Pingree Liam S C, Reid Obadiah G, Ginger David S
Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA.
Nano Lett. 2009 Aug;9(8):2946-52. doi: 10.1021/nl901358v.
We use photoconductive atomic force microscopy to image nanoscale spatial variations in photocurrent across the surfaces of photovoltaic cells made from blends of the conjugated polymer regioregular poly(3-hexylthiopene) (P3HT) with phenyl-C(61)-butyric acid methyl ester (PCBM). We study how the spatial variations in photocurrent evolve with thermal annealing, and we correlate these changes with the evolution of macroscopic film and device properties such as external quantum efficiency and carrier mobility. We use conductive atomic force microscopy to examine the development of injection and transport networks for both electrons and holes as a function of annealing. We find that the hole transport, electron transport, and photocurrent collection networks become increasingly heterogeneous with thermal annealing and remain heterogeneous on the 10-100 nm length scale even in the most efficient P3HT/PCBM devices. After annealing, the regions of the greatest dark hole currents, greatest dark electron currents, and greatest photocurrents are each associated with different regions of the nanostructured films. These results suggest spatial heterogeneity can contribute to the imperfect internal quantum efficiency even in relatively efficient organic photovoltaics and that fully 3D modeling is needed to describe the devices physics of polymer blend solar cells.
我们使用光电导原子力显微镜对由共轭聚合物区域规整聚（3-己基噻吩）（P3HT）与苯基-C61-丁酸甲酯（PCBM）的共混物制成的光伏电池表面的光电流纳米级空间变化进行成像。我们研究光电流的空间变化如何随热退火而演变，并将这些变化与宏观薄膜和器件特性（如外量子效率和载流子迁移率）的演变相关联。我们使用导电原子力显微镜来研究作为退火函数的电子和空穴的注入和传输网络的发展。我们发现，随着热退火，空穴传输、电子传输和光电流收集网络变得越来越不均匀，即使在最有效的P3HT/PCBM器件中，在10-100nm长度尺度上仍然不均匀。退火后，最大暗空穴电流、最大暗电子电流和最大光电流的区域分别与纳米结构薄膜的不同区域相关联。这些结果表明，即使在相对高效的有机光伏器件中，空间不均匀性也可能导致内部量子效率不完善，并且需要完整的三维建模来描述聚合物共混太阳能电池的器件物理。
