MRS Bulletin

Technical Feature

Technical Feature

Transparent Conducting Oxides for Photovoltaics

Elvira Fortunato, David Ginley, Hideo Hosono and David C. Paine

Abstract

Transparent conducting oxides (TCOs) are an increasingly important component of photovoltaic (PV) devices, where they act as electrode elements, structural templates, and diffusion barriers, and their work function controls the open-circuit device voltage. They are employed in applications that range from crystalline-Si heterojunction with intrinsic thin layer (HIT) cells to organic PV polymer solar cells. The desirable characteristics of TCO materials that are common to all PV technologies are similar to the requirements for TCOs for flat-panel display applications and include high optical transmissivity across a wide spectrum and low resistivity. Additionally, TCOs for terrestrial PV applications must use low-cost materials, and some may require device-technology-specific properties. We review the fundamentals of TCOs and the matrix of TCO properties and processing as they apply to current and future PV technologies.

Elvira Fortunato is an associate professor in the Materials Science Department at the New University of Lisbon and has been director of the Materials Research Centre (CENIMAT) since 1998.

She graduated in mate rials science from New University of Lisbon. Fortunato received her PhD degree from New University of Lisbon in 1995 and her Aggregation (teaching certificate) in 2005.

Fortunato pioneered European research on thin-film transistors based on oxide semiconductors, proving the capability to use oxide materials as true semiconductors. Her recent accomplishments include the first ZnO-based transparent thin-film transistor (TTFT) deposited at room temperature by rf magnetron sputtering with high field-effect mobility. Fortunato's current interests are in the design, fabrication, conduction transport mechanisms, and characterization of amorphous multicomponent oxide-based TTFTs.

Fortunato can be reached at Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Campus da FCT, 2829-516 Caparica, Portugal; tel. 351-21-2948562, fax 351-21-2948558, and e-mail elvira.fortunato@fct.unl.pt.

David Ginley is a group manager in proc ess technology and advanced concepts at the National Renewable Energy Laboratory, leading activities in the applications of nanotechnology, organic electronics, transition metal oxides (ferroelectric materials, rechargeable Li batteries, and transparent conductors), and inkjet printing. He is an adjunct professor of physics at the University of Colorado at Boulder and of materials science at the Colorado School of Mines.

Ginley graduated from the Colorado School of Mines with a BS degree in mineral engineering chemistry and received a PhD degree from MIT in inorganic chemistry. His work focuses on the development and basic science of high-quality materials (transparent conducting oxides, ferroelectric materials, organic materials, and nanomaterials) and the development of next-generation proc ess technology for materials and device development (combinatorial methods, direct-write materials, composite materials, and nonvacuum processing).

Ginley is a fellow of the Electrochemical Society and active in the Materials Research Society and IEEE. He has published more than 320 papers and holds 24 patents. He has been honored with a Department of Energy Award for Sustained Research in Superconducting Materials, and R&D 100 awards for novel chemical etches, nanopar ticle technology, ferroelectric frequency-agile electronics, and alumina-based nanofibers. He also has received two Federal Laboratory Consortium for Technology Transfer awards.

Ginley can be reached by e-mail at david_ginley@nrel.gov.

Hideo Hosono is a Professor in the Frontier Collaborative Research Center and the Materials and Structures Laboratory at Tokyo Institute of Technology in Japan.

He received both his BEng and DEng degrees in applied chemistry at Tokyo Metropolitan University. Afterward, Hosono was an associate professor at Nagoya Institute of Technology and the Institute of Molecular Science, and became a professor at Tokyo Tech in 1999.

That same year, he was named director of the ERATO Hosano Transparent Electro-Active Material project (1999–2004), sponsored by the Japan Science and Technology (JST) Agency. He currently is leading the JST project ERATO-SORST. He also leads the MEXT COE-21 program, “Nanoma te rial Cultivation for Industrial Collaboration,” for the Materials Group at Tokyo Tech.

Hosono has published close to 600 original papers and holds approximately 20 PCT patents. His current research explores novel electroactive transparent oxides and their device applications.

Hosono can be reached at Tokyo Institute of Technology, Mail Box R3-1, Materials and Structures Laboratory, Nagatsuta 4259, Midori, Yokohama 226-8503, Japan; tel. 81-45-924-5359, fax 81-45-924-5339, and e-mail hosono@msl.titech.ac.jp.

David C. Paine is a professor of engineering at Brown University. He earned his PhD degree in materials science from Stanford University in 1988. Paine's research includes thin-film characterization and processing with particular focus on transparent conducting oxides, sputter and ion-beam deposition, amorphous/crystalline phase transformations, microstructure evolution, interfaces and interface stability, physical vapor deposition, x-ray diffraction, electron micros copy, and, most recently, oxide-based electronics.

Paine can be reached Paine can be reached at Brown University, Division of Engineering, Box D, Providence, RI 02912 USA; e-mail david_paine@brown.edu.

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