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The role of ZnO in solar cell research

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The role of ZnO in solar cell research

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     The roles of ZnO in solar cells research

     Jia Jia

     Outline

     1. Introduction 2. ZnO in thin film solar cells 3. ZnO in dye sensitized solar cells

     1. Introduction

     Zinc oxide is a wide band gap compound semiconductor (Eg=3.2 eV)

     Fig. 1.2. (a) An orange zincite crystal from Sterling Mine, Ogdensburg, USA (collection: Rob Lavinsky,

    www.mineralienatlas.de/lexikon/index.php/Zinkit) and (b) a synthetic zinc oxide crystal (www.gc.maricopa.edu/earthsci/imagearchive/ zincite755.jpg). The mineral in (a) exhibits a size of 30 ?Á 25 ?Á 6mm3

     Fig. 1.3. Two views of the crystal structure of zinc oxide (ZnO). Left : Perspective view perpendicular to the c-axis. The upper side is the zinc terminated (0001) plane, the bottom plane is oxygen terminated (000?þ1). Right : View along the c-axis on the zinc terminated (0001) plane

     1. Introduction

     Advantages

     High transparency in visible and near infrared spectral region Possibility to prepare highly-doped films with free electron density and low resistivity. Good contacts to the active semiconductors Possibility to prepare the TCO layers on large scale Possibility to prepare ZnO films with suitable properties at low substrate temperature Possibility for preparation for tailored surfaces with suitable light scattering properties for light trapping Low material costs, non-toxicity and abundance

     2. ZnO in thin film solar cells

     Metal grid Anti-reflecting layer TCO Window layer Buffer layer Absorbing layer Back contact Substrate

     light

     p-type layer

     p-n junction

     + + + + + + + + + +

     n-type layer

     + + + + + + + +

     Current

     e-

     -

     Increase light light pass through, conducting Increase open circle

current Lattice match Absorbing layer Ohm contact

     Load

     2. ZnO in thin film solar cells

     Transparent conducting oxides(TCO) An important layer in thin film solar cells Transparent conducting oxides in general are n-type degenerate semiconductors with good electrical conductivity and high transparency in the visible spectrum. Thus, a low-resistance contact to the device and transmission of most of the incident light to the absorber layer is ensured.

     Transparent conductive zinc oxide: basics and applications in thin film (Book) By Klaus Ellmer, Andreas Klein, Bernd Rech

     2. ZnO in thin film solar cells

     High transparency Transparent materials possess bandgaps with energies corresponding to wavelengths which are shorter than the visible range (380 nm to 750 nm). The transparency of ZnO is due to their optical band gaps, which is ?Ý3.2 eV, leading to a transparency for wavelength >360 nm. High conductivity sheet resistance of pure ZnO : 100(

     /?õ ) ?õ

     Criteria for Choosing Transparent Conductors Roy G. Gordon MRS BULLETIN/AUGUST 2000

     2. ZnO in thin film solar cells

     n-type window layer in thin film solar cells

     Electrodeposition of semiconductors for optoelectronic devices: results on zinc oxide Thierry Pauporte?ä *, Daniel Lincot

     It is possible to take advantage of differing properties of two TCOs by forming a bilayer. High-efficiency CIGS and CdTe devices are generally fabricated with such bilayer structures, consisting of a highly conducting layer for low-resistance contact and lateral current collection and a much thinner highresistivity layer (called HR layer by CdTe groups and buffer layer by CIGS groups) of a suitable material, to minimize forward current through pinholes in the window layer.

     2. ZnO in thin film solar cells

     Progress toward 20% efficiency in Cu(In,Ga)Se2 polycrystalline thin-film solar cells Miguel A. Contreras1,*Brian Egaas1, K. Ramanathan1, J. Hiltner2, A. Swartzlander1, F. Hasoon1, Rommel Noufi1 Progress in Photovoltaics: Research and Applications Volume 7, Issue 4, pages 311?C316, July/August 1999

     2. ZnO in thin film solar cells

     Preparation of ZnO:Al/ZnO film

     Sputtering Chemical vapor deposition Pulsed-laser deposition Electrochemical deposition

     2. ZnO in thin film solar cells

     Preparation of ZnO:Al/ZnO film Sputtering

     The term ??sputtering?? means the ejection of atoms from a usually solid target material due to the impact of highly energetic species. The most common technique to deposit ZnO films is by sputtering technique.

     http://www.alyssahale.com/design.htm

     2. ZnO in thin film solar cells

     Preparation of ZnO film Direct Current Sputtering of ZnO film(DC)

     Transparent conductive zinc oxide: basics and applications in thin film (BOOK) By Klaus Ellmer, Andreas Klein, Bernd Rech

     2. ZnO in thin film solar cells

     Radio Frequency Sputtering of ZnO film (RF) RF sputtering is necessary when dielectric compounds are sputtered. Charge build-up on insulating targets can be avoided with the use of RF sputtering where the sign of the anode-cathode bias is varied at a high rate.

     Transparent ZnO thin-film transistor fabricated by rf magnetron sputtering P. F. Carcia,a) R. S. McLean, M. H. Reilly, and G. Nunes, Jr. APPLIED PHYSICS LETTERS VOLUME 82, NUMBER 7

     ZnO in thin film solar cells

     Preparation of ZnO film

     Texture etched ZnO:Al coated glass substrates for silicon based thin film solar cells O. Klutha,*, B. Recha, L. Houbena, S. Wiedera, G. Scho??pea, C. Benekinga, H. Wagnera, A. Lo??f?? b, H.W. Schockb

     2. ZnO in thin film solar cells

     Preparation of ZnO film

     Characterization and optimization of zinc oxide films by r.f. magnetron sputtering K.B. Sundaram, A. Khan

     Transparent conductive zinc oxide: basics and applications in thin film (book) By Klaus Ellmer, Andreas Klein, Bernd Rech

     2. ZnO in thin film solar cells

     Preparation of ZnO:Al film Radio Frequency Sputtering of ZnO:Al film (RF)

     Targets : A sintered oxide ceramic disk of ZnO (diameter 100 mm) mixed with 2 wt.% Al2O3 was used. Working pressure: pure Ar

     High transmittance and low resistive ZnO:Al films for thin film solar cells Jinsu Yooa, Jeonghul Leeb, Seokki Kimb, Kyunghoon Yoonb, I. Jun Parkb, S.K. Dhungela, B. Karunagarana, D. Mangalaraja, Junsin Yia

     2. ZnO in thin film solar cells

     ZnO:Al film

     The SEM micrographs of ZnO:Al films deposited on glass at 250 C, rf power 100 Wand Ar pressure of: (a) PAr =0:2 Pa; (b) PAr =1:0 Pa and (c) PAr =3:2 Pa.

     Optimisation of ZnO:Al films by change of sputter gas pressure for solar cell application Dengyuan Song*, Armin G. Aberle, James Xia

     2. ZnO in thin film solar cells

     Preparation of ZnO film Electrodeposition

     The basic principle is to use dissolved oxygen as the source for the synthesis of oxides, which is surprisingly not commonly used. The films are deposited cathodically from an aqueous/DMSO solution of zinc salt in the presence of dissolved oxygen according to the overall reaction given in Equation I.

     Experiments are carried out in solutions containing ZnCl2 salts at concentrations ranging between 10-3 and 10-1 M, with a supporting electrolyte of KCI (0.1 M). The oxygen concentration is fixed by bubbling oxygen/argon gas mixtures through the solution, leading to controlled oxygen concentrations in the range to a few 10-3M. The depositions are carried out for applied potentials in the range - 0.8 to - 1.4 V vsthe saturated mercurous sulfate Dr.Daniel Lincot electrode (MSE, Eo = + 0.65 V/NHE, the normal hydrogen electrode).[Cathodic Electrodeposition from Aqueous Solution of Dense or OpenStructured Zinc Oxide Films** By Sophie Peulon and Daniel Lincot]

     2. ZnO in thin film solar cells

     Preparation of ZnO film Electrodeposition

     Cathodic Electrodeposition from Aqueous Solution of Dense or Open-Structured Zinc Oxide Films** Electrochemical deposition of zinc oxide flms from nonBy Sophie Peulon and Daniel Lincot aqueous solution: a new buffer/window process for thin flm solar cells D. Gala, G. Hodesa,*, D. Lincotb, H.-W. Schockc

     2. ZnO in thin film solar cells

     Electrochemical deposition of zinc oxide films from non-aqueous solution: a new buffer/window process for thin film solar cells D. Gala, G. Hodesa,*, D. Lincotb, H.-W. Schockc Thin Solid Films 361?À362 (2000) 79-83

     2. ZnO in thin film solar cells

     Electrochemical deposition of zinc oxide films from non-aqueous solution: a new buffer/window process for thin film solar cells D. Gala, G. Hodesa,*, D. Lincotb, H.-W. Schockc Thin Solid Films 361?À362 (2000) 79-83

     3.ZnO in dye sensitized solar cells

     Dye-sensitised cells

     Dye-sensitised cells (DSCs) ?C are promising devices for inexpensive, large-scale solar energy conversion. The DSC is currently efficient and stable excitonic photocell. Central to this device is a thick nanoparticle film that provides a large surface area for the adsorption of light-harvesting molecules. However, nanoparticle DSCs rely on traplimited diffusion for electron transport, a slow mechanism that can limit device efficiency, especially at longer wavelengths.

     Review Dye-sensitized solar cells Michael Gr?tzel

     3.ZnO in dye sensitized solar cells

     ZnO in Dye-sensitised cells

     There is a new version of the dye-sensitised cell in which the traditional nanoparticle film is replaced by a dense array of oriented, crystalline ZnO nanowires. The direct electrical pathways provided by the nanowires ensure the rapid collection of carriers generated throughout the device, and a full Sun efficiency of 3.5% has been demonstrated.

     3.ZnO in dye sensitized solar cells

     Nanowire dye-sensitized solar cells MATT LAW1,2*, LORI E. GREENE1,2*, JUSTIN C. JOHNSON1, RICHARD SAYKALLY1 AND PEIDONG YANG1,2?

     3.ZnO in dye sensitized solar cells

     Preparation of ZnO nanowires in Dye-sensitised cells

     Arrays of ZnO nanowires were synthesized on FTO substrates that were first cleaned thoroughly by acetone/ethanol sonication and then coated with a thin film of ZnO quantum dots, 3?C4 nm in diameter, by dip-coating in a concentrated ethanol solution. Nanowires were grown by immersing seeded substrates in aqueous solutions containing 25 mM zinc nitrate hydrate, 25 mM hexamethylenetetramine and 5?C7 mM polyethylenimine at 92 ?ãC for 2.5 hours. Because nanowire growth slowed after this period, substrates were repeatedly introduced to fresh solution baths in order to obtain long wire arrays (total reaction times of up to 50 hours). The arrays were then rinsed with deionized water and baked in air at 400 ?ãC for 30 minutes to remove any residual organics and to optimize cell performance.

     Q&A

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