報告書番号

Q04003

タイトル（和文）

色素増感太陽電池の光電変換特性の分析(II) -ダイオードモデルの理想因子による電流-電圧特性の解析-

タイトル（英文）

Analysis of energy conversion characteristics in dye-sensitized nanocrystalline solar cells(II) -Ideality Factor of the Diode Model for Current-Voltage Characteristics-

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究報告では、ダイオードモデルの理想因子nを調べることを目的に、市販の酸化チタン粉末P25を用いて製作した色素増感太陽電池の電流-電圧特性を解析した。セルの製作方法を改善することによって、P25から作った従来の色素増感太陽電池と比較して高効率なセルが製作できた。この高効率セルで、ダイオードモデルでnの値を適切に選ぶことによって、実験の電流-電圧特性とよく合う理論的な電流-電圧特性を得た。これを基に、入射光強度、微結晶電極膜厚および光波長を種々変化させてnを調べた。その結果、光強度はnに影響しなかったのに対して、微結晶電極膜厚と光波長の変化によってnは顕著に変化した。さらに、微結晶電極の光透過特性と暗電流を調べ、酸化チタン/電解液界面の再結合が局在化して起こるTCO近傍での電子蓄積が理想因子に大きな影響を持っていると示唆される結果を得た。

概要 （英文）

Current-voltage characteristics (I-Vs) of dye-sensitized solar cells (DSCs) were analyzed with an empirical model of the diode equation. In high efficiency cells prepared from a commercial TiO2 powder, the perfect fit of experimental I-Vs to theoretical ones was attained with the diode model. On the basis of the successful simulations of the I-Vs, the ideality factor was studied as a function of light intensity, nanocrystalline film thickness, and light wavelength. Clear variations of an ideality factor from 2.9 to 4.5 depending on the film thickness and the light wavelength were revealed, in contrast to independence on the light intensity. These indicate that analysis of the ideality factor is a key of elucidation of the energy conversion mechanisms of DSCs, and, hence, leads to development of a first principle simulation model. Light transmittance and dark I-V measurements were also carried out. The light transmittance measurements of nanocrystalline films have revealed that the dependence of the ideality factor on the light wavelength is explained by photoelectron distribution, which depends on light absorption and scattering in the nanocrystalline electrode; that is, accumulation of the electrons near the transparent conductive oxide (TCO) substrate rather than a homogeneous distribution increases ideality factors. This explanation is consistent with the ideality factor variations due to the film thickness as well. The dark I-V measurements have indicated that leakage current from the TCO substrate to the electrolyte is not responsible for the I-Vs, and, furthermore, the dark current is localized at a narrow part near the TCO substrate in the nanocrystalline TiO2 electrode. Under the dark, the lowest ideality factor of 2.7 was observed; since the electron accumulation is a minimum in the dark, similarity of the dark ideality factor to 2.9 under the least photoelectron accumulation is consistent with the above explanation. In conclusion, the ideality factor has a deep relationship with the electron accumulation at a near-TCO region, where the localized TiO2/electrolyte-interfacial recombination is expected.

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