Reid Obadiah G, Munechika Keiko, Ginger David S
Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA.
Nano Lett. 2008 Jun;8(6):1602-9. doi: 10.1021/nl080155l. Epub 2008 May 1.
We describe local (~150 nm resolution), quantitative measurements of charge carrier mobility in conjugated polymer films that are commonly used in thin-film transistors and nanostructured solar cells. We measure space charge limited currents (SCLC) through these films using conductive atomic force microscopy (c-AFM) and in macroscopic diodes. The current densities we measure with c-AFM are substantially higher than those observed in planar devices at the same bias. This leads to an overestimation of carrier mobility by up to 3 orders of magnitude when using the standard Mott-Gurney law to fit the c-AFM data. We reconcile this apparent discrepancy between c-AFM and planar device measurements by accounting for the proper tip-sample geometry using finite element simulations of tip-sample currents. We show that a semiempirical scaling factor based on the ratio of the tip contact area diameter to the sample thickness can be used to correct c-AFM current-voltage curves and thus extract mobilities that are in good agreement with values measured in the conventional planar device geometry.
我们描述了对共轭聚合物薄膜中电荷载流子迁移率进行的局部（分辨率约为150纳米）定量测量，这种共轭聚合物薄膜常用于薄膜晶体管和纳米结构太阳能电池。我们使用导电原子力显微镜（c-AFM）并在宏观二极管中测量通过这些薄膜的空间电荷限制电流（SCLC）。我们用c-AFM测量的电流密度在相同偏压下比平面器件中观察到的电流密度高得多。当使用标准的莫特-格尼定律拟合c-AFM数据时，这会导致载流子迁移率被高估多达3个数量级。我们通过使用尖端-样品电流的有限元模拟来考虑适当的尖端-样品几何形状，从而协调了c-AFM和平面器件测量之间的这种明显差异。我们表明，基于尖端接触面积直径与样品厚度之比的半经验比例因子可用于校正c-AFM电流-电压曲线，从而提取出与在传统平面器件几何形状中测量的值高度一致的迁移率。
