Direct deposition of 10–15-μm-thick silicon layers onto foreign substrates yields a polycrystalli... more Direct deposition of 10–15-μm-thick silicon layers onto foreign substrates yields a polycrystalline Si material with an average grain size in the range 1–5 μm. The strong electrical activation of such large density and small grains is detrimental to solar cell performances. Here we investigate the passivation of such defects by ECR plasma hydrogenation. The electron beam induced current (EBIC) technique
A two-dimensional device modeling for polycrystalline silicon thin-film solar cells was performed... more A two-dimensional device modeling for polycrystalline silicon thin-film solar cells was performed. A ThRee-dimensional Emitter Based on Locally Enhanced diffusion (TREBLE) concept was applied to evaluate the degree of leveling of the device efficiency. The model ...
A novel chemical close-spaced vapor transport (CCSVT) technique has been developed for the growth... more A novel chemical close-spaced vapor transport (CCSVT) technique has been developed for the growth of the CuGaSe2 (CGSe) thin films on areas as large as 10×10 cm2. Cu precursors deposited on clean and Mo-coated soda lime glass substrates are thermally and chemically treated under gaseous GaClx/H2Se atmosphere in the CCSVT cell. The Ga2Se3 employed as source material is stoichiometrically volatilised
The microstructure of the CuGaSe2 (CGSe) thin films deposited by a novel chemical close-spaced va... more The microstructure of the CuGaSe2 (CGSe) thin films deposited by a novel chemical close-spaced vapour transport (CCSVT) technique on clean and Mo-coated soda lime glass (SLG) substrates has been investigated by transmission electron microscopy (TEM). The CGSe bulk and the interface between the CGSe and Mo films have been investigated. The as-grown CGSe films possess high bulk crystalline quality. At the CGSe/Mo interface, a MoSe2 interfacial layer (∼20–40 nm) has been observed and also an excess of Ga. Additionally, composition measurements and depth profiling of the elements were performed by elastic recoil detection analysis (ERDA). It has been found that the CGSe constituent elements are homogeneously distributed in the bulk, whereas the surface composition is influenced by the [Ga]/[Cu] ratio in the film. With the [Ga]/[Cu] ratio increase, the CGSe surface composition changes from Ga- and Cu-poor, and Se-rich to Cu-poor, and Ga-and Se-rich. Photoluminescence (PL) spectroscopy has been used as a complementary technique to study the defect profiles at the CGSe front and rear sides as a function of the [Ga]/[Cu] ratio. The PL data support the results of structural investigations, pointing out higher Ga concentration at the films rear side.
Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum s... more Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1.88(6) eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1.82(3) eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe(2), showing evidence for the existence of very shallow acceptor levels of 5(1) and 10(1) meV, and thus suggesting the AgGaSe(2) phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag(2)Se and Ga(2)O(3) nanometer-scaled surface layers, as well as by Ag(2)Se inclusions in the bulk and Ag clusters at the layers' rear side.
CuGaSe2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential leve... more CuGaSe2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential level of electrical performance. In order to elucidate possible shortcomings of the electronic interface structure, we have studied the initial stage of the CdS/CGSe interface formation by use of a simple Cd2+/NH3 treatment. As in the case of low-gap chalcopyrites, we find a Cd-containing surface layer, in
The chemical and electronic surface and interface structure of CuGaSe2 thin films was investigate... more The chemical and electronic surface and interface structure of CuGaSe2 thin films was investigated by photoelectron spectroscopy. With bulk [Ga]/[Cu] ratios increasing from 0.94 to 1.39 a transition of the Cu:Ga:Se surface composition from 1:1:2 to 1:3:5 and a downward shift of the valence band maximum with respect to the Fermi energy were observed. The comparison with the conduction band minimum (CBM) of CdS reveals that at the CdS/CuGaSe2 interface the recombination barrier height simultaneously increases and a ``clifflike'' offset is formed to the CBM of CuGaSe2.
The authors report factors that limit the photovoltaic parameters of organic solar cells based on... more The authors report factors that limit the photovoltaic parameters of organic solar cells based on phtalocyanine:fullerene bulk heterojunction. They show that the device photovoltaic properties and their stability are strongly influenced by O2 impurities. Oxygen affects mostly the photoelectrical properties of the fullerene and the state of the interface between phtalocyanine and fullerene domains. The illumination of the devices, especially
Direct deposition of 10–15-μm-thick silicon layers onto foreign substrates yields a polycrystalli... more Direct deposition of 10–15-μm-thick silicon layers onto foreign substrates yields a polycrystalline Si material with an average grain size in the range 1–5 μm. The strong electrical activation of such large density and small grains is detrimental to solar cell performances. Here we investigate the passivation of such defects by ECR plasma hydrogenation. The electron beam induced current (EBIC) technique
A two-dimensional device modeling for polycrystalline silicon thin-film solar cells was performed... more A two-dimensional device modeling for polycrystalline silicon thin-film solar cells was performed. A ThRee-dimensional Emitter Based on Locally Enhanced diffusion (TREBLE) concept was applied to evaluate the degree of leveling of the device efficiency. The model ...
A novel chemical close-spaced vapor transport (CCSVT) technique has been developed for the growth... more A novel chemical close-spaced vapor transport (CCSVT) technique has been developed for the growth of the CuGaSe2 (CGSe) thin films on areas as large as 10×10 cm2. Cu precursors deposited on clean and Mo-coated soda lime glass substrates are thermally and chemically treated under gaseous GaClx/H2Se atmosphere in the CCSVT cell. The Ga2Se3 employed as source material is stoichiometrically volatilised
The microstructure of the CuGaSe2 (CGSe) thin films deposited by a novel chemical close-spaced va... more The microstructure of the CuGaSe2 (CGSe) thin films deposited by a novel chemical close-spaced vapour transport (CCSVT) technique on clean and Mo-coated soda lime glass (SLG) substrates has been investigated by transmission electron microscopy (TEM). The CGSe bulk and the interface between the CGSe and Mo films have been investigated. The as-grown CGSe films possess high bulk crystalline quality. At the CGSe/Mo interface, a MoSe2 interfacial layer (∼20–40 nm) has been observed and also an excess of Ga. Additionally, composition measurements and depth profiling of the elements were performed by elastic recoil detection analysis (ERDA). It has been found that the CGSe constituent elements are homogeneously distributed in the bulk, whereas the surface composition is influenced by the [Ga]/[Cu] ratio in the film. With the [Ga]/[Cu] ratio increase, the CGSe surface composition changes from Ga- and Cu-poor, and Se-rich to Cu-poor, and Ga-and Se-rich. Photoluminescence (PL) spectroscopy has been used as a complementary technique to study the defect profiles at the CGSe front and rear sides as a function of the [Ga]/[Cu] ratio. The PL data support the results of structural investigations, pointing out higher Ga concentration at the films rear side.
Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum s... more Thin films of chalcopyrite AgGaSe(2) have been successfully grown on glass and glass/molybdenum substrates using the technique of chemical close-spaced vapor transport. The high crystallinity of the samples is confirmed by grazing-incidence x-ray diffraction, scanning and transmission electron microscopy, and optical transmission/reflection spectroscopy. Here, two of the three expected direct optical bandgaps are found at 1.77(2) and 1.88(6) eV at 300 K. The lowest bandgap energy at 4 K is estimated to be 1.82(3) eV. Photoluminescence spectroscopy has further revealed the nature of the point defects within the AgGaSe(2), showing evidence for the existence of very shallow acceptor levels of 5(1) and 10(1) meV, and thus suggesting the AgGaSe(2) phase itself to exhibit a p-type conductivity. At the same time, electrical characterization by Hall, Seebeck and four-point-probe measurements indicate properties of a compensated semiconductor. The electrical properties of the investigated thin films are mainly influenced by the presence of Ag(2)Se and Ga(2)O(3) nanometer-scaled surface layers, as well as by Ag(2)Se inclusions in the bulk and Ag clusters at the layers' rear side.
CuGaSe2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential leve... more CuGaSe2 (CGSe)-based high-gap thin-film solar cells have to date not reached their potential level of electrical performance. In order to elucidate possible shortcomings of the electronic interface structure, we have studied the initial stage of the CdS/CGSe interface formation by use of a simple Cd2+/NH3 treatment. As in the case of low-gap chalcopyrites, we find a Cd-containing surface layer, in
The chemical and electronic surface and interface structure of CuGaSe2 thin films was investigate... more The chemical and electronic surface and interface structure of CuGaSe2 thin films was investigated by photoelectron spectroscopy. With bulk [Ga]/[Cu] ratios increasing from 0.94 to 1.39 a transition of the Cu:Ga:Se surface composition from 1:1:2 to 1:3:5 and a downward shift of the valence band maximum with respect to the Fermi energy were observed. The comparison with the conduction band minimum (CBM) of CdS reveals that at the CdS/CuGaSe2 interface the recombination barrier height simultaneously increases and a ``clifflike'' offset is formed to the CBM of CuGaSe2.
The authors report factors that limit the photovoltaic parameters of organic solar cells based on... more The authors report factors that limit the photovoltaic parameters of organic solar cells based on phtalocyanine:fullerene bulk heterojunction. They show that the device photovoltaic properties and their stability are strongly influenced by O2 impurities. Oxygen affects mostly the photoelectrical properties of the fullerene and the state of the interface between phtalocyanine and fullerene domains. The illumination of the devices, especially
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