Special Issue "Novel Thin Film Materials for Photovoltaic Applications"

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A special issue of Coatings (ISSN 2079-6412).

Deadline for manuscript submissions: closed (31 August 2015)

Special Issue Editors

Guest Editor
Prof. Dr. Francesco Di Benedetto

Dipartimento di Chimica, Università di Firenze, Italy
Website | E-Mail
Guest Editor
Prof. Dr. Susan Schorr

Crystallography, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, Berlin, Germany
Website | E-Mail
Phone: +49 030 8062 42317

Special Issue Information

Dear Colleagues,

The energy predicament, due to the impending Hubbert’s Peak Oil theory combined with the environmental consequences of CO2 emissions, dictate the need for a rapid transition from fossil fuels to renewable and sustainable energy sources to power the social and economic global metabolism. The last few years have witnessed an exponential growth of renewable power produced in major developed countries, mostly from wind farms and photovoltaic (PV) plants.
The growing demand of energy represents the main driving force of research in the field of new PV materials and new technological solutions, in order to confront two apparent problems: the rarefaction of the mineral resources and the need of developing an environmentally friendly and sustainable energy supply system.
The aim of this Special Issue consists of attracting worldwide researchers in participating to create a state-of-the-art summary of the recent increase in scientific and technological knowledge on new materials for thin film technology. This could include specific references to the synthetic routes for absorber powders and crystals, to the strategies for the realization of thin film devices, the characterization of the mineralogical, crystal chemical, structural, thermodynamic and physical properties of substrates and devices, and perspectives for the subject.
In this respect, special emphasis will be given to new data on consolidated materials for thin film technology, such as for example, cadmium telluride (CdTe), copper indium gallium sulfides and selenides, Cu(In,Ga)S2/Se2 (CIGS, CIGSe), new promising materials such as kesterites,Cu2ZnSnS4 or Cu2ZnSnSe4 (CZTS, CZTSe), as well as other emerging materials for thin film solar cell applications.

Prof. Dr. Francesco Di Benedetto
Prof. Dr. Susan Schorr
Guest Editors

Submission

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. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as 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.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 300 CHF (Swiss Francs). English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

Keywords

  • photovoltaic materials
  • thin film technology
  • CdTe
  • chalcopyrites
  • CIGS
  • kesterites
  • CZTS
  • new materials
  • materials and thin film characterization

Published Papers (11 papers)

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Research

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Open AccessArticle Fabrication and Characterization of a Perovskite-Type Solar Cell with a Substrate Size of 70 mm
Coatings 2015, 5(4), 646-655; doi:10.3390/coatings5040646
Received: 25 June 2015 / Revised: 15 September 2015 / Accepted: 6 October 2015 / Published: 13 October 2015
Cited by 2 | PDF Full-text (768 KB) | HTML Full-text | XML Full-text
Abstract
A perovskite-type solar cell with a substrate size of 70 mm × 70 mm was fabricated by a simple spin-coating method using a mixed solution. The photovoltaic properties of the TiO2/CH3NH3PbI3-based photovoltaic devices were investigated
[...] Read more.
A perovskite-type solar cell with a substrate size of 70 mm × 70 mm was fabricated by a simple spin-coating method using a mixed solution. The photovoltaic properties of the TiO2/CH3NH3PbI3-based photovoltaic devices were investigated by current density-voltage characteristic and incident photon to current conversion efficiency measurements. Their short-circuit current densities were almost constant over a large area. The photoconversion efficiency was influenced by the open-circuit voltage, which depended on the distance from the center of the cell. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessArticle Electrical and Optical Properties of Fluorine Doped Tin Oxide Thin Films Prepared by Magnetron Sputtering
Coatings 2014, 4(4), 732-746; doi:10.3390/coatings4040732
Received: 24 September 2014 / Revised: 15 October 2014 / Accepted: 24 October 2014 / Published: 30 October 2014
Cited by 9 | PDF Full-text (990 KB) | HTML Full-text | XML Full-text
Abstract
Fluorine doped tin oxide (FTO) coatings have been prepared using the mid-frequency pulsed DC closed field unbalanced magnetron sputtering technique in an Ar/O2 atmosphere using blends of tin oxide and tin fluoride powder formed into targets. FTO coatings were deposited with a
[...] Read more.
Fluorine doped tin oxide (FTO) coatings have been prepared using the mid-frequency pulsed DC closed field unbalanced magnetron sputtering technique in an Ar/O2 atmosphere using blends of tin oxide and tin fluoride powder formed into targets. FTO coatings were deposited with a thickness of 400 nm on glass substrates. No post-deposition annealing treatments were carried out. The effects of the chemical composition on the structural (phase, grain size), optical (transmission, optical band-gap) and electrical (resistivity, charge carrier, mobility) properties of the thin films were investigated. Depositing FTO by magnetron sputtering is an environmentally friendly technique and the use of loosely packed blended powder targets gives an efficient means of screening candidate compositions, which also provides a low cost operation. The best film characteristics were achieved using a mass ratio of 12% SnF2 to 88% SnO2 in the target. The thin film produced was polycrystalline with a tetragonal crystal structure. The optimized conditions resulted in a thin film with average visible transmittance of 83% and optical band-gap of 3.80 eV, resistivity of 6.71 × 10−3 Ω·cm, a carrier concentration (Nd) of 1.46 × 1020 cm−3 and a mobility of 15 cm2/Vs. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessArticle Fabrication of CdS/CdTe-Based Thin Film Solar Cells Using an Electrochemical Technique
Coatings 2014, 4(3), 380-415; doi:10.3390/coatings4030380
Received: 9 April 2014 / Revised: 11 June 2014 / Accepted: 11 June 2014 / Published: 27 June 2014
Cited by 19 | PDF Full-text (3397 KB) | HTML Full-text | XML Full-text
Abstract
Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results
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Thin film solar cells based on cadmium telluride (CdTe) are complex devices which have great potential for achieving high conversion efficiencies. Lack of understanding in materials issues and device physics slows down the rapid progress of these devices. This paper combines relevant results from the literature with new results from a research programme based on electro-plated CdS and CdTe. A wide range of analytical techniques was used to investigate the materials and device structures. It has been experimentally found that n-, i- and p-type CdTe can be grown easily by electroplating. These material layers consist of nano- and micro-rod type or columnar type grains, growing normal to the substrate. Stoichiometric materials exhibit the highest crystallinity and resistivity, and layers grown closer to these conditions show n → p or p → n conversion upon heat treatment. The general trend of CdCl2 treatment is to gradually change the CdTe material’s n-type electrical property towards i-type or p-type conduction. This work also identifies a rapid structural transition of CdTe layer at 385 ± 5 °C and a slow structural transition at higher temperatures when annealed or grown at high temperature. The second transition occurs after 430 °C and requires more work to understand this gradual transition. This work also identifies the existence of two different solar cell configurations for CdS/CdTe which creates a complex situation. Finally, the paper presents the way forward with next generation CdTe-based solar cells utilising low-cost materials in their columnar nature in graded bandgap structures. These devices could absorb UV, visible and IR radiation from the solar spectrum and combine impact ionisation and impurity photovoltaic (PV) effect as well as making use of IR photons from the surroundings when fully optimised. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessArticle Microstructures and Photovoltaic Properties of Zn(Al)O/Cu2O-Based Solar Cells Prepared by Spin-Coating and Electrodeposition
Coatings 2014, 4(2), 203-213; doi:10.3390/coatings4020203
Received: 20 January 2014 / Revised: 17 March 2014 / Accepted: 20 March 2014 / Published: 31 March 2014
Cited by 7 | PDF Full-text (760 KB) | HTML Full-text | XML Full-text
Abstract
Copper oxide (Cu2O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu2O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on
[...] Read more.
Copper oxide (Cu2O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu2O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on In-doped tin oxide/ZnO/Cu2O/Au heterojunction structures. Short-circuit current and fill factor increased by aluminum (Al) doping in the ZnO layer, which resulted in the increase of the conversion efficiency. The efficiency was improved further by growing ZnO and Cu2O layers with larger crystallite sizes, and by optimizing the Al-doping by spin coating. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessArticle Spray-on PEDOT:PSS and P3HT:PCBM Thin Films for Polymer Solar Cells
Coatings 2014, 4(1), 85-97; doi:10.3390/coatings4010085
Received: 6 December 2013 / Revised: 31 December 2013 / Accepted: 8 January 2014 / Published: 21 January 2014
Cited by 6 | PDF Full-text (820 KB) | HTML Full-text | XML Full-text
Abstract
PEDOT:PSS electron-blocking layer, and PEDOT:PSS + P3HT:PCBM stacked layers are fabricated by ultrasonic atomization and characterized by scanning electron microscopy (SEM) and optical profilometry. The measured thicknesses based on SEM and optical profilometry are quite different, indicating the incapability of measurement techniques for
[...] Read more.
PEDOT:PSS electron-blocking layer, and PEDOT:PSS + P3HT:PCBM stacked layers are fabricated by ultrasonic atomization and characterized by scanning electron microscopy (SEM) and optical profilometry. The measured thicknesses based on SEM and optical profilometry are quite different, indicating the incapability of measurement techniques for non-uniform thin films. The thickness measurements are compared against theoretical estimations and a qualitative agreement is observed. Results indicate that using a multiple pass fabrication strategy results in a more uniform thin film. It was also found that the film characteristics are a strong function of solution concentration and spraying passes, and a weak function of substrate speed. Film thickness increases with solution concentration but despite the prediction of theory, the increase is not linear, indicating a change in the film porosity and density, which can affect physical and opto-electrical properties. Overall, while spray coating is a viable fabrication process for a wide range of solar cells, film characteristics can be easily altered by a change in process parameters. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessArticle An Investigation into W or Nb or ZnFe2O4 Doped Titania Nanocomposites Deposited from Blended Powder Targets for UV/Visible Photocatalysis
Coatings 2013, 3(3), 153-165; doi:10.3390/coatings3030153
Received: 27 June 2013 / Revised: 5 August 2013 / Accepted: 6 August 2013 / Published: 14 August 2013
PDF Full-text (1692 KB) | HTML Full-text | XML Full-text
Abstract
The photocatalytic behavior of titania coatings is largely determined by their crystalline structure. Depending on deposition conditions, though, titania may form amorphous, brookite, anatase or rutile structures, with anatase or anatase/rutile mixed phase structures showing the highest levels of activity. Anatase is activated
[...] Read more.
The photocatalytic behavior of titania coatings is largely determined by their crystalline structure. Depending on deposition conditions, though, titania may form amorphous, brookite, anatase or rutile structures, with anatase or anatase/rutile mixed phase structures showing the highest levels of activity. Anatase is activated by UV light and, consequently, there is a great deal of interest in doping titania films to both increase activity and extend it into the visible range. In this study, titania and doped titania coatings have been deposited from blended oxide powder targets. This highly versatile and economical technique allows dopant levels to be readily varied. Using this technique, titania coatings doped with W, Nb and ZnFe2O4 have been deposited onto glass substrates by pulsed magnetron sputtering. The as-deposited coatings were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analyzed. Structural transformation of the titania coatings was initiated in the 500–600 °C range, with the coatings annealed at 700 °C having predominantly anatase structures. The photocatalytic activity of the coatings was assessed through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It was found that, after annealing, coatings with photo-active surfaces were produced and that activity varied with dopant content. Activity levels under fluorescent light irradiation were up to 60% of the activity measured under UV irradiation. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)

Review

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Open AccessReview Review on the Photocatalyst Coatings of TiO2: Fabrication by Mechanical Coating Technique and Its Application
Coatings 2015, 5(3), 425-464; doi:10.3390/coatings5030425
Received: 18 June 2015 / Revised: 16 July 2015 / Accepted: 22 July 2015 / Published: 30 July 2015
Cited by 2 | PDF Full-text (17447 KB) | HTML Full-text | XML Full-text
Abstract
This review presents the latest results of studies directed at photocatalyst coatings of titanium dioxide (TiO2) prepared by mechanical coating technique (MCT) and its application. Compared with traditional coating techniques, MCT is a simple, low cost and useful coating formation process,
[...] Read more.
This review presents the latest results of studies directed at photocatalyst coatings of titanium dioxide (TiO2) prepared by mechanical coating technique (MCT) and its application. Compared with traditional coating techniques, MCT is a simple, low cost and useful coating formation process, which is proposed and developed based on mechanical frictional wear and impacts between substrate materials and metal powder particles in the bowl of planetary ball mill. The formation process of the metal coatings in MCT includes four stages: The nucleation by adhesion, the formation and coalescence of discrete islands, formation and thickening of continuous coatings, exfoliation of continuous coatings. Further, two-step MCT was developed based on the MCT concept for preparing composite coatings on alumina (Al2O3) balls. This review also discusses the influence on the fabrication of photocatalyst coatings after MCT and improvement of its photocatalytic activity: oxidation conditions, coating materials, melt salt treatment. In this review, the oxidation conditions had been studied on the oxidation temperature of 573 K, 673 K, 773 K, 873 K, 973 K, 1173 K and 1273 K, the oxidation time of 0.5 h, 1 h, 3 h, 10 h, 15 h, 20 h, 30 h, 40 h, and 50 h. The photocatalyst coatings showed the highest photocatalytic activity with the oxidation condition of 1073 K for 15 h. The metal powder of Ti, Ni and Cr had been used as the coating materials. The composite metal powder could affect the surface structure and photocatalytic activity. On the other hand, the melt salt treatment with KNO3 is an effective method to form the nano-size structure and enhance photocatalytic activity, especially under visible light. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessReview Chalcopyrite Thin Film Materials for Photoelectrochemical Hydrogen Evolution from Water under Sunlight
Coatings 2015, 5(3), 293-311; doi:10.3390/coatings5030293
Received: 30 May 2015 / Revised: 4 July 2015 / Accepted: 14 July 2015 / Published: 17 July 2015
Cited by 6 | PDF Full-text (940 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Copper chalcopyrite is a promising candidate for a photocathode material for photoelectrochemical (PEC) water splitting because of its high half-cell solar-to-hydrogen conversion efficiency (HC-STH), relatively simple and low-cost preparation process, and chemical stability. This paper reviews recent advances in copper chalcopyrite photocathodes. The
[...] Read more.
Copper chalcopyrite is a promising candidate for a photocathode material for photoelectrochemical (PEC) water splitting because of its high half-cell solar-to-hydrogen conversion efficiency (HC-STH), relatively simple and low-cost preparation process, and chemical stability. This paper reviews recent advances in copper chalcopyrite photocathodes. The PEC properties of copper chalcopyrite photocathodes have improved fairly rapidly: HC-STH values of 0.25% and 8.5% in 2012 and 2015, respectively. On the other hand, the onset potential remains insufficient, owing to the shallow valence band maximum mainly consisting of Cu 3d orbitals. In order to improve the onset potential, we explored substituting Cu for Ag and investigate the PEC properties of silver gallium selenide (AGSe) thin film photocathodes for varying compositions, film growth atmospheres, and surfaces. The modified AGSe photocathodes showed a higher onset potential than copper chalcopyrite photocathodes. It was demonstrated that element substitution of copper chalcopyrite can help to achieve more efficient PEC water splitting. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessReview Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding
Coatings 2014, 4(2), 282-307; doi:10.3390/coatings4020282
Received: 18 February 2014 / Revised: 17 April 2014 / Accepted: 24 April 2014 / Published: 30 April 2014
Cited by 22 | PDF Full-text (1142 KB) | HTML Full-text | XML Full-text
Abstract
Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet
[...] Read more.
Cadmium chloride treatment is a key processing step identified in the late 1970s to drastically improve the solar to electric conversion efficiency of CdS/CdTe thin film solar cells. Although a large body of experimental results are available to date, this process is yet to be understood even after three decades of research. This paper reviews the experimental results available, presents some new clues leading to improved understanding and suggests key research areas necessary to fully understand this crucial processing step. Improved understanding will lead to further increase in conversion efficiency of CdS/CdTe solar cells well beyond 20%. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessReview Applications of Oxide Coatings in Photovoltaic Devices
Coatings 2014, 4(1), 162-202; doi:10.3390/coatings4010162
Received: 10 February 2014 / Accepted: 10 March 2014 / Published: 24 March 2014
Cited by 8 | PDF Full-text (919 KB) | HTML Full-text | XML Full-text
Abstract
Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer
[...] Read more.
Metalloid and metal based oxides are an almost unavoidable component in the majority of solar cell technologies used at the time of writing this review. Numerous studies have shown increases of ≥1% absolute in solar cell efficiency by simply substituting a given layer in the material stack with an oxide. Depending on the stoichiometry and whether other elements are present, oxides can be used for the purpose of light management, passivation of electrical defects, photo-carrier generation, charge separation, and charge transport in a solar cell. In this review, the most commonly used oxides whose benefits for solar cells have been proven both in a laboratory and industrial environment are discussed. Additionally, developing trends in the use of oxides, as well as newer oxide materials, and deposition technologies for solar cells are reported. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)
Open AccessReview Spray-on Thin Film PV Solar Cells: Advances, Potentials and Challenges
Coatings 2014, 4(1), 60-84; doi:10.3390/coatings4010060
Received: 6 December 2013 / Revised: 3 January 2014 / Accepted: 8 January 2014 / Published: 21 January 2014
Cited by 21 | PDF Full-text (656 KB) | HTML Full-text | XML Full-text
Abstract
The capability to fabricate photovoltaic (PV) solar cells on a large scale and at a competitive price is a milestone waiting to be achieved. Currently, such a fabrication method is lacking because the effective methods are either difficult to scale up or expensive
[...] Read more.
The capability to fabricate photovoltaic (PV) solar cells on a large scale and at a competitive price is a milestone waiting to be achieved. Currently, such a fabrication method is lacking because the effective methods are either difficult to scale up or expensive due to the necessity for fabrication in a vacuum environment. Nevertheless, for a class of thin film solar cells, in which the solar cell materials can be processed in a solution, up scalable and vacuum-free fabrication techniques can be envisioned. In this context, all or some layers of polymer, dye-sensitized, quantum dot, and copper indium gallium selenide thin film solar cells illustrate some examples that may be processed in solution. The solution-processed materials may be transferred to the substrate by atomizing the solution and carrying the spray droplets to the substrate, a process that will form a thin film after evaporation of the solvent. Spray coating is performed at atmospheric pressure using low cost equipment with a roll-to-roll process capability, making it an attractive fabrication technique, provided that fairly uniform layers with high charge carrier separation and transport capability can be made. In this paper, the feasibility, the recent advances and challenges of fabricating spray-on thin film solar cells, the dynamics of spray and droplet impaction on the substrate, the photo-induced electron transfer in spray-on solar cells, the challenges on characterization and simulation, and the commercialization status of spray-on solar cells are discussed. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Photovoltaic Applications)

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