| 1. |
- Adeleye, Damilola, et al.
(författare)
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Mitigation of Phase Separation in High Ga Cu(In,Ga)S2 Absorbers to Achieve ∼ 1 Volt 15.6% Power Conversion Efficiency
- 2023
-
Ingår i: 2023 IEEE 50th Photovoltaic Specialists Conference (PVSC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665460590 - 9781665460606
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Konferensbidrag (refereegranskat)abstract
- The use of Cu(In,Ga)S2 as a top cell in tandem solar cell, despite having suitable properties for such an application, is hampered by a high open-circuit voltage (VOC) deficit. The deficit arises from a poor optoelectronic quality of the absorbers - engendered by phase separation - and the inadequate translation of the optoelectronic quality of the absorber into device VOC. In this work, we report the role of first stage substrate temperature in the mitigation of phase separation and optimized Cu-excess during growth in Cu(In,Ga)S2, which leads to reduced VOC deficit, resulting in a device with 15.6 % PCE with a VOC of ∼ 981 mV when completed with atomic layer deposited (Zn,Sn)O and Al:ZnMgO transparent conductive oxide.
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| 2. |
- Ahvenniemi, Esko, et al.
(författare)
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Recommended reading list of early publications on atomic layer deposition-Outcome of the "Virtual Project on the History of ALD"
- 2017
-
Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 35:1
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Forskningsöversikt (refereegranskat)abstract
- Atomic layer deposition (ALD), a gas-phase thin film deposition technique based on repeated, self-terminating gas-solid reactions, has become the method of choice in semiconductor manufacturing and many other technological areas for depositing thin conformal inorganic material layers for various applications. ALD has been discovered and developed independently, at least twice, under different names: atomic layer epitaxy (ALE) and molecular layering. ALE, dating back to 1974 in Finland, has been commonly known as the origin of ALD, while work done since the 1960s in the Soviet Union under the name "molecular layering" (and sometimes other names) has remained much less known. The virtual project on the history of ALD (VPHA) is a volunteer-based effort with open participation, set up to make the early days of ALD more transparent. In VPHA, started in July 2013, the target is to list, read and comment on all early ALD academic and patent literature up to 1986. VPHA has resulted in two essays and several presentations at international conferences. This paper, based on a poster presentation at the 16th International Conference on Atomic Layer Deposition in Dublin, Ireland, 2016, presents a recommended reading list of early ALD publications, created collectively by the VPHA participants through voting. The list contains 22 publications from Finland, Japan, Soviet Union, United Kingdom, and United States. Up to now, a balanced overview regarding the early history of ALD has been missing; the current list is an attempt to remedy this deficiency.
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| 3. |
- Akbari-Saatlu, Mehdi, et al.
(författare)
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Nanometer-Thick ZnO/SnO2Heterostructures Grown on Alumina for H2S Sensing
- 2022
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:5, s. 6954-6963
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Tidskriftsartikel (refereegranskat)abstract
- Designing heterostructure materials at the nanoscale is a well-known method to enhance gas sensing performance. In this study, a mixed solution of zinc chloride and tin (II) chloride dihydrate, dissolved in ethanol solvent, was used as the initial precursor for depositing the sensing layer on alumina substrates using the ultrasonic spray pyrolysis (USP) method. Several ZnO/SnO2 heterostructures were grown by applying different ratios in the initial precursors. These heterostructures were used as active materials for the sensing of H2S gas molecules. The results revealed that an increase in the zinc chloride in the USP precursor alters the H2S sensitivity of the sensor. The optimal working temperature was found to be 450 °C. The sensor, containing 5:1 (ZnCl2: SnCl2·2H2O) ratio in the USP precursor, demonstrates a higher response than the pure SnO2 (∼95 times) sample and other heterostructures. Later, the selectivity of the ZnO/SnO2 heterostructures toward 5 ppm NO2, 200 ppm methanol, and 100 ppm of CH4, acetone, and ethanol was also examined. The gas sensing mechanism of the ZnO/SnO2 was analyzed and the remarkably enhanced gas-sensing performance was mainly attributed to the heterostructure formation between ZnO and SnO2. The synthesized materials were also analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, and X-ray photoelectron spectra to investigate the material distribution, grain size, and material quality of ZnO/SnO2 heterostructures.
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| 4. |
- Alberto, H. V., et al.
(författare)
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Slow-muon study of quaternary solar-cell materials : Single layers and p-n junctions
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:2
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Tidskriftsartikel (refereegranskat)abstract
- Thin films and p-n junctions for solar cells based on the absorber materials Cu(In, Ga) Se-2 and Cu2ZnSnS4 were investigated as a function of depth using implanted low energy muons. The most significant result is a clear decrease of the formation probability of the Mu(+) state at the heterojunction interface as well as at the surface of the Cu(In, Ga)Se-2 film. This reduction is attributed to a reduced bonding reaction of the muon in the absorber defect layer at its surface. In addition, the activation energies for the conversion from a muon in an atomiclike configuration to a anion-bound position are determined from temperature-dependence measurements. It is concluded that the muon probe provides a measurement of the effective surface defect layer width, both at the heterojunctions and at the films. The CIGS surface defect layer is crucial for solar-cell electrical performance and additional information can be used for further optimizations of the surface.
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| 5. |
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| 6. |
- Bilousov, Oleksandr V., et al.
(författare)
-
ALD of phase controlled tin monosulfide thin films
- 2017
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Konferensbidrag (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising semiconductor material for low-cost conversion of solar energy, playing the role of absorber layer in photovoltaic devices. SnS is, due to its high optical damping, also an excellent semiconductor candidate for the realization of ultrathin (nanoscale thickness) plasmonic solar cells [1].Here, we present an important step to further control and understand SnS film properties produced using low temperature ALD with Sn(acac)2 and H2S as precursors. We show that the SnS film properties vary over a rather wide range depending on substrate temperature and reaction conditions, and that this is connected to the growth of cubic (π-SnS) and orthorhombic SnS phases. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry [2].1. C. Hägglund, G. Zeltzer, R. Ruiz, A. Wangperawong, K. E. Roelofs, S. F. Bent, ACS Photonics 3 (3) (2016) 456–463.2. O. V. Bilousov, Y. Ren, T. Törndahl, O. Donzel-Gargand , T. Ericson, C. Platzer-Björkman, M. Edoff, and C. Hägglund, ACS Chemistry of Materials 29 (7) (2017) 2969–2978.
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| 7. |
- Bilousov, Oleksandr V., et al.
(författare)
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Atomic Layer Deposition of Cubic and Orthorhombic Phase Tin Monosulfide
- 2017
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 29:7, s. 2969-2978
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Tidskriftsartikel (refereegranskat)abstract
- Tin monosulfide (SnS) is a promising light-absorbing material with weak environmental constraints for application in thin film solar cells. In this paper, we present low-temperature atomic layer deposition (ALD) of high-purity SnS of both cubic and orthorhombic phases. Using tin(II) 2,4-pentanedionate [Sn(acac)(2)] and hydrogen sulfide (H2S) as precursors, controlled growth of the two polymorphs is achieved. Quartz crystal microbalance measurements are used to establish saturated conditions and show that the SnS ALD is self-limiting over temperatures from at least 80 to 160 degrees C. In this temperature window, a stable mass gain of 19 ng cm(-2) cycle(-1) is observed. The SnS thin film crystal structure and morphology undergo significant changes depending on the conditions. High-resolution transmission electron microscopy and X-ray diffraction demonstrate that fully saturated growth requires a large H2S dose and results in the cubic phase. Smaller H2S doses and higher temperatures favor the orthorhombic phase. The optical properties of the two polymorphs differ significantly, as demonstrated by spectroscopic ellipsometry. The orthorhombic phase displays a wide (0.3-0.4 eV) Urbach tail in the near-infrared region, ascribed to its nanoscale structural disorder and/or to sulfur vacancy-induced gap states. In contrast, the cubic phase is smooth and void-free and shows a well-defined, direct forbidden-type bandgap of 1.64 eV.
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| 8. |
- Choolakkal, Arun Haridas, 1992-
(författare)
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Conformal chemical vapor deposition of boron carbide thin films
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The sustainability goals of the modern world and the fascinating properties of sub-micron scale materials promote development of materials in thin film form. Thin films are materials that have thicknesses ranging from sub-nanometer to several micrometers, synthesized by various deposition techniques. They are used for diverse applications, such as light emitting diodes, solar cells, semiconductor chips, etc. The primary objective of this research project is to develop a chemical vapor deposition (CVD) process for conformal boron carbide thin films. Since boron carbide is a promising neutron converter material for solid-state neutron detectors, the process was validated by depositing on prototype detector chips. In this study, triethylboron (TEB) was used as single source CVD precursor to deposit boron carbide thin films. The initial experiments focused on low reaction rate deposition by depositing in a kinetically limited regime. The films deposited at ≤450 °C in 8:1 aspect ratio micro-trench structures were highly conformal and show a stoichiometry of about B5.2C. We attribute this observed conformality to the slow reaction kinetics of the TEB at the low deposition temperature enabling the diffusive transport of the precursor molecule down the trench. The depositions carried out on the prototype detector-chips show promising results. We expand our studies to investigate a new strategy with the prospect of improving the step coverage at higher temperatures for better film properties. We hypothesize that adding a suitable heavier molecule, diffusion additive, with an appropriate partial pressure can enhance the step coverage by pushing the lighter precursor molecule via competitive co-diffusion. It was tested by adding Xe gas to the boron carbide CVD from TEB. The result shows that with this diffusion additive the step coverage was improved from 0.71 to 0.97. From our experimental results, we suggest a competitive diffusion model that can be adapted to other CVD processes to enhance the film step coverage. The CVD process is further validated by depositing onto carbon nanotube membranes. The initial results show that the process was able to afford evenly deposition around the individual nanotubes in the carbon nanotube membrane. Raman spectroscopy measurements show a similar D-band to G-band intensity ratio before and after the deposition indicating that no defects were induced in the nanotubes.
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| 9. |
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| 10. |
- Donzel-Gargand, Olivier, et al.
(författare)
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Cu-depleted patches induced by presence of K during growth of CIGS absorbers
- 2017
-
Konferensbidrag (refereegranskat)abstract
- The conversion efficiency of the CIGS thin film solar cells has rapidly increased since introduction of the heavier alkali-doping (K, Rb, Cs). While the exclusive introduction of Na in the CIGS films has led to efficiencies up to 20,4% 1, the latest K, Rb or Cs post deposition treatments (PDT) have increased the efficiency to 22,6% 2. The exact role of this heavy-alkali PDT is still under discussion but three explanations have been discussed in the literature. First, that the heavy alkali PDT facilitates CdCu substitution, that results in an enhanced absorber type inversion, moving the p-n junction further into the CIGS bulk 3. Second, that the main effect from heavy alkali PDT is due to the formation of a K-In-Se2 layer, that passivates defects at the CIGS surface, reducing interface recombination 4. And third, that the heavy alkali PDT induces a Cu depletion at the surface of the CIGS which, by increasing the local Fermi level, increases the band bending; thus creating a higher potential barrier for holes to recombine 5.
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| 11. |
- Donzel-Gargand, Olivier, et al.
(författare)
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Deep surface Cu depletion induced by K in high-efficiency Cu(In,Ga)Se2 solar cell absorbers
- 2018
-
Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:9, s. 730-739
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we used K‐rich glass substrates to provide potassium during the coevaporation of Cu(In,Ga)Se2 (CIGS) absorber layers. Subsequently, we applied a postdeposition treatment (PDT) using KF or RbF to some of the grown absorbers. It was found that the presence of K during the growth of the CIGS layer led to cell effi- ciencies beyond 17%, and the addition of a PDT pushed it beyond 18%. The major finding of this work is the observation of discontinuous 100‐ to 200‐nm‐deep Cu‐ depleted patches in the vicinity of the CdS buffer layer, correlated with the presence of K during the growth of the absorber layer. The PDT had no influence on the forma- tion of these patches. A second finding concerns the composition of the Cu‐depleted areas, where an anticorrelation between Cu and both In and K was measured using scanning transmission electron microscopy. Furthermore, a steeper Ga/(In+Ga) ratio gradient was measured for the absorbers grown with the presence of K, suggesting that K hinders the group III element interdiffusion. Finally, no Cd in‐diffusion to the CIGS layer could be detected. This indicates that if CdCu substitution occurs, either their concentration is below our instrumental detection limit or its presence is contained within the first 6 nm from the CdS/CIGS interface.
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| 12. |
- Donzel-Gargand, Olivier, et al.
(författare)
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Secondary phase formation and surface modification from a high dose KF-post deposition treatment of (Ag,Cu)(In,Ga)Se-2 solar cell absorbers
- 2019
-
Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 27:3, s. 220-228
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we assessed the potential of KF-post deposition treatment (PDT) performed on a silver-alloyed Cu (In,Ga)Se-2 (ACIGS) solar absorber. ACIGS absorbers with Ag/Ag + Cu ratio (Ag/I) close to 20% were co-evaporated on a Mo-coated glass substrate and exposed to in-situ KF-PDT of various intensities. The current-voltage characteristics indicated that an optimized PDT can be beneficial, increasing in our study the median V-oc and efficiency values by +48 mV and + 0.9%(abs) (from 728 mV and 16.1% efficiency measured for the sample without PDT), respectively. However, an increased KF-flux during PDT resulted in a net deterioration of the performance leading to median V-oc and efficiency values as low as 503 mV and 4.7%. The chemical composition analysis showed that while the reference absorber without any post deposition treatment (PDT) was homogeneous, the KF-PDT induced a clear change within the first 10 nm from the surface. Here, the surface layer composition was richer in K and In with an increased Ag/I ratio, and its thickness seemed to follow the KF exposure intensity. Additionally, high-dose KF-PDT resulted in substantial formation of secondary phases for the ACIGS. The secondary phase precipitates were also richer in Ag, K, and In, and electron and X-ray diffraction data match with the monoclinic C 1 2/c 1 space group adopted by the Ag-alloyed KInSe2 phase. It could not be concluded whether the performance loss for the solar cell devices originated from the thicker surface layer or the presence of secondary phases, or both for the high-dose KF-PDT sample.
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| 13. |
- Donzel-Gargand, Olivier, et al.
(författare)
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Surface Modification And Secondary Phase Formation From a High Dose KF-Post Deposition Treatment of (Ag,Cu)(In,Ga)Se2 Solar Cell Absorbers
-
Ingår i: Progress in Photovoltaics. - 1062-7995 .- 1099-159X.
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we assessed the potential of KF-Post Deposition Treatment (PDT) performed on a silver-alloyed Cu(Inx,Ga1-x)Se2 (ACIGS) solar absorber. ACIGS absorbers with Ag/Ag+Cu ratio (Ag/I) close to 20% were co-evaporated on a Mo-coated glass substrate and exposed to in-situ KF-PDT of various intensities. The current-voltage characteristics indicated that an optimized PDT can be beneficial, increasing in our study the median Voc and efficiency values by +48 mV and +0.9 %abs (from 728 mV and 16.1 % efficiency measured for the sample without PDT), respectively. However, an increased KF-flux during PDT resulted in a net deterioration of the performance leading to median Voc and efficiency values as low as 503 mV and 4.7 %. The chemical composition analysis showed that while the reference absorber without any PDT was homogeneous, the KF-PDT induced a clear change within the first 10 nm from the surface. Here, the surface layer composition was richer in K and In with an increased Ag/I ratio, and its thickness seemed to follow the KF exposure intensity. Additionally, high-dose KF-PDT resulted in substantial formation of secondary phases for the ACIGS. The secondary phase precipitates were also richer in Ag, K and In, and Electron and X-ray diffraction data match with the monoclinic C 1 2/c 1 space group adopted by the Ag-alloyed KInSe2 (AKIS) phase. It could not be concluded whether the performance loss for the solar cell devices originated from the thicker surface layer or the presence of secondary phases, or both for the high-dose KF-PDT sample.
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| 14. |
- Edoff, Marika, 1965-, et al.
(författare)
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Post Deposition Treatments of (Ag,Cu)(In,Ga)Se-2 Thin Films for Solar Cells
- 2019
-
Ingår i: 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC). - New York : IEEE. - 9781728104942 ; , s. 618-621
-
Konferensbidrag (refereegranskat)abstract
- Different alkali alternatives for post-deposition of ACIGS were tested, both conventional fluoride salts and in the form of metals. XPS analysis of surfaces treated with K or KF as well as Rb or RbF have been performed, before (only for K and Rb) and after an ammonia etch. In addition to a strong suppression of Cu and Ag near the surface, we observe a difference in the re-distribution of Ga in the surface region after the etch depending on pdt element. Our results are consistent with the formation of K-In-Se and Rb-In-Se compounds for both metal alkalis and alkali fluorides. We find a similar beneficial effect on cell performance for the best cells with the metals as with the fluoride salts.
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| 15. |
- Ericson, Tove, 1983-, et al.
(författare)
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Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells
- 2013
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 535, s. 22-26
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Tidskriftsartikel (refereegranskat)abstract
- Reactively sputtered Cu–Zn–Sn–S precursor films are prepared and recrystallized by rapid thermal processing to generate Cu2ZnSnS4 solar cell absorber layers. We study how the film properties are affected by substrate heating and composition. The stress, density and texture in the films were measured. Compressive stress was observed for the precursors but did not correlate to the deposition temperature, and had no influence on the properties of the annealed films or solar cells. However, the substrate temperature during precursor deposition had a large effect on the behavior during annealing and on the solar cell performance. The films deposited at room temperature had, after annealing, smaller grains and cracks, and gave shunted devices. Cracking is suggested to be due to a slightly higher sulfur content, lower density or to minor differences in material quality. The grain size in the annealed films seems to increase with higher copper content and higher precursor deposition temperature. The best device in the current series gave an efficiency of 4.5%.
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| 16. |
- Ericson, Tove, 1983-, et al.
(författare)
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Zinc-Tin-Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd-Free Cu2ZnSnS4 Solar Cell
- 2017
-
Ingår i: Solar RRL. - : Wiley. - 2367-198X. ; 1:5
-
Tidskriftsartikel (refereegranskat)abstract
- Zn1−xSnxOy (ZTO) has yielded promising results as a buffer material for the full sulfur Cu2ZnSnS4 (CZTS), with efficiencies continuously surpassing its CdS-references. ZTO can be deposited by atomic layer deposition (ALD), enabling tuning of the conduction band position through the choice of metal ratio or deposition temperature. Thus, an optimization of the conduction band alignment between ZTO and CZTS can be achieved. The ZTO bandgap is generally larger than that of CdS and can therefore yield higher currents due to reduced losses in the short wavelength region. Another advantage is the possibility to omit the toxic Cd. In this study, the ALD process temperature was varied from 105 to 165 °C. Current-blocked devices were obtained at 105 °C, while the highest open-circuit voltage and device efficiency was achieved for 145 °C. The highest fill factor was seen at 165 °C. The best efficiency reached in this study was 9.0%, which, to our knowledge, is the highest efficiency reported for Cd-free full-sulfur CZTS. We also show that the effect of heat needs to be taken into account. The results indicate that part of the device improvement comes from heating the absorber, but that the benefit of using a ZTO-buffer is clear.
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| 17. |
- Ericson, Tove, 1983-, et al.
(författare)
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Zn(O,S) Buffer Layers and Thickness Variations of CdS Buffer for Cu2ZnSnS4 Solar Cells
- 2014
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381. ; 4:1, s. 465-469
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Tidskriftsartikel (refereegranskat)abstract
- To improve the conduction band alignment and explore the influence of the buffer-absorber interface, we here investigate an alternative buffer for Cu2ZnSnS4 (CZTS) solar cells. The Zn(O, S) system was chosen since the optimum conduction band alignment with CZTS is predicted to be achievable, by varying oxygen to sulfur ratio. Several sulfur to oxygen ratios were evaluated to find an appropriate conduction band offset. There is a clear trend in open-circuit voltage Voc, with the highest values for the most sulfur rich buffer, before going to the blocking ZnS, whereas the fill factor peaks at a lower S content. The best alternative buffer cell in this series had an efficiency of 4.6% and the best CdS reference gave 7.3%. Extrapolating Voc values to 0 K gave activation energies well below the expected bandgap of 1.5 eV for CZTS, which indicate that recombination at the interface is dominating. However, it is clear that the values are affected by the change of buffer composition and that increasing sulfur content of the Zn(O, S) increases the activation energy for recombination. A series with varying CdS buffer thickness showed the expected behavior for short wavelengths in quantum efficiency measurements but the final variation in efficiency was small.
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| 18. |
- Frisk, Christopher, 1985-, et al.
(författare)
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On the extraction of doping concentration from capacitance-voltage : A Cu2ZnSnS4 and ZnS sandwich structure
- 2017
-
Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 7:5, s. 1421-1425
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Tidskriftsartikel (refereegranskat)abstract
- The capacitance-voltage (C-V) method is frequently used to evaluate the net doping of thin-film solar cells, an important parameter for the function of solar cells. However, complex materials such as kesterites are challenging to characterize. To minimize ambiguity when determining the apparent doping concentration (N-A) of Cu2ZnSnS4 (CZTS), we fabricated and investigated different structures: CZTS/ZnS metal-insulator-semiconductor (MIS) device, stand-alone CZTS and ZnS metal-sandwich structures, and CZTS solar cells. Characterization was carried out by means of admittance spectroscopy (AS) and C-V measurements. ZnS exhibits excellent intrinsic properties, and with the high-quality MIS sample we managed to successfully isolate the capacitive response of the CZTS itself. N-A, as extracted from the MIS structure, is found to be more reliable and four times higher compared with the solar cell, impacting any estimated collection efficiency substantially. Data herein presented also show that CZTS has a substantial low-frequency dispersive capacitance and the extraction of N-A depends on the chosen measurement frequency, symptoms of presence of deep defects. Furthermore, the CZTS/ZnS MIS structure is strongly resilient to leakage currents at both forward and reverse voltage bias where contribution from deep defects is minimized and maximized, respectively.
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| 19. |
- Gerdin Hulkko, Johan, 1986-
(författare)
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Muspel and Surtr : CVD system and control program for WF6 chemistry
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- CVD (Chemical Vapour Deposition) is an advanced technique for depositing a coating on a substrate. CVD implies that a solid phase is deposited on a normally heated substrate surface using a reactive, gaseous mixture. The reaction gas mixture must be carefully chosen to prevent homogeneous nucleation in the gas phase. As the solid phase is formed, gaseous by-products are formed and they must be removed from the CVD system. The thermally activated CVD process requires a deposition system which can regulate the total pressure and mass flows of the separate gas components as well as maintain a sufficiently high temperature to initiate a chemical reaction on the substrate surface.In this thesis a new CVD system was constructed to meet these challenges. Initially it will be used to deposit hard, wear resistant coatings but by changing the gases, it is possible to explore other chemical systems. The CVD system functions well up to a deposition temperature of 1100 ºC as long as the CVD processes are thermally activated. Apart from manual operation, a LabView control interface was implemented that can automate process steps by reading recipe files as csv (comma-separated variables). In this way complex coating architectures can be deposited.The aim of this thesis is to give a detailed description of the hardware set-up and of the software developed for it. Provided in this work are also a few examples of W and WN (tungsten nitride) coatings, including a multi-layered structure to show the potential of complex structures. Since the system also contains a titanium precursor, a TiN (titanium nitride) coating is presented to conceptually show the flexibility of the equipment.
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| 20. |
- Holmqvist, Anders, et al.
(författare)
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A model-based methodology for the analysis and design of atomic layer deposition processes-Part III : Constrained multi-objective optimization
- 2013
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 96, s. 71-86
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a structured methodology for the constrained multi-objective optimization (MO) of a continuous cross-flow atomic layer deposition (ALD) reactor model with temporal precursor pulsing. The process model has been elaborated and experimentally validated in the first two papers of this series (33 and 34). A general constrained MO problem (MOP) was formulated to simultaneously optimize quasi-steady-state reactor throughput and overall precursor conversion for the controlled deposition of ZnO films from Zn(C2H5)(2) and H2O, subject to a set of operational constraints. These constraints included lower bounds for the cross-substrate film thickness uniformity and post-precursor purge duration. The non-dominated Pareto optimal solutions obtained successfully revealed the relation between the incommensurable process objectives and reduced the design space of the ALD process into a feasible set of design alternatives. The results presented here show that post-precursor purge duration is essential when optimizing throughput in temporally separated ALD processes, and that this is a major drawback when considering operation at atmospheric pressure. Finally, the robustness of the process along the Pareto optimal front, i.e. the ability of the process to accommodate variations in the associated set of optimal decision variables (DVs), was assessed by Monte Carlo simulations, in which the values of the parametric uncertainties were randomly generated from a multivariate normal distribution. The uncertainty and sensitivity analysis showed that the inherent robustness of the process is progressively lost with the precursor conversion, and revealed the mechanistic dependence of all DVs on the proposed optimization specifications.
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| 21. |
- Holmqvist, Anders, et al.
(författare)
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A model-based methodology for the analysis and design of atomic layer deposition processes—Part I : Mechanistic modelling of continuous flow reactors
- 2012
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 81, s. 260-272
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the development of an experimentally validated model that mechanistically comprehends the complex interaction between the gas-phase fluid dynamics, the mass transport of individual species, and the heterogeneous gas–surface reaction mechanism in a continuous cross-flow atomic layer deposition (ALD) reactor. The developed ALD gas–surface reaction mechanism, purely based on consecutive and parallel elementary Eley–Rideal reaction steps, was incorporated into the computational fluid dynamic representation of the equipment-scale. Thereby, the model mechanistically relates local gas-phase conditions in the vicinity of the substrate surface to the transient production and consumption of the fractional surface coverage of chemisorbed species, ultimately underlying epitaxial film growth. The model is oriented towards optimization and control and enables identification of substrate film thickness uniformity sensitivities to process operating parameters, reactor system design and gas flow distribution. For the experimental validation of the derived mathematical model, a detailed experimental investigation with the focus on the impact of process operating parameters on the spatial evolution of ZnO film thickness profile was performed. The controlled deposition of ZnO from Zn(C2H5)2 and H2O was carried out in the continuous cross-flow ALD reactor system F-120 by ASM Microchemistry Ltd. and ex situ film thickness measurements at a discrete set of sampling positions on the substrate were performed using X-ray reflectivity and X-ray fluorescence analysis. The experimental results reported here, underscore the importance of substrate-scale uniformity measurements in developing mechanistic ALD process models with high predictability of the dynamic evolution of the spatially dependent film thickness profile. The experimental validation and extensive mechanistic analysis of the ALD reactor model are presented in the second article of this series.
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| 22. |
- Holmqvist, Anders, et al.
(författare)
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A model-based methodology for the analysis and design of atomic layer deposition processes—Part II : Experimental validation and mechanistic analysis
- 2013
-
Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 94, s. 316-329
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates the experimental validation and mechanistic analysis of the continuous cross-flow atomic layer deposition (ALD) reactor model developed in the first article of this series (Holmqvist et al., in press). A general nonlinear parameter estimation problem was formulated to identify the kinetic parameters involved in the developed ALD gas–surface reaction mechanism, governing ZnO film growth, from ex situ film thickness measurements. The presented methodology for comprehensive model assessment considers the statistical uncertainty of least-squares estimates and its ultimate impact on the model predicted response. Joint inference regions were determined to assess the significance of parameter estimates and results indicate that all estimates involved in the precursor half-reactions were adequately determined. The reparameterization of the Arrhenius equation effectively decreased the characteristically high correlations between Arrhenius parameters, leading to improvement in precision of individual parameter estimates. Model predictions of the spatially dependent film thickness profile with narrow confidence band were in good agreement with both calibration and validation experimental data, respectively, under a wide range of operating conditions. The subsequent extensive theoretical analysis exhibits that the experimentally validated model successfully reproduces the detailed process dynamics revealed by in situ quartz crystal microbalance and quadrupole mass spectroscopy diagnostics, and thereby provides a supplementary analysis tool. Finally, the univariate sensitivity analysis revealed the mechanistic dependence of all the measured process operating parameters on the spatially dependent film thickness profile, resolved at the level of a single pulse sequence. Hence, the presented model-based framework serves as a means to guide future research efforts in the field of ALD process optimization.
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| 23. |
- Holmqvist, Anders, et al.
(författare)
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Dynamic parameter estimation of atomic layer deposition kinetics applied to in situ quartz crystal microbalance diagnostics
- 2014
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 111, s. 15-33
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the elaboration of an experimentally validated model of a continuous cross flow atomic layer deposition (ALD) reactor with temporally separated precursor pulsing encoded in the Moclelica language. For the experimental validation of the model, in situ quartz crystal microbalance (QCM) diagnostics was used to yield submonolayer resolution of mass deposition resulting from thin film growth of ZnO from Zn(C-2)(2) and H2O precursors. The ZnO ALD reaction intrinsic kinetic mechanism that was developed accounted for the temporal evolution of the equilibrium fractional surface concentrations of precursor adducts and their transition states for each half reaction, This mechanism was incorporated into a rigorous model of reactor transport, which comprises isothermal compressible equations for the conservation of mass, momentum and gas-phase species. The physically based model in this way relates the local partial pressures of precursors to the dynamic composition of the growth surface, and ultimately governs the accumulated mass trajectory at the QCM sensor. Quantitative rate information can then be extracted by means of dynamic parameter estimation. The continuous operation of the reactor is described by limit-cycle dynamic solutions and numerically computed using Radau collocation schemes and solved using CasADi's interface to [PORT. Model predictions of the transient mass gain per unit area of exposed surface QCM sensor, resolved at a single pulse sequence, were in good agreement with experimental data under a wide range of operating conditions. An important property of the limit-cycle solution procedure is that it enables the systematic approach to analyze the dynamic nature of the growth surface composition as a function of process operating parameters. Especially, the dependency of the film growth rate per limit-cycle on the half-cycle precursor exposure close and the process temperature was thoroughly assessed and the difference between ALD in saturating and in non-saturating film growth conditions distinguished. (c) 2014 Elsevier Ltd. All rights reserved.
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| 24. |
- Hultqvist, Adam, et al.
(författare)
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Atomic Layer Deposition of Electron Selective SnOx and ZnO Films on Mixed Halide Perovskite : Compatibility and Performance
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:35, s. 29707-29716
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Tidskriftsartikel (refereegranskat)abstract
- The compatibility of atomic layer deposition directly onto the mixed halide perovskite formamidinium lead iodide:methylammonium lead bromide (CH(NH2)(2), CH3NH3)Pb(I,Br)(3) (FAPbI(3):MAPbBr(3)) perovskite films is investigated by exposing the perovskite films to the full or partial atomic layer deposition processes for the electron selective layer candidates ZnO and SnOx. Exposing the samples to the heat, the vacuum, and even the counter reactant of H2O of the atomic layer deposition processes does not appear to alter the perovskite films in terms of crystallinity, but the choice of metal precursor is found to be critical. The Zn precursor Zn(C2H5)(2) either by itself or in combination with H2O during the ZnO atomic layer deposition (ALD) process is found to enhance the decomposition of the bulk of the perovskite film into PbI2 without even forming ZnO. In contrast, the Sn precursor Sn(N(CH3)(2))(4) does not seem to degrade the bulk of the perovskite film, and conformal SnOx films can successfully be grown on top of it using atomic layer deposition. Using this SnOx film as the electron selective layer in inverted perovskite solar cells results in a lower power conversion efficiency of 3.4% than the 8.4% for the reference devices using phenyl-C-70-butyric acid methyl ester. However, the devices with SnOx show strong hysteresis and can be pushed to an efficiency of 7.8% after biasing treatments. Still, these cells lacks both open circuit voltage and fill factor compared to the references, especially when thicker SnOx films are used. Upon further investigation, a possible cause of these losses could be that the perovskite/SnOx interface is not ideal and more specifically found to be rich in Sn, O, and halides, which is probably a result of the nucleation during the SnOx growth and which might introduce barriers or alter the band alignment for the transport of charge carriers.
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| 25. |
- Hultqvist, Adam
(författare)
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Cadmium Free Buffer Layers and the Influence of their Material Properties on the Performance of Cu(In,Ga)Se2 Solar Cells
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- CdS is conventionally used as a buffer layer in Cu(In,Ga)Se2, CIGS, solar cells. The aim of this thesis is to substitute CdS with cadmium-free, more transparent and environmentally benign alternative buffer layers and to analyze how the material properties of alternative layers affect the solar cell performance. The alternative buffer layers have been deposited using Atomic Layer Deposition, ALD. A theoretical explanation for the success of CdS is that its conduction band, Ec, forms a small positive offset with that of CIGS. In one of the studies in this thesis the theory is tested experimentally by changing both the Ec position of the CIGS and of Zn(O,S) buffer layers through changing their gallium and sulfur contents respectively. Surprisingly, the top performing solar cells for all gallium contents have Zn(O,S) buffer layers with the same sulfur content and properties in spite of predicted unfavorable Ec offsets. An explanation is proposed based on observed non-homogenous composition in the buffer layer. This thesis also shows that the solar cell performance is strongly related to the resistivity of alternative buffer layers made of (Zn,Mg)O. A tentative explanation is that a high resistivity reduces the influence of shunt paths at the buffer layer/absorber interface. For devices in operation however, it seems beneficial to induce persistent photoconductivity, by light soaking, which can reduce the effective Ec barrier at the interface and thereby improve the fill factor of the solar cells. Zn-Sn-O is introduced as a new buffer layer in this thesis. The initial studies show that solar cells with Zn-Sn-O buffer layers have comparable performance to the CdS reference devices. While an intrinsic ZnO layer is required for a high reproducibility and performance of solar cells with CdS buffer layers it is shown in this thesis that it can be thinned if Zn(O,S) or omitted if (Zn,Mg)O buffer layers are used instead. As a result, a top conversion efficiency of 18.1 % was achieved with an (Zn,Mg)O buffer layer, a record for a cadmium and sulfur free CIGS solar cell.
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