MOCVD of Cd(1-x)Zn(x)S/CdTe PV cells using an ultra-thin absorber layer (original) (raw)
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Effect of window layer composition in Cd 1− x Zn x S/CdTe solar cells
Progress in Photovoltaics: Research and Applications, 2014
To improve CdS/CdTe cell/module efficiencies, CdS window layer thinning is commonly applied despite the risk of increased pin-hole defects and shunting. An alternative approach is to widen the band gap of the window layer (2.42 eV for CdS) via alloying, for example, by forming compositions of Cd 1Àx Zn x S. In this study, the performance of Cd 1Àx Zn x S/CdTe thin-film solar cells has been studied as a function of x (from x = 0 to 0.9), widening the window layer band gap up to and over 3.4 eV. Optimum Cd 1Àx Zn x S compositions were clearly identified to be around x = 0.7, and limitations to the achievable photocurrent and conversion efficiencies have been addressed.
Optimisation of CdTe(1-X)SeX and MgXZn(1-X)O layers for CdTe PV devices
2020
This thesis presents a study on the optimisation of CdTe(1-X)SeX and MZO layers for CdTe PV applications. The first part of this work focused on the formation of the CdTe(1-X)SeX layers using CdSe layer and its impact on solar cell performance. Initially the incorporation of CdSe layer into conventional CdS/CdTe devices was investigated. This approach was found to be detrimental to all device parameters particularly JSC due to the formation of a CdS(1-X)SeX phase at the CdTe/CdSe/CdS interface. This phase increased the amount of parasitic absorption observed at short wavelength, reduced PV performance, and resulted in excessive void formation at the CdTe device interface. Replacement of CdS with SnO2 as the junction partner layer was found to increase the device photo response at both short and long wavelength due to removal of the CdS and efficient formation of the CdTe(1-X)SeX phase. This resulted in increased device performance of > 13% with notably high JSC values of > 29 ...
Effect of Zn Doping in CdS Thin Films on Structural, Morphological and Optical Characterization
IOSR Journal of Applied Physics, 2017
In this particular experiment we employ Chemical Bath deposition Technique. Initially the bath parameters such as temperature, pH of the precursors, molarity of the solutions, deposition time were optimized for synthesis of CdS thin films. Using above optimized parameters, we prepare Cd 1-x Zn x S thin films for the study of effect of Zn concentration on various properties of the films. The structural, Morphological and optical characterization were investigated. The XRD spectra of the Cd 1-x Zn x S films exhibit the hexagonal crystal structure with preferential orientations at (100), (002), (101), (203), (102), (110), (200) and (004) planes. The planes (101), (002), (100) exhibited the wurtzite (hexagonal type) structure. XRD pattern shows increase in half width at full maximum with Zn content. SEM micrograph shows the porous fibrous network consisting of regularly arranged matrix over which regular shaped fine particles systematically distributed. The effect of Zn concentration in Cd 1-x Zn x S thin films clearly understood from the improvement in the microstructure of the surface morphology. The optical spectra show that absorption was found decreased with Zn content of the Cd 1x Zn x S.The absorption spectra shows the significant blue shifting of absorption edge (approximately from 450-325 nm). The optical transmittance was found maximum in the visible region (450-800 nm) and increased on increasing the Zn concentration. The x=0.2 composition having maximum transmittance 78% show the maximum 3.9 eV optical band gap which may be high enough for solar cell applications.
Materials issues in very thin film CdTe for photovoltaics
Thin Solid Films, 2005
A study is made of extremely thin absorber layers of CdTe deposited onto planar substrates in order to characterise their properties. Metal organic chemical vapour deposition (MOCVD) was used to deposit the CdS and CdTe films under controlled conditions of substrate temperature and VI/II organometallic ratio. In situ laser reflectance was used to monitor the thickness of the films and also the roughening from loss of reflected intensity. The roughness of the final structure was measured with atomic force microscopy (AFM) and compared with that of both indium tin oxide (ITO)/glass substrates and CdS deposited on them. Absorber layer thicknesses of between 50 and 500 nm were deposited, the thicker layers being grown in two stages, with a highly As doped cap layer to act as a contact. A degradation of the currentvoltage characteristics was observed from good rectification at 500 nm thick absorbers to an ohmic characteristic at 100 nm thickness. This could not be simply explained by the non-coalescence of grains, based on the AFM results, but attributed to defects on the ITO/glass substrate. Improvements in the cleaning procedure resulted in good rectification for 100 nm absorber layer. It was demonstrated that CdTe covers non-planar CdS conformally within 50 nm. D
Zinc concentration effect on structural, optical and electrical properties of Cd1−xZnxSe thin films
Materials Research Bulletin, 2012
II-VI group semiconductors are important for many devices applications like solar cells, light emitting diodes, laser diodes, detectors, transparent conductive layers, optically controlled switches, thin film transistors, laser screens etc. Recently, chalcogenides have become of great interest due to their enhanced material hardness [1,2]. Zinc and cadmium chalcogenides are refractory, chemically corrosive (in liquid and vapor state) materials with high pressures of their own vapors at temperatures exceeding their respective melting points. This is promising for improving II-VI semiconductor based devices performance. CdSe is a very promising candidate for photoelectrochemical cells and photoconductive cells. ZnSe is very important material for luminescent and light emitting devices [3]. However, CdSe is found to undergo photocorrosion when used in photoelectrochemical cells, whereas ZnSe is reported to be more stable though less photoactive due to its wide bandgap [3-5]. To overcome this shortcoming, CdSe and ZnSe can be mixed so as to provide Cd 1Àx Zn x Se ternary alloys. To importance of these materials lies in the fact that their energy bandgaps and lattice parameter can be tailored independently which can lead to new semiconductor materials that may be suitable for accomplishing the twin tasks of increased absorption of solar spectrum and enhanced resistance towards photocorrosion [3,6,7]. CdSe is a popular material from the II-VI group semiconductor. It has attracted most attention for various applications such as thin film transistors, sensors, lasers, photoconductors, gamma ray detectors, photoelectrochemical cells [8-10]. CdSe is grown as ntype and hexagonal, cubic or mixed (hexagonal-cubic) crystal structures with direct bandgap energy of 1.74 eV at room temperature [8,11]. The resistivity values of CdSe thin films may be adjusted between 10 3 and 10 6 V cm by changing the deposition conditions and techniques [8,10,12]. ZnSe is n-type semiconducting material with wide bandgap (2.7 eV) [13]. ZnSe is grown as hexagonal, cubic or mixed (hexagonal-cubic) crystal structures. It is a suitable material for red, blue and green light emitting diodes, photovoltaic, laser screens, thin film transistors, photoelectrochemical cells, etc. [14,15]. Recently, ZnSe thin films have been used as n-type window layer for thin film heterojunction solar cells. Also, interest in ZnSe-GaAs heterojunction has increased in recent years because of possible applications in a number of high speed and optoelectronic devices. ZnSe is a promising candidate for the replacement of the toxic CdS in the buffer layer due to its wide bangap (2.7 eV) than that of CdS (2.4 eV) [16].
Numerical modeling of CdS/CdTe and CdS/CdTe/ZnTe solar cells as a function of CdTe thickness
Solar Energy Materials and Solar Cells, 2007
CdTe-based solar cells have long been of interest for terrestrial usage because of their high potential conversion efficiency (in the range of 18-24%) with low-cost manufacturability and concern over environmental effects. In order to conserve material and address environmental pollution concerns as well as to reduce carrier recombination loss throughout the absorber layer, efforts have been carried out to decrease the thickness of the CdTe absorption layer to 1 mm. As a result, to date, the experimental part of this study has realized cell efficiencies of 15.3% and 11.5% with 7 and 1.2-mm-thick CdTe layers, grown by close-spaced sublimation (195]. Since some problems remain with such thin 1 mm CdTe layers, possible methods to realize higher efficiency have been investigated using novel solar cell structures, with the help of numerical analyses tools. In the theory part of this study, numerical analysis with a 1-D simulation program named NSSP (Numerical Solar Cell Simulation Program) has been used to simulate these structures. We investigated the viability of CdTe thickness reduction to 1 mm together with the insertion of higher bandgap materials (i.e., ZnTe) at the back contacts to reduce carrier recombination loss there. The study shows potential results of the thickness reduction of CdTe absorption layer for a conventional CdS/CdTe/Cu-doped C structure with around 16% efficiency for cells below 3 mm CdTe. Decreases were found in spectral response that suggest from minority carrier recombination loss at the back contact interface. A higher band-gap material like ZnTe has been inserted to produce a back surface field (BSF) to inhibit the minority carrier loss at the back contact. An increase in the efficiency to about 20% has been found for a 1 mm-thin CdTe cell, which can be attributed to the increased BSF effect at the back contact of thinner CdTe-based cells.
Advances in Materials Physics and Chemistry, 2012
In this paper, Cd 10-x Zn x S (x = 0.1, 0.3, 0.5) films were deposited by using chemical spray pyrolysis technique, the molar concentration precursor solution was 0.15 M/L. Depositions were done at 350˚C on cleaned glass substrates. X-ray diffraction technique (XRD) studies for all the prepared film; all the films are crystalline with hexagonal structure .The optical properties of the prepared films were studied using measurements from VIS-UV-IR spectrophotometer at wavelength with the range 300-900 nm; the average transmission of the minimum doping ratio (Zn at 0.1%) was about 55% in the VIS region, it was decrease at the increasing of Zn concentration in the CdS films, The band gap of the doped CdS films was varied as 3.7, 3.8, 3.6 eV at x = 0.1, 0.3 and 0.5 respectively.
Photovoltaic devices on CdS and Zn(_x) cd(_1-x)S single crystals
1982
Equivalent Circuit and Diode Equation 3.7.3 Efficiency of Solar Cells and Fill Factor 3.7.4 Solar Radiation 3.8 Mechanisms in CdS/Cu^S and (CdZn)S/Gu2S Photovoltaic Cells References 48 CHAPTER 4-EXPERIMENTAL TECHNIQUES CHAPTER 5-4.1 Introduction 4.2 Crystal Growth 4.2.1 X-ray Powder Photography 4.3 Scanning Electron Microscopy 4.4 Reflection Electron Diffraction (RED) 4.5 Measurement of Current-Voltage Characteristics 4.6 Measurement of Spectral Response 4.7 Measurement of Junction Capacitance 4.7.1 Infrared Quenching of Photocapacitance References ANALYSIS OF CdS/Cu^S SINGLE CRYSTAL PHOTOVOLTAIC CELLS 5.1 Introduction 5.2 Structure of Polished and Etched (0001) CdS Surfaces 5.3 The Copper Sulphide Layer 5.3.1 Formation of Cu S on CdS X 5.3.2 Thickness of the Cu S Layer and Rate of Growth 5.3.3 The Phases of Copper Sulphides on CdS 5.4 Performance of As-Made CdS/Cu2S Heterojunctions as Solar Cells 5.5 Spectrcil Response of As
Electrical and optical properties of Cd1−xZnxS (0x0.18) grown by chemical bath deposition
Journal of Crystal Growth, 2004
Cd 1Àx Zn x S films with 0pxp0.18 were grown by chemical bath deposition technique on glass substrates from an aqueous solution containing cadmium and zinc sulfate, ammonia and thiourea. Microstructural features, obtained from X-ray diffraction and scanning electron microscopy (SEM) measurements, reveal a predominance of Wurtzite structure and an homogenous microstructure formed by densely microcrystallines for all the samples studied. Cd 1Àx Zn x S semiconductor was found to be resistive and of n-type. Also, the electron density decreases with increased x and the mobility reaches a maximum around x ¼ 0:12: Which means that the Cd 1Àx Zn x S films at this composition are of high crystalline quality, i.e. having reduced intrinsic defect concentrations.