Recent Advances of Dye-Sensitized Solar Cells and Integrated Modules at SHARP
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1211-R12-02
RECENT ADVANCES OF DYE-SENSITIZED SOLAR CELLS AND INTEGRATED MODULES AT SHARP Naoki Koide, Ryohsuke Yamanaka, Hiroyuki Katayama New Technology Development Center, Solar Systems Development Group, SHARP CORPORATION, 282-1 Hajikami, Katsuragi, Nara 639-2198, Japan ABSTRACT An equivalent circuit for DSCs was studied using electrochemical impedance spectroscopy measurement, and the improvements of conversion efficiency of DSCs for not only single cells but also integrated modules were investigated. Further improvement of cell characteristics of DSCs was also investigated from the view point of modified TiO2 films and series-internal resistance design. The series-internal resistance elements were found to correlate positively with the sheet resistance of the transparent conducting oxide and the thickness of the electrolyte layer and negatively with the roughness factor of the platinum counter-electrode. The short circuit current density (Jsc) of the DSCs was effectively improved by use of a high-haze TiO2 film. In addition, the analysis of TiO2/dye interface by scanning probe microscopy and transient absorption spectroscopy were also useful for the study. As a result, the maximum single cell conversion efficiency of over 11% was obtained. Furthermore, an integrated DSC module composed of many rectangular cells connected in series was fabricated and the efficiency was increased to 8.4% (confirmed by AIST) by realizing high active area and high uniformity. INTRODUCTION During the past decade, much attention has been paid to the development of dyesensitized solar cells (DSCs) because of their simple structure and their potential for low-cost manufacturing. [1,2] DSCs have been widely studied since Grätzel and co-workers first announced their prospective development. A DSC, generally, comprises a nanocrystalline titanium dioxide (TiO2) electrode modified with a dye formed on a transparent conducting oxide (TCO), a platinum (Pt) counter electrode, and an electrolyte solution with a dissolved iodide ion/tri-iodide ion redox couple between the electrodes. In our earlier work, we had investigated the internal resistance of DSCs through electrochemical impedance spectroscopy and proposed an equivalent circuit of DSCs, and achieved the energy conversion efficiency of over 10% (confirmed in AIST) by improving short circuit current density (Jsc) and fill factor (FF) based on the analysis of the equivalent circuit. [3,4] However, the efficiency of DSCs was not high enough compared with bulk silicon solar cells. On the other hand, the upscaling of DSCs to large area panels was also progressed rapidly during last decades. There are two types of the module designs proposed: a parallel grids module design and an integrated module design. Many studies focus to parallel grids module design since a high active area is easily obtained. This type module is composed of a large-size single cell having current-collecting silver grids to reduce the sheet resistance of TCO. Although active area efficiency from 3% to 6% had been report
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