報告書番号

T99056

タイトル（和文）

色素増感太陽電池の酸化チタン微結晶電極での光散乱を応用した効率向上方策の検討 -光散乱の定式化による理論的解析-

タイトル（英文）

Theoretical Study of Improvement of Energy Conversion Efficiency by Application of Light Scattering to Dye-Sensitized Nanocrystalline Photoelectrochemical Solar Cells

概要 （図表や脚注は「報告書全文」に掲載しております）

色素増感大陽電池の酸化チタン粒子による光散乱の総合的な理論的解析結果を報告する。最初に、マクスウエル方程式の解に基づいた多孔質膜内での光散乱のモンテカルロシミュレーションの定式化を行った。酸化チタン微粒子からなる多孔質膜での光散乱を計算した結果、増感色素が無い場合、比較的良質な膜ならばほぼ透明な多孔質膜が製作できることを明らかにした。次に、前記のような透明な多孔質膜を色素で増感した電極内にサブミクロンサイズの酸化チタン粒子を添加した膜での光散乱を解析した。その結果、比較的小さい粒子は凝集させることにより散乱能を改善できることが分かった。また、光路長の増加の効果と光閉じ込め効果の２つの効果の内、光閉じ込め効果がより重要な役割を果たすことを明らかにした。さらに、電荷が伝導する際の損失も考慮した量子効率では、前記の光散乱を応用することにより、増感電極を薄膜化できることが分かった。

概要 （英文）

A comprehensive theoretical study of light scattering by TiO2 particles in dye-sensitized nanocrystalline photoelectrochemical cells is presented. First, a method for Monte Carlo simulation of light scattering in nanocrystalline films based on solutions of the Maxwell’s equations is proposed. A nanocrystalline film is assumed to be a superposition of randomly distributed nanoparticles and deviations of the nanocrystalline film from the randomness. Since the scattering field of the randomly and densely distributed nanoparticles can be neglected, the scattering field of the nanocrystalline film is the sum of scattering fields of the deviant parts in the nanocrystalline film. Configurations of the deviant parts are simulated with a random function of a computer language. A simulation converges in small number of the configuration patterns. The simulation theoretically demonstrates that almost all of the light incident to the nanocrystalline films in the photoelectrochemical solar cells penetrates without scattering. Second, light scattering by neighboring TiO2 particles in nanocrystalline films penetrated by electrolytes is examined based on rigorous solutions obtained by the T-matrix method. Scattering efficiencies are improved by agglomeration of particles much larger than the nanocrystalline particles. A cluster of relatively small particles among the large particles effectively scatters all incident light because of symmetrical scattering. On the other hand, the improvement of scattering efficiencies with clusters of optimal particles in terms of the efficiency is ascribed to significant forward scattering. Third, Monte Carlo simulations of light scattering by submicron TiO2 particles in dye-sensitized nanocrystalline electrodes are carried out. The Monte Carlo simulations reveal that the increase in absorption path length of photons in nanocrystalline films and optical confinement due to total reflection at solar cell surfaces remarkably improve the light absorption in the sensitized films. The contribution of optical confinement to the improvement is much greater than that of the increase in absorption path length. Finally, quantum efficiencies are calculated, considering the recombination of electrons in the nanocrystalline films. The application of light scattering improves the quantum efficiencies remarkably, especially for long-wavelength light. Optical confinement permits utilization of thinner sensitized films.

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