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Key Developments in Thin Film Solar Cells

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (15 January 2016) | Viewed by 48122

Special Issue Editor

Department of Physics and Earth Sciences “Macedonio Melloni”, The University of Parma, Parco Area delle Scienze, 7/a, 43124 - Parma - Italy
Interests: Technologies: photovoltaic solar cells and modules; thin film deposition; sputtering, vacuum thermal evaporation high (HVTE); close-spaced sublimation (CSS); electron-beam gun (EBG); laser scribing, monolithical integration. Materials: Cu(In,Ga)Se2 (CIGSe); CdTe, Cu2ZnSn(S,Se)4 (CZT(S,Se)); CdS; transparent conducting oxide (TCO); semiconducting material; metals; insulating materials Investigation techniques: atomic-force microscopy (AFM); scanning electron microscopy (SEM); energy-dispersive spectroscopy (EDS); transmission electron microscopy (TEM); X-ray diffraction (XRD); secondary ion mass spectroscopy (SIMS); μRaman; cathode- and photo-luminescence (CL and PL); electron beam induced current (EBIC), deep-level spestroscopy (DLTS), Hall effect, spectral response and external quantum efficiency (EQE), I-V and C-V characteristics.

Special Issue Information

Dear Colleagues,

The worldwide annual photovoltaic (PV) module production is growing exponentially, with an average yearly increase of the installed capacity of slightly higher than 30%. Nevertheless, the development of ultralow-cost PV systems, to ensure the economic viability of solar energy in terrestrial applications, is widely considered a necessary step in the near future. Thin-film solar cells, saving on raw materials and being environmentally friendly technologies, have the potential to meet this need. Moreover, thin films show advantages over their bulk-semiconductor counterparts due to their lighter weight, flexible shape, easier building integration, device fabrication schemes, and low cost in large-scale production. As evidence, several technologies have been implemented and different materials have proven their suitability for the production of solar cells in excess of 20% conversion efficiency. A keystone will be to continue and even intensify research in thin-film solar cells, in order to ensure viable options for a large-scale use of photovoltaic solar electricity. This Special Issue is a contribution towards this ambition. It will cover most possibilities for thin-film solar cells, which are presently being studied: thin-film silicon, polycrystalline and amorphous semiconductors (a-Si, Cu(In,Ga)Se2, CdTe, kesterites), organic photovoltaics (OPV), and dye-sensitized solar cells (DSSC). Moreover, it presents a wide range of scientific and technological aspects on deposition technologies, basic properties, and device physics of high-efficiency thin film solar cells.

We invite investigators to contribute original research articles, as well as review articles, that will stimulate the continuing efforts to understand the best strategies for developing high efficiency solar cells.

Dr. Prof. Alessio Bosio
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • solar cell
  • thin film technology
  • calchogenides, CdTe, CdS
  • chalcopyrites, CIGS
  • kesterites, CZTS
  • silicon thin-film solar cells
  • dye-sensitized solar cells, DSSC
  • organic photovoltaics, OPV
  • high efficiency
  • large-area modules

Published Papers (9 papers)

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Research

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2114 KiB  
Article
Multi-Objective Optimization of Thin-Film Silicon Solar Cells with Metallic and Dielectric Nanoparticles
by Giovanni Aiello, Salvatore Alfonzetti, Santi Agatino Rizzo and Nunzio Salerno
Energies 2017, 10(1), 53; https://doi.org/10.3390/en10010053 - 04 Jan 2017
Cited by 4 | Viewed by 3493
Abstract
Thin-film solar cells enable a strong reduction of the amount of silicon needed to produce photovoltaic panels but their efficiency lowers. Placing metallic or dielectric nanoparticles over the silicon substrate increases the light trapping into the panel thanks to the plasmonic scattering from [...] Read more.
Thin-film solar cells enable a strong reduction of the amount of silicon needed to produce photovoltaic panels but their efficiency lowers. Placing metallic or dielectric nanoparticles over the silicon substrate increases the light trapping into the panel thanks to the plasmonic scattering from nanoparticles at the surface of the cell. The goal of this paper is to optimize the geometry of a thin-film solar cell with silver and silica nanoparticles in order to improve its efficiency, taking into account the amount of silver. An efficient evolutionary algorithm is applied to perform the optimization with a reduced computing time. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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1701 KiB  
Article
Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells
by Yu-Tsu Lee, Fang-Ru Lin, Ting-Chun Lin, Chien-Hsun Chen and Zingway Pei
Energies 2016, 9(6), 402; https://doi.org/10.3390/en9060402 - 25 May 2016
Cited by 8 | Viewed by 5529
Abstract
In this paper, we propose a chemically grown titanium oxide (TiO2) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO2 does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A [...] Read more.
In this paper, we propose a chemically grown titanium oxide (TiO2) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO2 does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO2/Si interface was observed. X-ray photoemission spectroscopy (XPS) revealed that the chemically grown TiO2 is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT) model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 105 orders of magnitude higher for holes passing through TiO2 than for flow through SiO2. With 24-nm-thick TiO2, a Si solar cell achieves a 33.2 mA/cm2 photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO2 deposition. This structure enables light harvesting for a high photocurrent. The high photocurrent and ease of production of chemically grown TiO2 imply that it is a suitable candidate for future low-cost, high-efficiency solar cell applications. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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3811 KiB  
Article
How the Chlorine Treatment and the Stoichiometry Influences the Grain Boundary Passivation in Polycrystalline CdTe Thin Films
by Alessio Bosio, Greta Rosa, Daniele Menossi and Nicola Romeo
Energies 2016, 9(4), 254; https://doi.org/10.3390/en9040254 - 31 Mar 2016
Cited by 15 | Viewed by 5191
Abstract
The absorption coefficient of CdTe is large enough to assure that all of the visible light is absorbed in a thickness on the order of 1 µm. High efficiency devices are fabricated by using close-spaced sublimation (CSS)-deposited CdTe films with a thickness in [...] Read more.
The absorption coefficient of CdTe is large enough to assure that all of the visible light is absorbed in a thickness on the order of 1 µm. High efficiency devices are fabricated by using close-spaced sublimation (CSS)-deposited CdTe films with a thickness in the range of 6–8 µm. In order to decrease the thickness of the CdTe film, a novel approach has been used. On top of the CdTe film, whose thickness is reduced to 2–3 μm, another CdTe layer is deposited by RF sputtering, with a thickness of 100–200 nm. The purpose of this approach is to fill up the voids, which tend to form when a low thickness-CdTe film is deposited by close-spaced sublimation. Using this CdTe double layer, solar cells, with an efficiency greater than 15%, were reproducibly obtained. Since the CdTe layer deposited by the CSS technique shows a p-type behavior, whereas the layer deposited by sputtering is n-type, it is supposed that the formation of a p-n junction into the grain boundaries, which makes a mirror for the charge carriers, increases their mean lifetime. In order to also have this system after the essential chlorine treatment of the CdTe layer, a special cadmium-free halogen treatment was developed. This process was especially tuned for very thin (≤3 µm) CdTe film thickness and for not making use of cadmium-based chlorine salt while, producing high efficiency devices, meets a better economic and environmental sustainability. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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3679 KiB  
Article
Advances in Thin-Film Si Solar Cells by Means of SiOx Alloys
by Lucia V. Mercaldo, Iurie Usatii and Paola Delli Veneri
Energies 2016, 9(3), 218; https://doi.org/10.3390/en9030218 - 18 Mar 2016
Cited by 12 | Viewed by 4991
Abstract
The conversion efficiency of thin-film silicon solar cells needs to be improved to be competitive with respect to other technologies. For a more efficient use of light across the solar spectrum, multi-junction architectures are being considered. Light-management considerations are also crucial in order [...] Read more.
The conversion efficiency of thin-film silicon solar cells needs to be improved to be competitive with respect to other technologies. For a more efficient use of light across the solar spectrum, multi-junction architectures are being considered. Light-management considerations are also crucial in order to maximize light absorption in the active regions with a minimum of parasitic optical losses in the supportive layers. Intrinsic and doped silicon oxide alloys can be advantageously applied within thin-film Si solar cells for these purposes. Intrinsic a-SiOx:H films have been fabricated and characterized as a promising wide gap absorber for application in triple-junction solar cells. Single-junction test devices with open circuit voltage up to 950 mV and ~1 V have been demonstrated, in case of rough and flat front electrodes, respectively. Doped silicon oxide alloys with mixed-phase structure have been developed, characterized by considerably lower absorption and refractive index with respect to standard Si-based films, accompanied by electrical conductivity above 10−5 S/cm. These layers have been successfully applied both into single-junction and micromorph tandem solar cells as superior doped layers with additional functionalities. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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3437 KiB  
Article
Progress on Low-Temperature Pulsed Electron Deposition of CuInGaSe2 Solar Cells
by Massimo Mazzer, Stefano Rampino, Enos Gombia, Matteo Bronzoni, Francesco Bissoli, Francesco Pattini, Marco Calicchio, Aldo Kingma, Filippo Annoni, Davide Calestani, Nicholas Cavallari, Vimalkumar Thottapurath Vijayan, Mauro Lomascolo, Arianna Cretì and Edmondo Gilioli
Energies 2016, 9(3), 207; https://doi.org/10.3390/en9030207 - 16 Mar 2016
Cited by 22 | Viewed by 6917
Abstract
The quest for single-stage deposition of CuInGaSe2 (CIGS) is an open race to replace very effective but capital intensive thin film solar cell manufacturing processes like multiple-stage coevaporation or sputtering combined with high pressure selenisation treatments. In this paper the most recent [...] Read more.
The quest for single-stage deposition of CuInGaSe2 (CIGS) is an open race to replace very effective but capital intensive thin film solar cell manufacturing processes like multiple-stage coevaporation or sputtering combined with high pressure selenisation treatments. In this paper the most recent achievements of Low Temperature Pulsed Electron Deposition (LTPED), a novel single stage deposition process by which CIGS can be deposited at 250 °C, are presented and discussed. We show that selenium loss during the film deposition is not a problem with LTPED as good crystalline films are formed very close to the melting temperature of selenium. The mechanism of formation of good ohmic contacts between CIGS and Mo in the absence of any MoSe2 transition layers is also illustrated, followed by a brief summary of the measured characteristics of test solar cells grown by LTPED. The 17% efficiency target achieved by lab-scale CIGS devices without bandgap modulation, antireflection coating or K-doping is considered to be a crucial milestone along the path to the industrial scale-up of LTPED. The paper ends with a brief review of the open scientific and technological issues related to the scale-up and the possible future applications of the new technology. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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1325 KiB  
Article
Intermittent Very High Frequency Plasma Deposition on Microcrystalline Silicon Solar Cells Enabling High Conversion Efficiency
by Mitsuoki Hishida, Takeyuki Sekimoto, Mitsuhiro Matsumoto and Akira Terakawa
Energies 2016, 9(1), 42; https://doi.org/10.3390/en9010042 - 13 Jan 2016
Cited by 2 | Viewed by 4585
Abstract
Stopping the plasma-enhanced chemical vapor deposition (PECVD) once and maintaining the film in a vacuum for 30 s were performed. This was done several times during the formation of a film of i-layer microcrystalline silicon (μc-Si:H) used in thin-film silicon tandem solar cells. [...] Read more.
Stopping the plasma-enhanced chemical vapor deposition (PECVD) once and maintaining the film in a vacuum for 30 s were performed. This was done several times during the formation of a film of i-layer microcrystalline silicon (μc-Si:H) used in thin-film silicon tandem solar cells. This process aimed to reduce defect regions which occur due to collision with neighboring grains as the film becomes thicker. As a result, high crystallinity (Xc) of μc-Si:H was obtained. Eventually, a solar cell using this process improved the conversion efficiency by 1.3% (0.14 points), compared with a normal-condition cell. In this paper, we propose an easy method to improve the conversion efficiency with PECVD. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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2176 KiB  
Article
Electro-Plating and Characterisation of CdTe Thin Films Using CdCl2 as the Cadmium Source
by Nor A. Abdul-Manaf, Hussein I. Salim, Mohammad L. Madugu, Olajide I. Olusola and Imyhamy M. Dharmadasa
Energies 2015, 8(10), 10883-10903; https://doi.org/10.3390/en81010883 - 29 Sep 2015
Cited by 32 | Viewed by 6677
Abstract
Cadmium telluride (CdTe) thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2)·H2O and tellurium dioxide (TeO2) using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films [...] Read more.
Cadmium telluride (CdTe) thin films have been successfully prepared from an aqueous electrolyte bath containing cadmium chloride (CdCl2)·H2O and tellurium dioxide (TeO2) using an electrodeposition technique. The structural, electrical, morphological and optical properties of these thin films have been characterised using X-ray diffraction (XRD), Raman spectroscopy, optical profilometry, DC current-voltage (I-V) measurements, photoelectrochemical (PEC) cell measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-Vis spectrophotometry. It is observed that the best cathodic potential is 698 mV with respect to standard calomel electrode (SCE) in a three electrode system. Structural analysis using XRD shows polycrystalline crystal structure in the as-deposited CdTe thin films and the peaks intensity increase after CdCl2 treatment. PEC cell measurements show the possibility of growing p-, i- and n-type CdTe layers by varying the growth potential during electrodeposition. The electrical resistivity of the as-deposited layers are in the order of 104 Ω·cm. SEM and AFM show that the CdCl2 treated samples are more roughness and have larger grain size when compared to CdTe grown by CdSO4 precursor. Results obtained from the optical absorption reveal that the bandgap of as-deposited CdTe (1.48–1.52) eV reduce to (1.45–1.49) eV after CdCl2 treatment. Full characterisation of this material is providing new information on crucial CdCl2 treatment of CdTe thin films due to its built-in CdCl2 treatment during the material growth. The work is progressing to fabricate solar cells with this material and compare with CdTe thin films grown by conventional sulphate precursors. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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Review

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9671 KiB  
Review
How the Starting Precursor Influences the Properties of Polycrystalline CuInGaSe2 Thin Films Prepared by Sputtering and Selenization
by Greta Rosa, Alessio Bosio, Daniele Menossi and Nicola Romeo
Energies 2016, 9(5), 354; https://doi.org/10.3390/en9050354 - 10 May 2016
Cited by 8 | Viewed by 4695
Abstract
Cu(In,Ga)Se2 (CIGS)/CdS thin-film solar cells have reached, at laboratory scale, an efficiency higher than 22.3%, which is one of the highest efficiencies ever obtained for thin-film solar cells. The research focus has now shifted onto fabrication processes, which have to be easily [...] Read more.
Cu(In,Ga)Se2 (CIGS)/CdS thin-film solar cells have reached, at laboratory scale, an efficiency higher than 22.3%, which is one of the highest efficiencies ever obtained for thin-film solar cells. The research focus has now shifted onto fabrication processes, which have to be easily scalable at an industrial level. For this reason, a process is highlighted here which uses only the sputtering technique for both the absorber preparation and the deposition of all the other materials that make up the cell. Particular emphasis is placed on the comparison between different precursors obtained with either In2Se3 and Ga2Se3 or InSe and GaSe as starting materials. In both cases, the precursor does not require any heat treatment, and it is immediately ready to be selenized. The selenization is performed in a pure-selenium atmosphere and only lasts a few minutes at a temperature of about 803 K. Energy conversion efficiencies in the range of 15%–16% are reproducibly obtained on soda-lime glass (SLG) substrates. Similar results are achieved if commercial ceramic tiles are used as a substrate instead of glass. This result is especially useful for the so-called building integrated photovoltaic. Cu(In,Ga)Se2-based solar cells grown directly on ceramic tiles are ideal for the fabrication of ventilated façades in low impact buildings. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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7061 KiB  
Review
S-Rich CdS1−yTey Thin Films Produced by the Spray Pyrolysis Technique
by Shadia J. Ikhmayies
Energies 2016, 9(4), 234; https://doi.org/10.3390/en9040234 - 24 Mar 2016
Cited by 5 | Viewed by 4926
Abstract
Understanding the properties of CdSTe ternary alloys is important because they always form at the interface between the CdS window layer and CdTe absorber layer in CdS/CdTe solar cells due to the intermixing. This interdiffusion is necessary because it improves the device performance. [...] Read more.
Understanding the properties of CdSTe ternary alloys is important because they always form at the interface between the CdS window layer and CdTe absorber layer in CdS/CdTe solar cells due to the intermixing. This interdiffusion is necessary because it improves the device performance. Experimental work has been devoted to studying Te rich p-type CdSxTe1−x alloys, but there is a lack of studies on S-rich n-type CdS1−yTey solid solutions. In this work, a review of the structure, morphology, and optical properties of the S-rich n-type CdS1−yTey thin films produced by the spray pyrolysis technique on glass substrates is presented. Full article
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
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Submitted Abstracts

Title: S-Rich CdS1-yTey Thin Films Produced by the Spray Pyrolysis Technique
Author: Shadia J. Ikhmayies
Affiliations: Al Isra University, Faculty of Science, Department of Physics, Amman 11622, Jordan; E-mail: [email protected]
Abstract: Understanding the properties of the CdSTe ternary alloys is important because they always form at the interface between the CdS window layer and CdTe absorber layer in CdS/CdTe solar cells due to the intermixing. This interdiffusion is necessary because it improves the device performance. Experimental work was devoted to studying the Te rich p-type CdSxTe1-x alloy, but there is a lack in studying the S-rich n-type CdS1-yTey solid solution. In this work, a review of the structure, morphology, and optical properties of the S-rich n-type CdS1-yTey thin films produced by the spray pyrolysis technique on glass substrates is presented.
Keywords: CdS/CdTe solar cells, CdSxTe1-x solid solution, interdiffusion, spray pyrolysis, photoluminescence.

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