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Electrochemical mechanical deposition (ECMD) is a new method that has the ability to deposit planar copper films on nonplanar substrate surfaces. The technique involves electrochemical deposition (ECD) and simultaneous sweeping of the substrate surface with a planarization pad. In this study, we investigated if there were any fundamental differences in the crystallization mechanisms of copper layers grown by the ECD and ECMD techniques. Comparing the variation of the electrical resistivity values over time for films deposited by ECD and ECMD methods and stored at around 18 °C, we found that there were only slight differences in the incubation periods of self-annealing. The activation energies for recrystallization were found to be 0.71 and 0.61 eV for layers grown by the ECD and the ECMD techniques, respectively. The major difference between the ECD and ECMD films was found in the crystalline texture, with ECD layers having a higher degree of (111) preferred orientation compared to the ECMD layers in their as-deposited form. After annealing, the situation reversed, and the ECMD layers displayed a higher (111)/(200) ratio compared to the ECD layers. Differences in texture are believed to result from the mechanical action of the pad on the ECMD copper layers which interfere with and alter the orientation of the growing grains. After high-temperature annealing, ECMD Cu layer microstructure was found to display larger grain size and more fully developed twins indicative of more complete recrystallization.

A novel electrodeposition technique is described for deposition of conductors on non-planar surfaces of substrates in a planar manner. Electrochemical Mechanical Deposition (ECMD) technique involves simultaneous electrochemical deposition and mechanical polishing of the substrate surface. Copper layers deposited by the ECMD process grow preferentially in cavities on the wafer surface yielding flat profiles and much reduced overburden thickness. ECMD technology's potential to reduce cost of interconnect fabrication and some of its enabling features are discussed in this paper.

We examined the effect of deposition of Na on Mo-coated glasses and the Na content of the substrate glass on standard production Cu(In 1− x Ga x )Se 2 (CIGS)-based solar cells fabricated by selenization of Cu-Ga-In precursor thin films. Under optimal conditions, net Na content has a larger effect on the films than does the choice of substrate glass. Device performances improved with modest amounts of added Na on borosilicate glass. Device performances on soda-lime glass were not improved by adding Na. The supply of Na appears to have been adequate from the glass itself. A peak in device performance was found as a function of integrated Na in the CIGS layer as determined by secondary ion mass spectrometry (SIMS). The Na is found primarily in the areas of decreased grain size in the selenized CIGS where Ga is also found. S, deposited with the Na does not end up in the same place as does the Na. Rather, it tends to move toward the surface and accumulate in a buried layer. This is probably due to the reaction process rather than to the microstructure. Oxygen has no apparent effect on Na behavior in the CIGS.

A systematic study was carried out to investigate the distribution of sulfur (S) in CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) absorbers which were exposed to an H2S atmosphere at elevated temperature. Results demonstrated that S diffusion into CIS layers was a strong function of the original stoichiometry of the absorber before sulfurization. Sulfur inclusion into Cu-rich CIS films was much more favorable compared to S diffusion in Cu-poor layers. The sulfur distribution profile was also strongly influenced by the micro-structure of the original CIS and CIGS layers, with sections of the films with smaller grains accommodating more S. Copyright © 2000 John Wiley & Sons, Ltd.

The group of chalcopyrite semiconductors in the Cu(In,Ga)(Se,S) 2 or CIGSS family synthesized by vacuum techniques have been successfully used in the fabrication of high efficiency thin film solar cells. This paper concentrates on a group of low cost, non-vacuum approaches that are highly promising as alternative methods of preparing chalcopyrite absorbers for thin film solar cell applications. Techniques which are based on ‘particle deposition’ fix the metal ratios in a source material containing sub-micron size particles and then transfer this fixed composition onto large area substrates. In this contribution we present data on nano-particle deposition techniques that yielded chalcopyrite absorbers for the fabrication of over 10% efficient solar cells. Mini-modules with over 7% efficiency have also been fabricated using these low cost approaches.

A novel technique was demonstrated for the growth of CuInSe 2 (CIS) thin "lms. The technique used an ink formulation containing sub-micron size particles of Cu}In alloys. A metallic precursor layer was "rst formed by coating this ink onto the substrate by spraying. The precursor "lm was then made to react with Se to form the CIS compound. The morphology of the CIS layers depended on the initial composition of the Cu}In particles as well as the post-deposition treatments. Solar cells were fabricated on CIS absorber layers prepared by this low-cost ink-coating approach and devices with a conversion e$ciency of over 10.5% were demonstrated. ( 2000 Elsevier Science B.V. All rights reserved.

A novel technique is developed for the deposition of CuInSe2 (CIS) thin films for solar cell applications. The technique uses an ink formulation that contains Cu-In metallic pigments. A precursor layer is first formed coating this ink onto the selected substrate. The precursor film is then reacted with Se to form the CIS compound. Solar cells were fabricated on CIS absorber layers prepared by this low cost ink coating approach and devices with a conversion efficiency of over 9.0% were demonstrated. © 1998 The Electrochemical Society. S1099-0062(98)08-063-8. All rights reserved.

High efficiency solar cells can be fabricated on CdTe films prepared by a wide variety of deposition techniques. Most of these methods yield CdTe layers that need to be subjected to post-deposition treatments before they can be utilized in high efficiency device fabrication. In some cases these treatments can be made an integral part of the film growth process so that a post-deposition step is not needed. This paper discusses the procedures that are commonly used in high efficiency CdTe solar cell fabrication and reports on a newly emerging technique that holds the promise of becoming a high-throughput industrial process for thin film photovoltaic module production.

CuInSe/sub 2/ (CIS) films were grown on glass and metallic foil substrates by the selenization method. Both E-beam evaporation and sputtering techniques were utilized for the preparation of Cu-In precursors and the properties of these layers were studied. Modules with 816 cm/sup 2/ aperture area yielded efficiencies of about 5% and a power output of 4 W. Smaller modules with efficiencies as high as 7.4% were also demonstrated. An efficiency of 9% was obtained for small area solar cells fabricated on flexible metallic foils. >

CuInSe2and related I-HI-VI2 compound semiconductors containing Ga and S are important photovoltaic materials with electrical and optical properties that can be tuned for optimum device performance. Polycrystalline thin films of ternary and multinary compounds from the Cu(In,Ga)(Se,S)2family have already yielded laboratory size solar cells with over 15 % efficiency. Large area photovoltaic modules with over 10% efficiency have also been demonstrated using these materials. In this contribution we present a brief review of the CuInSe2 material characteristics which are important to solar cell performance and their correlation with the processing variables. We concentrate on films obtained by the selenization technique. Selenization of Cu-In precursors is an approach that has yielded good quality CuInSe2films which have been used for the fabrication of high efficiency solar cells.

This report describes a project to develop a high efficiency thin film CuInSe{sub 2} solar cell using a low-cost process. The two-stage process involves depositing the metallic elements of Cu and In on a substrate in the form of stacked layers, and then selenizing this stacked metallic film in an atmosphere containing Se. Early research concentrated on the electrodeposition technique for depositing the Cu and In films on Mo-coated glass substrates. This resulted in small-area cells with around 10% efficiency, indicating that the technique could yield CuInSe{sub 2} films with good electrical and optical properties. The program then involved scaling up the electrodeposition/selenization technique; fixtures for large-area plating were designed and built, but poor adhesion of the CuInSe{sub 2} films to the Mo-coated substrates and the stoichiometric non-uniformities encountered in the large-area films hindered the efficiency of the devices. The latter part of the program explored a new approach to the two-stage process. An evaporation/selenization approach, where the elemental layers were evaporated onto the Mo-coated substrates for selenization. Solar cells have been produced with efficiencies approaching 11% using E-beam evaporated/selenized CuInSe{sub 2} films. 9 refs., 14 figs., 2 tabs.

This report describes a research program to develop a low-cost technique for producing Cd{sub 1-x}Zn{sub x}Te devices for cascade solar cell applications. The technique involves a two-stage process for fabricating such devices with a band gap of about 1.7 eV and a transparent contact layer of low-resistivity ZnTe. In the first stage, thin films of Cd, Zn, and Te are deposited in stacked layers as Cd{sub 1-x}An{sub x}Te. The second stage involves hearing and reacting the layers to form the compound. At first, electrodeposition was used for depositing the layers to successfully fabricate Dc{sub 1-x}Zn{sub x}Te thin-film devices. These films were also intrinsically doped with copper. For the first time, transparent ZnTe films of low resistivity were obtained in a two-stage process; preliminary solar cells using films with low Zn content were demonstrated. A second phase of the project involved growing films with higher Zn content (>15%). Such films were grown on CdS-coated substrates for fabricating devices. The effects of the solar-cell processing steps on the Cd{sub 1-x}Zn{sub x}Te and CdS/Cd{sub 1-x}Zn{sub x}Te interfaces were studied; results showed that the nature of the interface depended on the stoichiometry of the Cd{sub 1-x}Zn{sub x}Te thin film. A sharp interface was observedmore » for the CdS/CdTe structures, but the interface became highly diffused as the Zn content in the absorber layer increased above 15%. The interaction between the CdS window layer and the Cd{sub 1-x}Zn{sub x}Te absorber layer was found to result from an exchange reaction between Zn in the absorber layer and the thin CdS film. 14 refs., 10 figs.« less

Electrochemical mechanical deposition (ECMD) planarizes copper films as they are plated on patterned wafer surfaces. The technique involves electrochemical deposition (ECD) and simultaneous sweeping of the cathode surface with a pad. Pad sweeping gives rise to a mechanically induced current suppression (MICS) phenomenon if plating is performed in electrolytes containing accelerator and suppressor additives as well as Cl - ions. In this work we studied the MICS phenomenon by partially sweeping blanket wafer surfaces with a small pad and investigating effects of the bath chemistry and wafer surface derivatization on the copper growth rates at the swept and unswept regions of the surface. It was found that, at a given suppressor concentration, copper growth rate differential between the two regions was reduced with increasing accelerator concentration in the bath. Derivatization of the wafer surface in an accelerator-containing solution followed by ECMD in a suppressor-containing bath gave the largest growth differential between the swept and unswept surface portions, suggesting high planarization efficiency. Adsorption-desorption kinetics of the organic additives used in this work were obtained under ECD conditions and found to support the proposed mechanism of MICS.

A novel technique is developed for the deposition of CuInSe2 (CIS) thin films for solar cell applications. The technique uses an ink formulation that contains Cu-In metallic pigments. A precursor layer is first formed coating this ink onto the selected substrate. The precursor film is then reacted with Se to form the CIS compound. Solar cells were fabricated on CIS absorber layers prepared by this low cost ink coating approach and devices with a conversion efficiency of over 9.0% were demonstrated. © 1998 The Electrochemical Society. S1099-0062(98)08-063-8. All rights reserved.

Cd1−x Zn x Te films of various stoichiometries have been prepared by the two‐stage process. The technique involves sequentially depositing thin layers of Cd, Zn, and Te on a substrate and reacting these elemental layers to form the compound. Both electrodeposition and evaporation techniques have been used in this work to deposit the elemental films.Properties of the electroplated elemental films, as well as the structural, optical and electrical characteristics of the reacted compounds, have been studied. Transparent ZnTefilms of low resistivity have been obtained. Cd1−x Zn x Te/CdS solar cells using films processed by the two‐stage technique are demonstrated.

A two-stage process was used to prepare polycrystalline thin films of CuInSe2 for solar cell applications. The technique involves first depositing thin layers of copper and indium on a substrate and then selenizing this metallic stack to form CuInSe2. Both electron-beam evaporation and evaporation from resistively heated boats were used to deposit the copper and indium films. Selenization was carried out in an H2Se atmosphere at 400 °C. CuInSe2 films obtained from uniformly deposited metallic layers were found to be of chalcopyrite phase. Heterojunction solar cells with efficiencies close to 11% have been fabricated on these films.

A simple two-stage process is utilized to prepare ZnTe thin films. The technique involves electrodeposition of tellurium and zinc stacked layers out of aqueous electrolytes and reaction of them in an inert atmosphere. The resulting films will be used in cascade solar cell structures.

Electroplated CdS/p-Hg1−x Cdx Te (MCT) thin-film solar cells with (1 - x) are evaluated and compared with electroplated CdS/p-CdTe devices. It is shown that the series resistance limitations commonly observed in CdS/p-CdTe devices can be appreciably reduced if p-CdTe is replaced by p-MCT. This is due to the lower resistivities attainable in p-MCT thin films which in turn reduce both bulk and contact resistances. The possiblity of bandgap control in MCT makes it an important candidate material for the production of high-efficiency tandem cells.

The processing steps necessary for producing high efficiency electrodeposited CdTe and HgCdTe solar cells are described. The key step in obtaining solar cell grade p-type CdTe and HgCdTe is the “type conversion-junction formation” (TCJF) process. The TCJF process involves the heat treatment of the as-deposited n-type CdTe and HgCdTe layers at around 400 °C. This procedure converts these n-type films into high resistivity p type and forms a rectifying junction between them and the underlying n-type window layers. Possible effects of oxygen on the TCJF process are discussed. The results of studies made on the structural, electrical and optical properties of the electrodeposited CdS, CdTe and HgCdTe films are presented. The resistivity of the electrodeposited HgCdTe can be made lower than that of CdTe. Consequently, solar cells made using the HgCdTe films have, on the average, better fill factors than those made using the CdTe layers. HgCdTe is also attractive for tandem-cell applications because of its variable band gap which can be easily tuned to the desired value. CdS/CdTe and CdS/HgCdTe heterojunction solar cells with 10.3% and 10.6% efficiency have been demonstrated using electrodeposition techniques and the TCJF process.

Cd‐rich mercury cadmium telluride (MCT) is a promising material for thin‐film solar cell applications. In this letter we present data on the deposition of MCT films by a simple electroplating technique and report on the highest efficiency polycrystalline MCT thin‐film solar cell to date, which has an efficiency of 10.6% under AM1.5 illumination.

Over 9% efficiency is demonstrated in electroplated CdS/CdTe thin film solar cells. Processing of the devices is described. A brief heat treatment step first anneals out the deep lifetime killer centers in the material then converts the originally n‐type film into solar cell grade p‐CdTe.

The latest in a series of solar cells made using electrochemical deposition is the CdS/p-CdTe heterojunction described here. The two ultrathin polycrystalline active layers were electrodeposited to yield cells with an efficiency of 7% over 0.2 cm2 area. Best observed solar cell parameters were VOC = 0.79 V, JSC =18.8 mA/cm2 and F.F. =0.56 under illumination of 100 mW/cm2. An improved window material should increase the efficiency of this potentially lew-cost cell.

A technique is described to determine the optical absorption coefficients of semiconductor films. This technique uses the spectral response of solar cells formed on these films. Under certain conditions the photogenerated current in a back‐wall solar cell is a simple exponential function of the absorption coefficient and the thickness of the device. As a result the optical absorption coefficients can be obtained from the slopes of log (I) versus thickness curves at different wavelengths. The technique was applied to electrochemically deposited CdTe and gave results that are in agreement with other published work.