Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
J Phys Chem A. 2010 Mar 11;114(9):3127-38. doi: 10.1021/jp908747z.
We have devised dye-sensitized solar cells (DSSCs) with >6% efficiency by employing composite photoanodes of SnO(2) nanoparticles/ZnO nanotetrapods. Benefiting from material advantages of both constituents, the composite photoanodes exhibit extremely large roughness factors, good charge collection, and tunable light scattering properties. Among the three composite photoanodes with widely differing compositions tested, the best performance (efficiency = 6.31%) was obtained with a weight ratio of SnO(2)/ZnO 2:1 mainly due to the highest saturated J(sc) achieved at a thinnest film thickness. Charge collection losses in composite films with more ZnO nanotetrapods content and thus necessarily larger film thicknesses appear to be a main limiting factor on IPCE and therefore J(sc), which undermines the gain from their favorable light scattering ability. An ultrathin layer of ZnO spontaneously shelled on SnO(2) nanoparticles is found to enhance V(oc) primarily by lifting the band edges rather than by suppressing recombination. Finally, by intensity modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS), we have identified that recombination in SnO(2)/ZnO composite films is mainly determined by the ZnO shell condition on SnO(2), whereas electron transport is greatly influenced by the morphologies and sizes of the ZnO crystalline additives. In particular, ZnO nanotetrapods have proved to be superior in electron transport and therefore charge collection over ZnO particles additives in the SnO(2)/ZnO composite-based DSSCs.
我们设计了染料敏化太阳能电池（DSSCs），其效率超过 6%，方法是采用 SnO(2)纳米颗粒/ZnO 纳米四脚架复合材料的光电阳极。得益于两种成分的材料优势，复合光电阳极具有极高的粗糙度因子、良好的电荷收集能力和可调谐的光散射特性。在所测试的三种组成成分差异很大的复合光电阳极中，SnO(2)/ZnO 重量比为 2:1 的复合光电阳极表现出最佳性能（效率=6.31%），主要是因为在最薄的薄膜厚度下达到了最高的饱和 J(sc)。具有更多 ZnO 纳米四脚架含量的复合膜中的电荷收集损耗，以及因此不可避免的更大的膜厚度，似乎是 IPCE 因此也是 J(sc)的主要限制因素，这削弱了它们有利的光散射能力带来的收益。发现 SnO(2)纳米颗粒上自发形成的 ZnO 超薄层主要通过提升能带边缘来提高 V(oc)，而不是通过抑制复合来提高 V(oc)。最后，通过强度调制光电流/光电压光谱法（IMPS/IMVS），我们确定 SnO(2)/ZnO 复合膜中的复合主要取决于 SnO(2)上 ZnO 壳的状态，而电子传输则受 ZnO 晶体添加剂的形态和尺寸的极大影响。特别是 ZnO 纳米四脚架已被证明在电子传输方面优于 ZnO 颗粒添加剂，因此在基于 SnO(2)/ZnO 复合的 DSSCs 中，在电荷收集方面也优于 ZnO 颗粒添加剂。
