CIS/CIGS PHOTOVOLTAICS
Development of CIS/CIGS Thin Film Solar Cells by
Chemical and Electrochemical THIN FILM GROWTH and
CHARACTERIZATION of
CIS/CIGS Photovoltaic Absorber, ZnSe-buffer, and Al:ZnO/ZnO-window

Ρούπακας, Γεώργιος; Roupakas, Georgios

dc.contributor.author	Ρούπακας, Γεώργιος	el
dc.contributor.author	Roupakas, Georgios	en
dc.date.accessioned	2024-09-12T09:06:11Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/60207
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.27903
dc.rights	Αναφορά Δημιουργού 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by/3.0/gr/	*
dc.subject	Chalcopyrite thin films	en
dc.subject	ECD growth
dc.subject
dc.subject
dc.subject	Ηλεκτροχημική εναπόθεση
dc.subject	Λεπτά υμένια χαλκοπυριτών
dc.subject
dc.subject
dc.subject
dc.title	CIS/CIGS PHOTOVOLTAICS Development of CIS/CIGS Thin Film Solar Cells by Chemical and Electrochemical THIN FILM GROWTH and CHARACTERIZATION of CIS/CIGS Photovoltaic Absorber, ZnSe-buffer, and Al:ZnO/ZnO-window	en
heal.type	doctoralThesis
heal.generalDescription	CIS/CIGS PHOTOVOLTAICS	el
heal.classification	Applied Physics	en
heal.dateAvailable	2025-09-11T21:00:00Z
heal.language	en
heal.access	embargo
heal.recordProvider	ntua	el
heal.publicationDate	2024-06
heal.abstract	Overall application of inexpensive, non-vacuum chemical (CBD) and electrochemical deposition (ECD) techniques that can be scaled-up to industrial processes is targeted for processing the absorber-, buffer-, and window-layer of CISe/CIGSe TFSCs to overcome current process incompatibilities mainly resulting from the simultaneous use of moderate temperature non-vacuum (50-70 oC) and high temperature (500-700 oC) vacuum processes. Low cost ECD processing of ternary CuInSe2 and quaternary Cu(In,Ga)Se2 chalcopyrite semiconductor films with crystal quality similar to that of PVD grown films was achieved by as few as possible process steps skipping selenization at elevated temperatures. Chalcopyrite phase formation was confirmed already in as-deposited films. The film quality was further improved by subsequent annealing at 300oC, for 2h, in N2. ZnSe buffer- and ZnO window-layers were processed by CBD and ECD techniques, respectively. The properties of n-ZnO/i-ZnO bilayer were thoroughly investigated with respect to layer thickness and dopant concentration. By successive integration of low cost ECD-ZnO/CBD-ZnSe buffer and window components in CISe/CIGSe solar cells with absorbers grown by standard vacuum techniques, the respective p-n junctions exhibited I-V characteristics competing with those of monocrystalline silicon (c-Si) I(V). Ternary CuInSe2 and quaternary Cu(In,Ga)Se2 chalcopyrite semiconductor films with potential applications as solar absorbers were deposited by single-step electrochemical deposition (ECD) on molybdenum coated glass substrates. The films have been structurally characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy dispersive x-ray analysis (EDAX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Chalcopyrite phase formation was confirmed already in as-deposited films. The crystal structure of the films was further improved by thermal treatment. Element interdiffusion at the chalcopyrite/Mo/glass interface has been prevented by retaining moderate temperatures of deposition (70 °C) and subsequent annealing (300 °C). The SEM/EDAX analysis revealed the presence of CuxSe secondary phases on the surface of ternary films and almost stoichiometric growth of quaternary deposited on top of ternary films. The XRD and Raman analysis confirmed the high quality assessment of the films being almost equal to that of chalcopyrite selenide layers grown by physical vapor deposition at high temperatures (550-750 °C). The surface sensitive XPS analysis confirmed the absence of other impurities in the ECD processed films except from oxygen and carbon adsorbents by sample exposure to atmospheric air. ZnSe thin films were initially deposited by electron-beam evaporation techniques (EBE) on amorphous glass substrates at temperatures ranging from room temperature (RT) to 450 oC. The films were structurally and optically characterized by X-Ray Diffraction (XRD), Energy Dispersive X-Ray Analysis (EDAX), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Raman spectroscopy, and Null-Ellipsometry. XRD Diffractograms revealed cubic structure (fcc) with preferential orientation along the [111]-direction of growth. Plane spacing d and lattice constant a were calculated from the Bragg-angles. SEM and AFM images demonstrated highly homogenous polycrystalline structure and smooth film surfaces. Compositional analysis by EDAX indicated formation of non-stoichiometric Zn-poor films becoming more stoichiometric with the increase of deposition temperature. The Raman LO-phonon width (FWHM) used to calculate crystallite sizes results in size increase with the increase of deposition temperature. Refractive index n=2.586, absorption coefficient α=1.9x103 cm-1, and film thickness d=100-110 nm obtained by Null-Ellipsometry at 546 nm show weak temperature dependence only in case of absorption. According to the results of the structural and optical characterization, ZnSe thin films deposited by EBE on amorphous glass substrates at room and moderate substrate temperatures (< 100 oC) have good crystallinity that can be further improved with the increase of deposition temperature up to 450 oC. Based on the results of good quality ZnSe films grown on (amorphous) glass substrates, high quality ZnSe thin films were deposited by electron-beam evaporation techniques (EBE) on CuGaSe2 (CGS) absorbers used in solar-cell device development. The deposited films act as buffer layers in heterojunction CGS based cells. Film deposition took place at 400 oC. The films were subjected to post-growth annealing and were structurally and optically characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Raman Spectroscopy, Null-Ellipsometry, and room temperature (RT) Photoreflectance Spectroscopy (PR). X-Ray Diffractograms revealed (fcc) zinc-blende structure with preferential orientation along the (111) direction of growth. SEM and AFM images demonstrated films with highly homogenous structure and small surface roughness. The average grain size was found to be in the order of 100 nm. Raman spectra confirmed the good crystal quality of the films. Null-Ellipsometry measurements yielded values of n=2.580 and α=6.2x103 cm-1 for the refractive index and the absorption coefficient of the films at 546 nm excitation wavelength, respectively. The film thickness deduced from the Ellipsometry measurements was d=80 nm. The energy band-gap of the films was obtained by room temperature (RT) Photoreflectance (PR) to Eg= 2.69 eV. The application of PR spectroscopy at RT along with the results of SEM, AFM, XRD, and Raman spectroscopy confirm the excellent crystal quality of the deposited films. Aiming to overall cost-effective chalcopyrite solar cell processing by wet-processing techniques, Chemical Bath Deposition (CBD) was also probed as preparation technique of the buffer-layer in addition to the in-vacuum Evaporation by electron-beam (EBE). Good quality ZnSe layers were deposited from zinc-sulfate (ZnSO4) chemical solution bath containing selenourea (SeC(NH2)2), ammonia (NH3), hydrazine (NH2NH2), and sodiumsulfite (Na2SO3) precursors. The layers were characterized structurally by XRD, SEM, AFM, and optically by absorption spectroscopy. The optimization of the deposition parameters of CBD deposited ZnSe buffer-layer is handled in the PhD-thesis of NTUA Dipl. Appl. Phys. K. Anestou supervised also by Prof. Dr. D. Ν. Papadimitriou. High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the (1011) crystallographic direction from aqueous solution of zinc nitrate (Zn(NO3)2) at negative electrochemical potential of EC= (-0.8) - (-1.2) V and moderate temperature of 80 °C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se2 (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se2/Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy Eg of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ ~10-5 Ω.cm-1; the respective carrier concentration of the order 1022 cm-3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N2 flux regulation. The hydrostatic compressive strain due to Al3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl3 dopant was εh= -0.050 and the respective hydrostatic stress σh= -21 GPa. The surface reflectivity of maximum 5% over the scanned region of 180-900 nm and the (optical) band gap of Eg= 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD) Al:ZnO bilayers. By successive integration of low cost ECD ZnO/CBD ZnSe buffer and window components in CISe/CIGSe solar cells with absorbers grown by standard vacuum techniques, the respective p-n junctions exhibited I-V characteristics competing with those of monocrystalline silicon (c-Si) I(V).	en
heal.advisorName	Παπαδημητρίου, Δήμητρα	el
heal.advisorName	Papadimitriou, Dimitra
heal.committeeMemberName	Κοντός, Αθανάσιος	el
heal.committeeMemberName	Ζουμπουλάκης, Λουκάς	el
heal.committeeMemberName	Τσέτσερης, Λεωνίδας	el
heal.committeeMemberName	Μαρκάτος, Νικόλαος	el
heal.committeeMemberName	Χατζηθεοδωρίδης, Ηλίας	el
heal.committeeMemberName	Γεωργίου, Ιωάννης	el
heal.committeeMemberName	Παπαδημητρίου, Δήμητρα	el
heal.committeeMemberName	Kontos, Athanasios
heal.committeeMemberName	Zoumpoulakis, Loukas
heal.committeeMemberName
heal.committeeMemberName
heal.committeeMemberName
heal.committeeMemberName
heal.committeeMemberName
heal.committeeMemberName
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Εφαρμοσμένων Μαθηματικών και Φυσικών Επιστημών. Τομέας Φυσικής	el
heal.academicPublisherID	ntua
heal.numberOfPages	292
heal.fullTextAvailability	false