National Renewable Energy Laboratory, Golden, Colorado 80401-3393, United States.
Nano Lett. 2014 May 14;14(5):2305-9. doi: 10.1021/nl4046087. Epub 2014 Apr 23.
Understanding the influence of different film structures on electron diffusion in nanoporous metal oxide films has been challenging. Because of the rate-limiting role that traps play in controlling the transport properties, the structural effects of different film architectures are largely obscured or reduced. We describe a general approach to probe the impact of structural order and disorder on the charge-carrier dynamics without the interference of transport-limiting traps. As an illustration of this approach, we explore the consequences of trap-free diffusion in vertically aligned nanotube structures and random nanoparticle networks in sensitized titanium dioxide solar cells. Values of the electron diffusion coefficients in the nanotubes approached those observed for the single crystal and were up to 2 orders of magnitude greater than those measured for nanoparticle films with various average crystallites sizes. Transport measurements together with modeling show that electron scattering at grain boundaries in particle networks limits trap-free diffusion. In presence of traps, transport was 10(3)-10(5) times slower in nanoparticle films than in the single crystal. Understanding the link between structure and carrier dynamics is important for systematically altering and eventually controlling the electronic properties of nanoscaled materials.
理解不同薄膜结构对纳米多孔金属氧化物薄膜中电子扩散的影响具有挑战性。由于陷阱在控制输运性质方面起着限速作用，因此不同薄膜结构的结构效应在很大程度上被掩盖或减弱。我们描述了一种通用方法，可以在没有传输限制陷阱干扰的情况下探测结构有序和无序对载流子动力学的影响。作为这种方法的说明，我们研究了在敏化二氧化钛太阳能电池中垂直排列的纳米管结构和无陷阱扩散的随机纳米颗粒网络中，结构有序和无序对载流子动力学的影响。在纳米管中观察到的电子扩散系数接近单晶的扩散系数，比具有不同平均晶粒尺寸的纳米颗粒薄膜的扩散系数高 2 个数量级。传输测量和建模表明，在颗粒网络中，电子在晶粒边界处的散射限制了无陷阱扩散。在存在陷阱的情况下，纳米颗粒薄膜中的传输速度比单晶中的传输速度慢 10(3)-10(5)倍。理解结构和载流子动力学之间的联系对于系统地改变并最终控制纳米材料的电子性质非常重要。
