Chemical and Material Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States.
Nano Lett. 2011 Mar 9;11(3):1002-8. doi: 10.1021/nl103814g. Epub 2011 Feb 3.
The current-voltage (J-V) characteristics of ZnO/PbS quantum dot (QD) solar cells show a QD size-dependent behavior resulting from a Schottky junction that forms at the back metal electrode opposing the desirable diode formed between the ZnO and PbS QD layers. We study a QD size-dependent roll-over effect that refers to the saturation of photocurrent in forward bias and crossover effect which occurs when the light and dark J-V curves intersect. We model the J-V characteristics with a main diode formed between the n-type ZnO nanocrystal (NC) layer and p-type PbS QD layer in series with a leaky Schottky-diode formed between PbS QD layer and metal contact. We show how the characteristics of the two diodes depend on QD size, metal work function, and PbS QD layer thickness, and we discuss how the presence of the back diode complicates finding an optimal layer thickness. Finally, we present Kelvin probe measurements to determine the Fermi level of the QD layers and discuss band alignment, Fermi-level pinning, and the V(oc) within these devices.
ZnO/PbS 量子点 (QD) 太阳能电池的电流-电压 (J-V) 特性表现出与 QD 尺寸相关的行为，这是由于在与 ZnO 和 PbS QD 层之间形成理想二极管相反的背金属电极处形成肖特基结所致。我们研究了 QD 尺寸相关的滚降效应，这是指在正向偏压下光电流的饱和，以及当光和暗 J-V 曲线相交时发生的交叉效应。我们使用在 n 型 ZnO 纳米晶体 (NC) 层和 p 型 PbS QD 层之间形成的主二极管模型，与 PbS QD 层和金属接触之间形成的漏肖特基二极管串联，对 J-V 特性进行建模。我们展示了这两个二极管的特性如何取决于 QD 尺寸、金属功函数和 PbS QD 层厚度，并讨论了背二极管的存在如何使寻找最佳层厚度变得复杂。最后，我们进行了开尔文探针测量以确定 QD 层的费米能级，并讨论了这些器件中的能带排列、费米能级钉扎和 V(oc)。
