Notre Dame Radiation Laboratory, and Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
Proc Natl Acad Sci U S A. 2011 Jan 4;108(1):29-34. doi: 10.1073/pnas.1011972107. Epub 2010 Dec 13.
Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.
量子点-金属氧化物结是下一代太阳能电池、发光二极管和纳米结构电子阵列的重要组成部分。在这里，我们使用一系列 CdSe 量子点供体（直径分别为 2.8、3.3、4.0 和 4.2nm）和金属氧化物纳米颗粒受体（SnO2、TiO2 和 ZnO）对这些结处的电子转移进行了全面研究。表观电子转移速率常数强烈依赖于系统自由能的变化，在小驱动力下急剧上升，然后在远离特征重组能的情况下适度上升。观察到的趋势模仿了从单个量子态到金属氧化物纳米颗粒导带中存在的电子接受态连续体的电子转移的预测行为。与染料敏化金属氧化物电子转移研究不同，由于电子冷却速率与电子转移速率的相对较大比值，我们的系统没有表现出非热化的热电子注入。为了研究这些发现对光伏电池的影响，以与研究中电子转移部分相同的方式构建了量子点-金属氧化物工作电极。有趣的是，表现出最快电子转移速率（SnO2）的薄膜与显示出最高光电流（TiO2）的薄膜并不相同。这些发现表明，除了量子点-金属氧化物界面处的电子转移外，其他电子转移反应在确定整体器件效率方面起着关键作用。
