For dye-sensitized solar cell (DSSC), an efficient transport of electron from the dye sensitizer through the mesoporous
oxide layer and to be collected by electrode is crucial for high photovoltaic conversion efficiency. In this work, two
novel approaches were developed in DSSC fabrication to improve the overall photovoltaic performance. The concurrent
improvement in the charge transport property and light harvesting efficiency was achieved by incorporating N-doped
TiO<sub>2</sub> in the mesoporous TiO2 layer of the photoanode. These N-doped TiO<sub>2</sub> (TiN<sub>x</sub>O<sub>y</sub>) was formed by using the single step thermal oxidation of Titanium Nitride (TiN) nanomaterials. At the same time, the 3D electrode with SnO<sub>2</sub> nanorods grown on the FTO glass using plasma enhanced chemical vapor deposition (PECVD) system was used to enhance the charge collection efficiency. By combining these two approaches simultaneously, the DSSC with composite TiN<sub>x</sub>O<sub>y</sub>-TiO<sub>2</sub> photoanode on SnO<sub>2</sub> nanorods 3D electrode was successfully fabricated and characterized. As compared to the standard DSSC, an overall increment of 28 % in the conversion efficiency was achieved. Higher incident photon-current conversion efficiency (IPCE) values were also obtained, specifically for the region 400 – 500 nm due to the cosensitization effect of N-doped TiO<sub>2. </sub>Efficient transfer of electron due to the decrease in charge transfer resistance at the mesoporous oxide/dye/electrolyte interface was observed from electrochemical impedance spectroscopy (EIS) measurement. With the use of SnO<sub>2</sub> nanorods, the adhesion between the mesoporous TiO<sub>2/</sub>FTO was enhanced and the transit time of a photogenerated electron through the mesoporous layer before being collected at the FTO electrode was significantly reduced by 50 %.
Micromachining processes have been extensively adapted in developing uncooled infrared imaging array. One of the most important sensing materials in the array is ferroelectric thin film. To integrate the ferroelectric thin film with the signal processing circuitry, an IC compatible process has to be applied. Various methods have been successfully used to prepare high quality oxide ferroelectric thin films. Unfortunately, not all of the methods are compatible with a standard CMOS process. None of them can optimize the ferroelectric thin film after it has been deposited onto IC chip due to high heat treatment temperature. A Flip-Chip Transfer (FCT) method is proposed here to optimize the ferroelectric thin film separately with the IC chip. Doing so, any necessary measure could be taken to optimize the performance of the ferroelectric thin film. After that, anisotropic conductive film (ACF) is applied between the ferroelectric thin film and the IC chip to establish interconnection and mechanical bonding between the sensing element and the signal processing circuit. Micromachining process is then applied to remove the substrate, usually Si, on which the sensing material is deposited. A 128x1 linear pyroelectric infrared imaging array is being fabricated.
Design and fabrication of a 32 X 32 uncooled IR focal plane array based on Si micromachining technique is presented. Ferroelectric lead zirconate titanate (PZT) thin film was used as the sensing material in the array. The PZT thin film was deposited on the top of Si substrate coated with silicon dioxide, silicon nitrite, titanium and platinum. Sol-gel method was used to deposit the PZT film. Size of the sensing element is 60 X 80 micrometers <SUP>2</SUP> and pixel size is 80 X 100 micrometers <SUP>2</SUP>, yields a filling factor of 60%. In order to eliminate the thermal loss from the PZT elements to silicon substrate to improve the response of the IR sensor, silicon substrate under the sensing element was etched off using KOH micromachining technique. Membrane composed of silicon dioxide and silicon nitride was formed. Membrane size as large as 3.2 X 3.8 mm<SUP>2</SUP> is fabricated. Results proved that micromachining is an effective way in fabricating uncooled IR focal plane array based on ferroelectric thin films. The process is totally compatible with standard IC fabrication techniques.
Conference Committee Involvement (5)
Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems IV
10 December 2008 | Melbourne, Australia
Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems III
11 December 2006 | Adelaide, Australia
Device and Process Technologies for Microelectronics, MEMS, and Photonics IV
12 December 2005 | Brisbane, Australia
Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II
13 December 2004 | Sydney, Australia
Device and Process Technologies for Microelectronics, MEMS, and Photonics