Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density.,Nano Letters

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Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density.
Nano Letters ( IF 9.6 ) Pub Date : 2020-04-06 , DOI: 10.1021/acs.nanolett.0c00638
Bin Sun ₁ , Maral Vafaie ₁ , Larissa Levina ₁ , Mingyang Wei ₁ , Yitong Dong ₁ , Yajun Gao ₂ , Hao Ting Kung ₃ , Margherita Biondi ₁ , Andrew H Proppe _{1,

4} , Bin Chen ₁ , Min-Jae Choi ₁ , Laxmi Kishore Sagar ₁ , Oleksandr Voznyy ₁ , Shana O Kelley _{4,

5} , Frédéric Laquai ₂ , Zheng-Hong Lu ₃ , Sjoerd Hoogland ₁ , F Pelayo García de Arquer ₁ , Edward H Sargent ₁

Affiliation

Increasing the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells has relied on improving the passivation of CQD surfaces, enhancing CQD coupling and charge transport, and advancing device architecture. The presence of hydroxyl groups on the nanoparticle surface, as well as dimers-fusion between CQDs-has been found to be the major source of trap states, detrimental to optoelectronic properties and device performance. Here, we introduce a CQD reconstruction step that decreases surface hydroxyl groups and dimers simultaneously. We explored the dynamic interaction of charge carriers between band-edge states and trap states in CQDs using time-resolved spectroscopy, showing that trap to ground-state recombination occurs mainly from surface defects in coupled CQD solids passivated using simple metal halides. Using CQD reconstruction, we demonstrate a 60% reduction in trap density and a 25% improvement in charge diffusion length. These translate into a PCE of 12.5% compared to 10.9% for control CQDs.

中文翻译：

胶体量子点的配体辅助重建可降低陷阱态密度。

胶体量子点（CQD）太阳能电池的功率转换效率（PCE）的提高依赖于改善CQD表面的钝化，增强CQD耦合和电荷传输以及推进器件架构。已经发现纳米颗粒表面上羟基的存在以及CQD之间的二聚体-融合是陷阱态的主要来源，这不利于光电性能和器件性能。在这里，我们介绍了一个CQD重建步骤，该步骤可同时减少表面羟基和二聚体。我们使用时间分辨光谱学研究了CQDs的带边态和陷阱态之间的载流子的动态相互作用，表明陷阱到基态的重组主要是由简单的金属卤化物钝化的耦合CQD固体中的表面缺陷引起的。使用CQD重建，我们证明了陷阱密度降低了60％，电荷扩散长度提高了25％。与对照CQD的10.9％相比，这意味着PCE为12.5％。

更新日期：2020-03-31

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