Deparis O, Mouchet S R, Su B-L
Solid-State Physics Laboratory, University of Namur, 61 rue de Bruxelles, B-5000 Namur, Belgium.
Laboratory of Inorganic Materials Chemistry (CMI), University of Namur, 61 rue de Bruxelles, B-5000 Namur, Belgium.
Phys Chem Chem Phys. 2015 Nov 11;17(45):30525-32. doi: 10.1039/c5cp04983k.
Light harvesting enhancement by slow photons in photonic crystal catalysts or dye-sensitized solar cells is a promising approach for increasing the efficiency of photoreactions. This structural effect is exploited in inverse opal TiO2 photocatalysts by tuning the red edge of the photonic band gap to the TiO2 electronic excitation band edge. In spite of many experimental demonstrations, the slow photon effect is not fully understood yet. In particular, observed enhancement by tuning the blue edge has remained unexplained. Based on rigorous couple wave analysis simulations, we quantify light harvesting enhancement in terms of absorption increase at a specific wavelength (monochromatic UV illumination) or photocurrent increase (solar light illumination), with respect to homogeneous flat slab of equivalent material thickness. We show that the commonly accepted explanation relying on light intensity confinement in high (low) dielectric constant regions at the red (blue) edge is challenged in the case of TiO2 inverse opals because of the sub-wavelength size of the material skeleton. The reason why slow photons at the blue edge are also able to enhance light harvesting is the loose confinement of the field, which leads to significant resonantly enhanced field intensity overlap with the skeleton in both red and blue edge tuning cases, yet with different intensity patterns.
在光子晶体催化剂或染料敏化太阳能电池中，利用慢光子增强光捕获是提高光反应效率的一种很有前景的方法。通过将光子带隙的红边调谐到TiO₂电子激发带边，这种结构效应被应用于反蛋白石TiO₂光催化剂中。尽管有许多实验证明，但慢光子效应尚未得到充分理解。特别是，通过调谐蓝边观察到的增强现象仍然无法解释。基于严格耦合波分析模拟，我们根据等效材料厚度的均匀平板，在特定波长（单色紫外光照射）下的吸收增加或光电流增加（太阳光照射）来量化光捕获增强。我们表明，由于材料骨架的亚波长尺寸，在TiO₂反蛋白石的情况下，依赖于红（蓝）边高（低）介电常数区域中光强限制的普遍接受的解释受到了挑战。蓝边慢光子也能够增强光捕获的原因是场的松散限制，这导致在红边和蓝边调谐情况下，场强度与骨架都有显著的共振增强重叠，但强度模式不同。
