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Energies 2016, 9(6), 402; doi:10.3390/en9060402

Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells

1
Department of Electrical Engineering, National Chung Hsing University, Taichung 40227, Taiwan
2
Graduate Institute of Optoelectronic Engineering, National Chung Hsing University, Taichung 40227, Taiwan
3
Research Center for Sustainable Energy and Nanotechnology, National Chung Hsing University, Taichung 40227, Taiwan
4
Green Energy and Environment Research Laboratories, Industrial Technology Research Institute, Chutung 310, Taiwan
*
Author to whom correspondence should be addressed.
Academic Editor: Alessio Bosio
Received: 8 March 2016 / Revised: 16 May 2016 / Accepted: 19 May 2016 / Published: 25 May 2016
(This article belongs to the Special Issue Key Developments in Thin Film Solar Cells)
View Full-Text   |   Download PDF [1701 KB, uploaded 25 May 2016]   |  

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 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. View Full-Text
Keywords: titanium oxide; chemically grown; heterojunction; band alignment; hole tunneling titanium oxide; chemically grown; heterojunction; band alignment; hole tunneling
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Lee, Y.-T.; Lin, F.-R.; Lin, T.-C.; Chen, C.-H.; Pei, Z. Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells. Energies 2016, 9, 402.

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