Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density

Bin Sun, Maral Vafaie, Larissa Levina, Mingyang Wei, Yitong Dong, Yajun Gao, Hao Ting Kung, Margherita Biondi, Andrew H. Proppe, Bin Chen, Min-Jae Choi, Laxmi Kishore Sagar, Oleksandr Voznyy, Shana O. Kelley, Frédéric Laquai, Zhenghong Lu, Sjoerd Hoogland, F Pelayo García de Arquer, E. Sargent

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

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.
Original languageEnglish (US)
Pages (from-to)3694-3702
Number of pages9
JournalNano Letters
Volume20
Issue number5
DOIs
StatePublished - Mar 31 2020

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