高效率PbS量子点太阳能电池的性能演变与配体氧化
Ligand Dependent Oxidation Dictates the Performance Evolution of High Efficiency PbS Quantum Dot Solar Cells
摘要：
硫化铅（PbS）量子点（QD）光致发光材料已经达到了令人印象深刻的12%的效率，使它们在未来的应用中特别有前途。与许多其他类型的新兴光伏器件一样，它们的环境不稳定性仍然是这项技术的致命弱点。在这项工作中，我们证明了暴露于含氧环境中的PbS量子点的降解过程与配体的选择密切相关，而不是它们的固有特性。特别是，我们证明，虽然1，2-乙二硫醇（EDT）配体导致显着的氧化的PbS，碘化铅/溴化铅（PbX 2）涂覆的PbS量子点没有显示氧化或降解的迹象。因此，由于前者普遍用作QD太阳能电池中的空穴提取层，因此它主要负责器件性能的演变。EDT-PbS量子点的氧化导致有效量子点尺寸显著减小，这引发了两个竞争过程：增强电子阻挡的改进的能量对准，但降低了通过层的电荷传输。在早期，前一个过程占主导地位，导致通常报告的，但到目前为止还没有完全解释的性能的初始增加，而后者支配的光伏性能的退化和恶化的开始。我们的工作突出了PbS量子点太阳能电池的稳定性可以通过适当选择所有器件组件的配体来显著增强。
英文摘要：
Lead sulfide (PbS) quantum dot (QD) photovoltaics have reached impressive efficiencies of 12%, making them particularly promising for future applications. Like many other types of emerging photovoltaic devices, their environmental instability remains the Achilles heel of this technology. In this work, we demonstrate that the degradation processes in PbS QDs which are exposed to oxygenated environments are tightly related to the choice of ligands, rather than their intrinsic properties. In particular, we demonstrate that while 1,2-ethanedithiol (EDT) ligands result in significant oxidation of PbS, lead iodide/lead bromide (PbX2) coated PbS QDs show no signs of oxidation or degradation. Consequently, since the former is ubiquitously used as a hole extraction layer in QD solar cells, it is predominantly responsible for the device performance evolution. The oxidation of EDT-PbS QDs results in a significantly reduced effective QD size, which triggers two competing processes: improved energetic alignment that enhances electron blocking, but reduced charge transport through the layer. At early times, the former process dominates, resulting in the commonly reported, but so far not fully explained initial increase in performance, while the latter governs the onset of degradation and deterioration of the photovoltaic performance. Our work highlights that the stability of PbS quantum dot solar cells can be significantly enhanced by an appropriate choice of ligands for all device components.
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