambers

For pt.I see ibid., vol.35, p.835-46 (1990). The formalism to derive the absorbed dose to water from ionization chamber measurements in a phantom includes several wall correction factors, katt, km and pwall, that depend on the shape, size and composition of the ionization chamber. Wall correction factors have been measured for a number of NACP and PTW/Markus chambers. Significant deviations from calculated values occur due to uncertainties in the contribution to the total ionization from the different materials of these inhomogeneous ionization chambers. Experimental values of pwall larger than one have been obtained for the NACP chamber indicating that the side and back wall material of this chamber reduce the ionization compared with the situation where all electrons originate from the water phantom.

Design considerations of gas permeable lenses

Introduction The design of rigid contact lenses has received mucla attention over the last forty years firstly with PMMA corneal lenses and more recently with gas permeable lenses. The design of rigid gas permeable lenses involves a number of factors some of which differ to those relating to PMMA. As such further research is required to determine the properties of gas permeable materials to allow their oxygen transmission property to be maximized: The purpose of this paper is to review lens design with respect to the shape of the human cornea to highlight additional properties of gas permeable materials which in turn influence lens design. Practitioners are faced with a number of factors when designing lenses and these can be grouped in respect to four main categories. 1. Back surface 2. Front surface 3. Thickness profile 4. Material choice The two main factors to be discussed in this paper are back surface design and material choice and their influence on front surface design and thickness profile will be assessed in respect to optimizing both the physiological and the optical properties of lenses.

Back injuries in industry: a retrospective study. II. Injury factors.

To evaluate the impact of back injury on industry, the authors conducted an extensive retrospective analysis of injuries among hourly employees of The Boeing Company, the largest industrial manufacturer in western Washington. The Boeing Company provided injury information on 31,200 employees for a 15-month period from July 1, 1979 to September 30, 1980. From this information, we analyzed 4,645 injury claims filed as of February 28, 1981 by 3,958 different employees. There were 900 back injuries in this group. Claims were categorized according to total incurred cost (TIC), made up of the medical costs and indemnity costs. High-cost claims were defined as those with a TIC greater than $10,000, and low-cost claims were those with a TIC less than $10,000. Among 857 claimants with 900 back injuries, lifting or material handling was much more commonly considered the cause of injury than accidents such as slips or falls. Accidents, however, had a much greater tendency to result in an expensive claim. The authors could not make reliable conclusions regarding injuries and 32 job skill classifications. The rate of injury did not vary according to day of the week or month, but a significantly higher rate of high-cost back injuries was noted on the day shift than on the evening or night shifts.

Drainage performance of geotextiles

It should be noted that the drainage conditions and mechanisms are somewhat different when geotextiles are used as back fill material behind retaining walls. One of the major differences is that the soil installed by the geotextile may not necessaroly be saturated. Generally, the drainage performance of geotextiles can be evaluated by examining combined behavior of geotextiles, soil particles and water. However, in addition to the above materials, in investigating the drainage performance of geotextiles as back fill material behind retaining walls, the effect of air should be taken into account. Therefore, this study has concentrated on investigating the effect of drainage performance of an initially dry geotextile. A further long-term test was carried out primarily to examine the mechanism and development of self-induced filters, which is believed to determine the drainage performance of the geotextile.

Retroreflective Photometry for Screen Efficiency Evaluation

An analytical treatment is given which shows that the peak luminance gain and lobe width of a back or front projection screen material can be used as coordinates on a graph to determine the transmission or reflection efficiency. The analysis assumes that the angular distribution of the gain can be expressed as a power of a cosine function. Also, a screen photometer is described which is based upon the adaptation of a spectrometer to measure screens having retroreflective characteristics. The photometer is capable of measuring luminance on the retroreflective axis and out to 15 degrees on either side of the incident beam. Screen samples, 2.54 cm sq, can be oriented through angles of +/-30 degrees to the incident beam and luminances from 1 ft-L to 10,000 f t-L (from about 3.5 cd/m(2) to 35,000 cd/m(2)) can be handled. The instrument has three modes of operation: visual, photoelectric, and photographic. A graph is presented illustrating the application of the analytical technique to provide a rapid performance evaluation and comparison of screen efficiencies.