CEISAM, Chimie Et Interdisciplinarité, Synthèse, Analyse, Modélisation, CNRS, UMR CNRS 6230, UFR des Sciences et des Techniques, 2, rue de la Houssinière - BP 92208, 44322 NANTES Cedex 3, France.
Nanoscale. 2017 Oct 19;9(40):15566-15575. doi: 10.1039/c7nr03698a.
Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are PbS QDs owing to their broad spectral absorption until long wavelengths, their easy processability and low cost. Here, we used control of the PbS QD size to understand charge transfer processes at the interfaces of a NiO semiconductor and explain the optimal QD size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 nm to 4 nm) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-ditert-butyl-2,2'-bipyridine) complex as a redox mediator. We found that PbS QDs with an average diameter of 3.0 nm show the highest performance in terms of efficient charge transfer and light harvesting efficiency. Our study showed that hole injection from the PbS QDs to the NiO valence band (VB) is an efficient process even with low injection driving force (-0.3 eV) and occurs in 6-10 ns. Furthermore we found that direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with a rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(iii) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes.
量子点 (QDs) 由于其高吸收系数、尺寸依赖性以及由于量子限制而易于调节其光学和电子特性，因此对于太阳能电池来说是非常有吸引力的材料。特别有趣的是 PbS QD，因为它们具有宽的光谱吸收，直到长波长，易于加工和低成本。在这里，我们通过控制 PbS QD 的尺寸来了解 NiO 半导体界面上的电荷转移过程，并解释光伏器件中最佳的 QD 尺寸。为此，我们合成了一系列不同直径（2.8nm 至 4nm）的 PbS QD，并通过时间分辨光谱研究了它们的电荷转移动力学，以及它们作为基于纳米晶 NiO 的太阳能电池敏化剂的能力，使用钴三（4,4'-二叔丁基-2,2'-联吡啶）络合物作为氧化还原介体。我们发现平均直径为 3.0nm 的 PbS QD 在有效电荷转移和光收集效率方面表现出最高的性能。我们的研究表明，即使注入驱动力较低（-0.3eV），从 PbS QD 到 NiO 价带 (VB) 的空穴注入也是一个有效的过程，发生在 6-10ns 之间。此外，我们发现直接电解质还原（光诱导电子转移到钴氧化还原介体）也与空穴注入平行发生，其速率常数具有相似的数量级（10-20ns）。尽管驱动力很大，但当 PbS 的直径增加时，PbS 被 Co(iii) 氧化猝灭的速率常数比在 NiO 上的空穴注入更急剧地减小。这被理解为增加限制电子转移的陷阱态的结果。我们相信，我们的详细发现将推进未来 QD 敏化光阴极的设计。
