Mr. Kai-Yin Cheung Profile

Kai-Yin Cheung

at Univ of Hong Kong

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Proceedings Article | 4 September 2009 Paper

Effect of fabrication processes on bulk heterojunctions (BHJ) photovoltaic device performance

K. Cheung, C. Yip, M. Fung, A. Djurisic, W. Chan, Z. He, X. Wang, C. Ho, W. Wong

Proc. SPIE. 7416, Organic Photovoltaics X

KEYWORDS: Photovoltaics, Magnesium, Roads, Organic photovoltaics, Electrodes, Polymers, Solar cells, Platinum, Aluminum, Heterojunctions

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Organic photovoltaic (OPV) devices have attracted much interest in recent decades because they have a great potential for low cost solar cells. Among different kinds of organic solar cells, conjugated polymer/fullerene bulk heterojunction (BHJ) solar cells have exhibited improvements in the power conversion efficiency (PCE) in recent years. The performance of BHJ solar cells is highly dependent on different fabrication processes. To address this issue, we focus on the dependence of different photovoltaic parameters on the fabrication methods. BHJ solar cells fabricated using platinum metallopolyyne (P1) with a low band gap of 1.85 eV as an electron donor and phenyl-C61-butyric acid methyl ester (PCBM) as an electron acceptor have been studied. The fabrication parameters, such as ratios of P1 to PCBM, solvents used, thickness of the active layers and top contact materials, have been systematically investigated. Blend ratio and solvent used had most significant influence on photovoltaic performance with several times higher efficiency of the best condition compared to the worst condition. They affected all photovoltaic parameters [open circuit voltage (V_oc), short circuit current density (J_sc) and the fill factor (FF)]. Top contact materials affected the V_oc and the FF, while thickness of the active layer mainly affected the J_sc and FF. The influence of different fabrication conditions on photovoltaic performance has been discussed.

Proceedings Article | 17 October 2007 Paper

Titania nanotube array based photovoltaic cells

C. T. Yip, K. Y. Cheung, A. B. Djurišić, W. K. Chan

Proc. SPIE. 6656, Organic Photovoltaics VIII

KEYWORDS: Titanium, Annealing, Solar cells, Crystals, Nitrogen, Scanning electron microscopy, Transmission electron microscopy, Dye sensitized solar cells, Electron transport, Temperature metrology

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It has been shown that dye sensitized solar cells (DSSCs) based on porous titanium dioxide (titania) layers have efficiencies exceeding 10%. Although porous structure has the advantage of large surface area for light harvesting, electron transport through the random nanoparticle network forming a porous film results in electron mobilities which are two orders of magnitude lower compared to the single crystal materials. Therefore, considerable efforts have been made to fabricate DSSC based on one dimensional nanostructures, such as nanowires or nanotubes. Titania nanotube arrays are typically made by anodization of titanium, followed by annealing to improve crystallinity. In this work, we investigated the influence of annealing temperature and annealing atmosphere on the crystal structure, the electron transport, and the solar cell performance of titania nanotube arrays. The titania nanotube arrays were prepared from electrochemically anodized titanium foils and their morphology and crystal structure were characterized by scanning electron microscopy and transmission electron microscopy. The crystal phases and the compositions of nanotube arrays were further investigated by X-ray diffraction for different annealing temperatures and X-ray photoelectron spectroscopy for different annealing atmospheres. For optimal annealing conditions, the short circuit current density of 4.27 mA/cm² and power conversion efficiency of 1.30% could be achieved under AM 1.5 simulated solar irradiation for 2 μm long nanotubes.

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