Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime
Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime
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DOI：
10.1038/ncomms4803
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发表时间：
2014-05
影响因子：
16.6
通讯作者：
D. Zhitomirsky;O. Voznyy;L. Levina;S. Hoogland;Kyle W. Kemp;Alexander H. Ip;S. Thon;E. Sargent
中科院分区：
文献类型：
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作者：
D. Zhitomirsky;O. Voznyy;L. Levina;S. Hoogland;Kyle W. Kemp;Alexander H. Ip;S. Thon;E. Sargent
胶体量子点是一种高效、低成本和易于实现溶液处理光电子器件的有吸引力的材料。尽管新型量子点固体的迁移率（1-30 cm 2 V-1 s-1）令人印象深刻，但令人惊讶的是，迁移率低得多（10 - 3-10 - 2cm 2 V-1 s-1）的固体产生了最好的光伏性能。在这里，我们表明，它不是流动性，而是复合中心之间的平均间距，支配今天的量子点固体中的电荷的扩散长度。在这种情况下，胶体量子点膜不会受益于电荷载流子迁移率的进一步改善。我们开发了一个器件模型，准确地预测器件的厚度依赖性和扩散长度依赖性。直接扩散长度测量表明固态配体交换过程是有害重组中心的潜在来源。然后，我们提出了一种新的途径，在溶液中的钝化与紧密结合的氯硫醇，保持钝化从溶液到薄膜，实现了8.5%的功率转换效率。
Colloidal quantum dots are attractive materials for efficient, low-cost and facile implementation of solution-processed optoelectronic devices. Despite impressive mobilities (1–30 cm2V−1s−1) reported for new classes of quantum dot solids, it is—surprisingly—the much lower-mobility (10−3–10−2cm2V−1s−1) solids that have produced the best photovoltaic performance. Here we show that it is not mobility, but instead the average spacing among recombination centres that governs the diffusion length of charges in today’s quantum dot solids. In this regime, colloidal quantum dot films do not benefit from further improvements in charge carrier mobility. We develop a device model that accurately predicts the thickness dependence and diffusion length dependence of devices. Direct diffusion length measurements suggest the solid-state ligand exchange procedure as a potential origin of the detrimental recombination centres. We then present a novel avenue for in-solution passivation with tightly bound chlorothiols that retain passivation from solution to film, achieving an 8.5% power conversion efficiency.