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2114 KiB

Open AccessArticle

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 - 4 Jan 2017

Cited by 5 | Viewed by 3772

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

Open AccessArticle

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 5888

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

Open AccessArticle

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 16 | Viewed by 5574

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

Open AccessArticle

Advances in Thin-Film Si Solar Cells by Means of SiO_x 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 13 | Viewed by 5344

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-SiO_x: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

Open AccessFeature PaperEditor’s ChoiceArticle

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 23 | Viewed by 7783

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

Open AccessArticle

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 4960

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 (X_c) 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

Open AccessArticle

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 34 | Viewed by 7300

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 10⁴Ω·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

Open AccessReview

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 5062

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

Open AccessReview

S-Rich CdS_1−yTe_y 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 5251

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 CdS_xTe_1−x alloys, but there is a lack of studies on S-rich n-type CdS_1−yTe_y solid solutions. In this work, a review of the structure, morphology, and optical properties of the S-rich n-type CdS_1−yTe_y 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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