Dimitrios Hariskos - Academia.edu (original) (raw)
Papers by Dimitrios Hariskos
Journal of Applied Physics, 2015
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
Energy Procedia, 2011
Optoelectronic properties relevant for photovoltaics, such as band gap, spectral absorption, and ... more Optoelectronic properties relevant for photovoltaics, such as band gap, spectral absorption, and splitting of quasi-Fermi levels of chalcopyrites Cu(In,Ga)Se 2 have been analyzed by luminescence with lateral highly resolved methods, such as confocal photoluminescence (PL) ( 1 μm). In addition to the high lateral resolution we get access to depth profiles via different samples thicknesses provided by etching of standard samples. Amongst lateral fluctuations of band gap (up to few tens of meV), spectral absorption, and splitting of quasi-Fermi levels ( (E Fn -E Fp ) (20-30) meV) we identify the increase in band gap corresponding to the rise in Ga content towards the rear contact; we also see by luminescence a substantial lateral fluctuation of the band gap which is interpreted as an according large lateral fluctuation of the extension of the Ga depth profile towards the front side. This observation agrees well with lateral variations of (E Fn -E Fp ) that cannot be consistently interpreted without sufficient spatial resolution.
Conference Record of the Twenty Third IEEE Photovoltaic Specialists Conference - 1993 (Cat. No.93CH3283-9), 1993
This paper reports results from experiments concerning the growth of CuInSe2 films on different s... more This paper reports results from experiments concerning the growth of CuInSe2 films on different substrate materials, uncoated, and coated with molybdenum. Specifically the effect on the structure, i.e. preferred orientation, of the polycrystalline films is investigated. It is found that soda-lime float glass results in the most oriented films and also that the highest solar cell conversion efficiency is obtained
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
CuInSe2 (CIS) and related compounds have demonstrated their high potential for high efficiency th... more CuInSe2 (CIS) and related compounds have demonstrated their high potential for high efficiency thin film solar cells. A key issue for the development of modules is upscaling of the CIS absorber deposition. Different preparation methods have been applied. For transferring all process steps on large area with high throughput and process yield, the strategy is to optimize the methods available
Conference Record of the Twenty Third IEEE Photovoltaic Specialists Conference - 1993 (Cat. No.93CH3283-9), 1993
In this contribution the interest is centered on interaction phenomena that occur between the CuI... more In this contribution the interest is centered on interaction phenomena that occur between the CuInSe2, the chemical bath deposition (CBD) used to grow buffer layers and the RF sputtered ZnO windows. The potential output of a better understanding of these interfacial aspects is to permit high quality device synthesis, not only without the use of Cd, but without the need of interrupting the vacuum processing between the absorber and the window synthesis. Direct CuInSe 2/ZnO structures are optimized here to be 10.5% efficient, limited only by their low (less than 400 mV) open circuit voltages. Different methods were explored to try to overcome these limiting mechanisms and attempts were made using jV(T) analysis to identify them. The Voc can be improved by the use of (CBD) buffer layers, well known for CdS but also true for a list of other materials. The reasons for such results are possibly at the interfacial chemistry level
Thin Solid Films, 2011
Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu... more Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se2 (CIGS) module manufacturing. Although innovative concepts like rotatable magnetron sputtering from ceramic targets have been realised, costs are still high due to expensive ceramic targets. Significant cost reductions are expected by using reactive sputtering of metallic targets.Therefore, ZSW and industrial partners investigated the reactive sputtering of Al-doped zinc oxide (ZAO) as TCO on CIGS absorbers of high quality and industrial relevance. The reactive DC sputtering from rotatable magnetron targets is controlled in the transition mode by adjusting oxygen flow and discharge voltage. Optimisation leads to ZAO films with a TCO quality nearly comparable to standard films deposited by DC ceramic sputtering. Scanning electron microscopy, X-ray diffraction, and Hall analyses of the ZAO films are performed.Medium-size CIGS modules are coated with reactively sputtered ZAO, resulting in 12.8% module efficiency and surpassing the efficiency of the ceramic witness device. Cd-free buffered devices are also successfully coated with reactive TCO. Damp heat stability according to IEC61646 is met by all reactively sputtered devices.
Thin Solid Films, 2004
The development of Cd-free buffer layers by vacuum process for Cu (In, Ga) Se2 (CIGS) solar modul... more The development of Cd-free buffer layers by vacuum process for Cu (In, Ga) Se2 (CIGS) solar modules becomes even more interesting regarding environmental aspects and the implementation in industrial production. This work presents the latest results of CIGS ...
IEEE Journal of Photovoltaics, 2015
ABSTRACT New processing developments in the Cu(In,Ga)Se2 (CIGS)-based solar cell technology have ... more ABSTRACT New processing developments in the Cu(In,Ga)Se2 (CIGS)-based solar cell technology have enabled best cell efficiencies to exceed 21%. The key innovation involves the alkali post-deposition treatment (PDT) of the CIGS film. Furthermore, the range of optimal CIGS growth parameters and the minimal thickness of the CdS buffer layer is affected by the process modifications. In 2013, we reported a 20.8% record device with PDT. Later optimizations, e.g., in the composition profile and CdS buffer layer thickness as discussed in this study, enabled us to increase the photocurrent density with only a slight loss in open-circuit voltage and unchanged fill factor, resulting in the current world record of 21.7% efficiency. Furthermore, a record efficiency of 21.0% could be achieved with a Cd-free Zn(O,S) buffer layer. This contribution presents measurements, simulations, and a discussion of the photocurrent increase.
Computational Materials Science
The nucleation and growth of voids in a particle-reinforced metal matrix composite (MMC) material... more The nucleation and growth of voids in a particle-reinforced metal matrix composite (MMC) material have been modelled using internal state variable equations implemented in a unit-cell finite element model.
Vakuum in Forschung und Praxis, 2014
ABSTRACT This contribution provides an overview of current activities in the area of alternative ... more ABSTRACT This contribution provides an overview of current activities in the area of alternative buffer layers for Cu(In,Ga)(S,Se)2 (CIGS) thin-film solar cells. Good cell and module results were achieved by replacing the standard Cds buffer with Zn(O,S), In2S3, (Zn,Sn)Oy or (Zn,Mg)O grown by various methods like chemical bath deposition (CBD), thermal evaporation, sputtering, atomic layer deposition, and spray ion layer gas reaction. The “dry” deposition methods like sputtering and thermal evaporation could be favorable in an industrial environment on glass substrates or application in a roll-to-roll coater. Significant progress was made within the last two years for various Cd-free CIGS devices. We list current records for cells with alternative buffers, e. g. Zn(O,S)-buffered champion cells with efficiencies between 18—20 % and In2S3-buffered cells with 16—17 %. Both materials have the potential to substitute CdS with efficiencies approaching the 20 % mark already surpassed by CIGS cells with CBD CdS buffers. Substitution der CdS-Pufferschicht in CIGS-Dünnschichtsolarzellen Dieser Artikel gibt einen überblick über aktuelle Aktivitäten zu alternativen Pufferschichten für Cu(In,Ga)(S,Se)2 (CIGS-) Dünnschichtsolarzellen. Gute Zell- und Modulergebnisse wurden durch Ersetzen des standardmäßigen CdS mit Zn(O,S), In2S3, (Zn,Sn)Oy oder (Zn,Mg)O erzielt, die durch verschiedenste Verfahren wie Deposition aus dem chemischen Bad (CBD), thermisches Verdampfen, Sputtern, Atomlagenabscheidung und Sprüh-ILGAR abgeschieden wurden. „Trockene” Beschichtungsverfahren wie sputtern oder thermisches Verdampfen können in einer industriellen Umgebung mit Glassubstraten oder einer Rolle-zu-Rolle Beschichtung vorteilhaft sein. Enorme Fortschritte wurden innerhalb der letzten zwei Jahre für verschiedene Cd-freie CIGS-Bauteile erzielt. Aktuelle Rekordwirkungsgrade z. B. für Zn(O,S)-gepufferte Zellen liegen im Bereich 18—20 % sowie für In2S3 bei 16—17 %, also nahe an den Rekordwerten von über 20 % für CIGS-Zellen mit CBD CdS-Puffern und zeigen, dass beide Materialien das Potenzial besitzen CdS zu ersetzen.
Atomic layer deposited In2S3 has been already qualified as an alternative to the traditional CdS ... more Atomic layer deposited In2S3 has been already qualified as an alternative to the traditional CdS buffer layer used in CIGS solar cells. Magnetron sputtering is a well developed large area deposition method and can easily be implemented in a production line for CIGS modules. In this work we investigated the potential of magnetron sputtered In2S3 buffer for CIGS solar cells. Using two different sputtering systems, the In2S3 was deposited from a ceramic In2S3 target in Ar and from a metallic indium target in a H2S Ar gas mixture. Sputtering parameters such as plasma excitation rf dc, sputtering pressure, sputtering rate, power density, and deposition temperature were varied. The grown layers on glass or CIGS were characterized using SEM, transmission, XPS and SIMS. The best cell efficiencies of 12.2 were obtained with a sputtered In2S3 buffer from the ceramic target. 11.1 efficient cells were realized with the reactively sputtered In2S3 buffer from the metallic indium target
2012 IEEE 38th Photovoltaic Specialists Conference (PVSC) PART 2, 2012
ABSTRACT The long-term stability of solar cells is a crucial factor for the competitiveness of a ... more ABSTRACT The long-term stability of solar cells is a crucial factor for the competitiveness of a technology. In this study, the accelerated aging of CIGS solar cells was studied, and the influence of an applied bias during the endurance test on the open-circuit voltage Voc and fill factor (FF) was investigated. Time constants for parameter drifts of the open-circuit voltage and the associated activation energy were determined. The observed parameter drifts will be discussed, and a model will be proposed based on SCAPS simulations, explaining the observed behavior of the electrical characteristics of the solar cells. Therefore, cells were dark annealed under dry conditions at two different temperatures and different voltage biases were applied to the cells. Our study revealed that the application of a positive bias, which is similar to light soaking, first leads to an improvement and stabilization of the open-circuit voltage and FF followed by a slow decrease of these parameters. This long-term decrease can be explained in terms of a back barrier or phototransistor, as simulated with SCAPS. However, applying a positive bias enhances the long-term stability of these devices. The appearance of a back barrier is associated with a time constant exceeding 30 years. Therefore, this degradation mechanism is not critical.
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
In this work, the nucleation and growth of the CdS buffer layer (chemical bath deposition) on Cu(... more In this work, the nucleation and growth of the CdS buffer layer (chemical bath deposition) on Cu(In,Ga)Se2. (CIGS) thin films was observed using the surface-specific methods of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The AFM images show islands at short deposition times (<30 s) whereas XPS measurements do not register any sulfur on these surfaces. The authors postulate that Cd(OH)2 precipitates out of the basic deposition solution while rinsing it off the CIGS surface, thus creating the islands. All methods used here indicate the onset of bulk CdS growth after about 30 s deposition time. According to the AFM images, the entire CIGS surface seems to be covered within 1 min deposition. This is confirmed by SE, which shows bulk layer growth after 1 min; it increases at about 0.4 nm/s after the induction phase
physica status solidi (RRL) - Rapid Research Letters, 2015
ABSTRACT No abstract is available for this article.
physica status solidi (RRL) - Rapid Research Letters, 2014
ABSTRACT We report on a new thin-film Cu(In,Ga)Se2 (CIGS) solar cell record efficiency of 21.7%. ... more ABSTRACT We report on a new thin-film Cu(In,Ga)Se2 (CIGS) solar cell record efficiency of 21.7%. In order to better understand this newest development, we describe the specific solar cell data as obtained from I–V measurement and diode analysis, quantum efficiency and secondary neutral mass spectrometry measurements. We hope that such a description will help to exploit the potential of this promising thin-film solar technology even further. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
Surface and Interface Analysis, 2013
ABSTRACT Zn(O,S) is a promising candidate to replace the commonly used CdS buffer layer for Cu(In... more ABSTRACT Zn(O,S) is a promising candidate to replace the commonly used CdS buffer layer for Cu(In,Ga)Se2 (CIGS) thin-film solar cells due to its non-toxicity and its potential to enhance the conversion efficiency of the CIGS solar cell. The composition of chemical bath deposited (CBD) and sputtered Zn(O,S) layers with thicknesses well below 100 nm was determined by sputtered neutral and secondary ion mass spectrometry (SNMS and SIMS). Despite numerous mass interferences of double-charged atoms and dimers with single Zn, O and S isotopes, we developed an evaluation algorithm for quantification of SNMS depth profiles of Zn(O,S) layers. In particular, the superposition of double-charged S and Zn atoms with O and S isotopes is accounted for numerically in the quantification procedure. For sputtered Zn(O,S) layers, the S/(S + O) atomic ratio and the vertical composition profile can be controlled by the O2 content in the gas flow and the substrate temperature during sputtering whereas for CBD Zn(O,S) the S/(S +
Reliability of Photovoltaic Cells, Modules, Components, and Systems VI, 2013
ABSTRACT CIGS is the most promising technology for thin-film solar cells with record efficiencies... more ABSTRACT CIGS is the most promising technology for thin-film solar cells with record efficiencies of 20.4 % on laboratory scale and 17.8 % aperture area efficiency on a 900 cm² module. Another important factor besides the cell efficiency is the reliability and long term stability of the manufactured modules, which can be assessed by accelerated ageing. In this contribution the accelerated ageing of CIGS mini modules has been investigated. Therefore, modules were dark annealed under dry heat conditions at different temperatures. During the endurance test a positive or negative bias was applied to the cells. In regular intervals the IV- and CV-characteristics were measured at room temperature. After an overall stress time of 3500 h the IV-characteristics were determined under different illumination conditions (intensity, spectral illumination). Our previous publications suggest a barrier at the back contact to explain the observed parameter drifts. This contribution is focused on the influence of different bias conditions during the endurance test on the generation of a back diode and on the change of the acceptor concentration. These parameter drifts have an impact on the open circuit voltage, fill factor and on the appearance of a cross over between dark and illuminated IV-characteristics. The interpretation of the observed parameter drifts was supported by SCAPS simulations based on the above mentioned back barrier model. As an outcome of the simulations signatures for the existence of a back barrier diode were established. IVmeasurements, temperature dependent Voc measurements and SunsVoc measurements are helpful means to detect such back diodes.
Journal of Applied Physics, 2015
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
Energy Procedia, 2011
Optoelectronic properties relevant for photovoltaics, such as band gap, spectral absorption, and ... more Optoelectronic properties relevant for photovoltaics, such as band gap, spectral absorption, and splitting of quasi-Fermi levels of chalcopyrites Cu(In,Ga)Se 2 have been analyzed by luminescence with lateral highly resolved methods, such as confocal photoluminescence (PL) ( 1 μm). In addition to the high lateral resolution we get access to depth profiles via different samples thicknesses provided by etching of standard samples. Amongst lateral fluctuations of band gap (up to few tens of meV), spectral absorption, and splitting of quasi-Fermi levels ( (E Fn -E Fp ) (20-30) meV) we identify the increase in band gap corresponding to the rise in Ga content towards the rear contact; we also see by luminescence a substantial lateral fluctuation of the band gap which is interpreted as an according large lateral fluctuation of the extension of the Ga depth profile towards the front side. This observation agrees well with lateral variations of (E Fn -E Fp ) that cannot be consistently interpreted without sufficient spatial resolution.
Conference Record of the Twenty Third IEEE Photovoltaic Specialists Conference - 1993 (Cat. No.93CH3283-9), 1993
This paper reports results from experiments concerning the growth of CuInSe2 films on different s... more This paper reports results from experiments concerning the growth of CuInSe2 films on different substrate materials, uncoated, and coated with molybdenum. Specifically the effect on the structure, i.e. preferred orientation, of the polycrystalline films is investigated. It is found that soda-lime float glass results in the most oriented films and also that the highest solar cell conversion efficiency is obtained
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
CuInSe2 (CIS) and related compounds have demonstrated their high potential for high efficiency th... more CuInSe2 (CIS) and related compounds have demonstrated their high potential for high efficiency thin film solar cells. A key issue for the development of modules is upscaling of the CIS absorber deposition. Different preparation methods have been applied. For transferring all process steps on large area with high throughput and process yield, the strategy is to optimize the methods available
Conference Record of the Twenty Third IEEE Photovoltaic Specialists Conference - 1993 (Cat. No.93CH3283-9), 1993
In this contribution the interest is centered on interaction phenomena that occur between the CuI... more In this contribution the interest is centered on interaction phenomena that occur between the CuInSe2, the chemical bath deposition (CBD) used to grow buffer layers and the RF sputtered ZnO windows. The potential output of a better understanding of these interfacial aspects is to permit high quality device synthesis, not only without the use of Cd, but without the need of interrupting the vacuum processing between the absorber and the window synthesis. Direct CuInSe 2/ZnO structures are optimized here to be 10.5% efficient, limited only by their low (less than 400 mV) open circuit voltages. Different methods were explored to try to overcome these limiting mechanisms and attempts were made using jV(T) analysis to identify them. The Voc can be improved by the use of (CBD) buffer layers, well known for CdS but also true for a list of other materials. The reasons for such results are possibly at the interfacial chemistry level
Thin Solid Films, 2011
Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu... more Sputtering ZnO as transparent front contact (TCO) is standard in today's industrial scale Cu(In,Ga)Se2 (CIGS) module manufacturing. Although innovative concepts like rotatable magnetron sputtering from ceramic targets have been realised, costs are still high due to expensive ceramic targets. Significant cost reductions are expected by using reactive sputtering of metallic targets.Therefore, ZSW and industrial partners investigated the reactive sputtering of Al-doped zinc oxide (ZAO) as TCO on CIGS absorbers of high quality and industrial relevance. The reactive DC sputtering from rotatable magnetron targets is controlled in the transition mode by adjusting oxygen flow and discharge voltage. Optimisation leads to ZAO films with a TCO quality nearly comparable to standard films deposited by DC ceramic sputtering. Scanning electron microscopy, X-ray diffraction, and Hall analyses of the ZAO films are performed.Medium-size CIGS modules are coated with reactively sputtered ZAO, resulting in 12.8% module efficiency and surpassing the efficiency of the ceramic witness device. Cd-free buffered devices are also successfully coated with reactive TCO. Damp heat stability according to IEC61646 is met by all reactively sputtered devices.
Thin Solid Films, 2004
The development of Cd-free buffer layers by vacuum process for Cu (In, Ga) Se2 (CIGS) solar modul... more The development of Cd-free buffer layers by vacuum process for Cu (In, Ga) Se2 (CIGS) solar modules becomes even more interesting regarding environmental aspects and the implementation in industrial production. This work presents the latest results of CIGS ...
IEEE Journal of Photovoltaics, 2015
ABSTRACT New processing developments in the Cu(In,Ga)Se2 (CIGS)-based solar cell technology have ... more ABSTRACT New processing developments in the Cu(In,Ga)Se2 (CIGS)-based solar cell technology have enabled best cell efficiencies to exceed 21%. The key innovation involves the alkali post-deposition treatment (PDT) of the CIGS film. Furthermore, the range of optimal CIGS growth parameters and the minimal thickness of the CdS buffer layer is affected by the process modifications. In 2013, we reported a 20.8% record device with PDT. Later optimizations, e.g., in the composition profile and CdS buffer layer thickness as discussed in this study, enabled us to increase the photocurrent density with only a slight loss in open-circuit voltage and unchanged fill factor, resulting in the current world record of 21.7% efficiency. Furthermore, a record efficiency of 21.0% could be achieved with a Cd-free Zn(O,S) buffer layer. This contribution presents measurements, simulations, and a discussion of the photocurrent increase.
Computational Materials Science
The nucleation and growth of voids in a particle-reinforced metal matrix composite (MMC) material... more The nucleation and growth of voids in a particle-reinforced metal matrix composite (MMC) material have been modelled using internal state variable equations implemented in a unit-cell finite element model.
Vakuum in Forschung und Praxis, 2014
ABSTRACT This contribution provides an overview of current activities in the area of alternative ... more ABSTRACT This contribution provides an overview of current activities in the area of alternative buffer layers for Cu(In,Ga)(S,Se)2 (CIGS) thin-film solar cells. Good cell and module results were achieved by replacing the standard Cds buffer with Zn(O,S), In2S3, (Zn,Sn)Oy or (Zn,Mg)O grown by various methods like chemical bath deposition (CBD), thermal evaporation, sputtering, atomic layer deposition, and spray ion layer gas reaction. The “dry” deposition methods like sputtering and thermal evaporation could be favorable in an industrial environment on glass substrates or application in a roll-to-roll coater. Significant progress was made within the last two years for various Cd-free CIGS devices. We list current records for cells with alternative buffers, e. g. Zn(O,S)-buffered champion cells with efficiencies between 18—20 % and In2S3-buffered cells with 16—17 %. Both materials have the potential to substitute CdS with efficiencies approaching the 20 % mark already surpassed by CIGS cells with CBD CdS buffers. Substitution der CdS-Pufferschicht in CIGS-Dünnschichtsolarzellen Dieser Artikel gibt einen überblick über aktuelle Aktivitäten zu alternativen Pufferschichten für Cu(In,Ga)(S,Se)2 (CIGS-) Dünnschichtsolarzellen. Gute Zell- und Modulergebnisse wurden durch Ersetzen des standardmäßigen CdS mit Zn(O,S), In2S3, (Zn,Sn)Oy oder (Zn,Mg)O erzielt, die durch verschiedenste Verfahren wie Deposition aus dem chemischen Bad (CBD), thermisches Verdampfen, Sputtern, Atomlagenabscheidung und Sprüh-ILGAR abgeschieden wurden. „Trockene” Beschichtungsverfahren wie sputtern oder thermisches Verdampfen können in einer industriellen Umgebung mit Glassubstraten oder einer Rolle-zu-Rolle Beschichtung vorteilhaft sein. Enorme Fortschritte wurden innerhalb der letzten zwei Jahre für verschiedene Cd-freie CIGS-Bauteile erzielt. Aktuelle Rekordwirkungsgrade z. B. für Zn(O,S)-gepufferte Zellen liegen im Bereich 18—20 % sowie für In2S3 bei 16—17 %, also nahe an den Rekordwerten von über 20 % für CIGS-Zellen mit CBD CdS-Puffern und zeigen, dass beide Materialien das Potenzial besitzen CdS zu ersetzen.
Atomic layer deposited In2S3 has been already qualified as an alternative to the traditional CdS ... more Atomic layer deposited In2S3 has been already qualified as an alternative to the traditional CdS buffer layer used in CIGS solar cells. Magnetron sputtering is a well developed large area deposition method and can easily be implemented in a production line for CIGS modules. In this work we investigated the potential of magnetron sputtered In2S3 buffer for CIGS solar cells. Using two different sputtering systems, the In2S3 was deposited from a ceramic In2S3 target in Ar and from a metallic indium target in a H2S Ar gas mixture. Sputtering parameters such as plasma excitation rf dc, sputtering pressure, sputtering rate, power density, and deposition temperature were varied. The grown layers on glass or CIGS were characterized using SEM, transmission, XPS and SIMS. The best cell efficiencies of 12.2 were obtained with a sputtered In2S3 buffer from the ceramic target. 11.1 efficient cells were realized with the reactively sputtered In2S3 buffer from the metallic indium target
2012 IEEE 38th Photovoltaic Specialists Conference (PVSC) PART 2, 2012
ABSTRACT The long-term stability of solar cells is a crucial factor for the competitiveness of a ... more ABSTRACT The long-term stability of solar cells is a crucial factor for the competitiveness of a technology. In this study, the accelerated aging of CIGS solar cells was studied, and the influence of an applied bias during the endurance test on the open-circuit voltage Voc and fill factor (FF) was investigated. Time constants for parameter drifts of the open-circuit voltage and the associated activation energy were determined. The observed parameter drifts will be discussed, and a model will be proposed based on SCAPS simulations, explaining the observed behavior of the electrical characteristics of the solar cells. Therefore, cells were dark annealed under dry conditions at two different temperatures and different voltage biases were applied to the cells. Our study revealed that the application of a positive bias, which is similar to light soaking, first leads to an improvement and stabilization of the open-circuit voltage and FF followed by a slow decrease of these parameters. This long-term decrease can be explained in terms of a back barrier or phototransistor, as simulated with SCAPS. However, applying a positive bias enhances the long-term stability of these devices. The appearance of a back barrier is associated with a time constant exceeding 30 years. Therefore, this degradation mechanism is not critical.
Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996, 1996
In this work, the nucleation and growth of the CdS buffer layer (chemical bath deposition) on Cu(... more In this work, the nucleation and growth of the CdS buffer layer (chemical bath deposition) on Cu(In,Ga)Se2. (CIGS) thin films was observed using the surface-specific methods of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). The AFM images show islands at short deposition times (<30 s) whereas XPS measurements do not register any sulfur on these surfaces. The authors postulate that Cd(OH)2 precipitates out of the basic deposition solution while rinsing it off the CIGS surface, thus creating the islands. All methods used here indicate the onset of bulk CdS growth after about 30 s deposition time. According to the AFM images, the entire CIGS surface seems to be covered within 1 min deposition. This is confirmed by SE, which shows bulk layer growth after 1 min; it increases at about 0.4 nm/s after the induction phase
physica status solidi (RRL) - Rapid Research Letters, 2015
ABSTRACT No abstract is available for this article.
physica status solidi (RRL) - Rapid Research Letters, 2014
ABSTRACT We report on a new thin-film Cu(In,Ga)Se2 (CIGS) solar cell record efficiency of 21.7%. ... more ABSTRACT We report on a new thin-film Cu(In,Ga)Se2 (CIGS) solar cell record efficiency of 21.7%. In order to better understand this newest development, we describe the specific solar cell data as obtained from I–V measurement and diode analysis, quantum efficiency and secondary neutral mass spectrometry measurements. We hope that such a description will help to exploit the potential of this promising thin-film solar technology even further. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)
Surface and Interface Analysis, 2013
ABSTRACT Zn(O,S) is a promising candidate to replace the commonly used CdS buffer layer for Cu(In... more ABSTRACT Zn(O,S) is a promising candidate to replace the commonly used CdS buffer layer for Cu(In,Ga)Se2 (CIGS) thin-film solar cells due to its non-toxicity and its potential to enhance the conversion efficiency of the CIGS solar cell. The composition of chemical bath deposited (CBD) and sputtered Zn(O,S) layers with thicknesses well below 100 nm was determined by sputtered neutral and secondary ion mass spectrometry (SNMS and SIMS). Despite numerous mass interferences of double-charged atoms and dimers with single Zn, O and S isotopes, we developed an evaluation algorithm for quantification of SNMS depth profiles of Zn(O,S) layers. In particular, the superposition of double-charged S and Zn atoms with O and S isotopes is accounted for numerically in the quantification procedure. For sputtered Zn(O,S) layers, the S/(S + O) atomic ratio and the vertical composition profile can be controlled by the O2 content in the gas flow and the substrate temperature during sputtering whereas for CBD Zn(O,S) the S/(S +
Reliability of Photovoltaic Cells, Modules, Components, and Systems VI, 2013
ABSTRACT CIGS is the most promising technology for thin-film solar cells with record efficiencies... more ABSTRACT CIGS is the most promising technology for thin-film solar cells with record efficiencies of 20.4 % on laboratory scale and 17.8 % aperture area efficiency on a 900 cm² module. Another important factor besides the cell efficiency is the reliability and long term stability of the manufactured modules, which can be assessed by accelerated ageing. In this contribution the accelerated ageing of CIGS mini modules has been investigated. Therefore, modules were dark annealed under dry heat conditions at different temperatures. During the endurance test a positive or negative bias was applied to the cells. In regular intervals the IV- and CV-characteristics were measured at room temperature. After an overall stress time of 3500 h the IV-characteristics were determined under different illumination conditions (intensity, spectral illumination). Our previous publications suggest a barrier at the back contact to explain the observed parameter drifts. This contribution is focused on the influence of different bias conditions during the endurance test on the generation of a back diode and on the change of the acceptor concentration. These parameter drifts have an impact on the open circuit voltage, fill factor and on the appearance of a cross over between dark and illuminated IV-characteristics. The interpretation of the observed parameter drifts was supported by SCAPS simulations based on the above mentioned back barrier model. As an outcome of the simulations signatures for the existence of a back barrier diode were established. IVmeasurements, temperature dependent Voc measurements and SunsVoc measurements are helpful means to detect such back diodes.