Air-stable n-type colloidal quantum dot solids

• Published in: Nature materials Vol. 13; no. 8; pp. 822 - 828
• Main Authors: Ning, Zhijun, Voznyy, Oleksandr, Pan, Jun, Hoogland, Sjoerd, Adinolfi, Valerio, Xu, Jixian, Li, Min, Kirmani, Ahmad R., Sun, Jon-Paul, Minor, James, Kemp, Kyle W., Dong, Haopeng, Rollny, Lisa, Labelle, André, Carey, Graham, Sutherland, Brandon, Hill, Ian, Amassian, Aram, Liu, Huan, Tang, Jiang, Bakr, Osman M., Sargent, Edward H.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.08.2014; Nature Publishing Group
• Subjects: 639/301/299; Air exposure; Biomaterials; Condensed Matter Physics; Electronics; Electronics industry; Energy conversion; Materials Science; Nanotechnology; Nitrogen dioxide; Optical and Electronic Materials; Oxidation; Photovoltaic cells; Quantum dots; Quantum physics; Semiconductors; Solar cells; Solar power; Solids; Solvents
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat4007

Colloidal quantum dots (CQDs) offer promise in flexible electronics, light sensing and energy conversion. These applications rely on rectifying junctions that require the creation of high-quality CQD solids that are controllably n-type (electron-rich) or p-type (hole-rich). Unfortunately, n-type semiconductors made using soft matter are notoriously prone to oxidation within minutes of air exposure. Here we report high-performance, air-stable n-type CQD solids. Using density functional theory we identify inorganic passivants that bind strongly to the CQD surface and repel oxidative attack. A materials processing strategy that wards off strong protic attack by polar solvents enabled the synthesis of an air-stable n-type PbS CQD solid. This material was used to build an air-processed inverted quantum junction device, which shows the highest current density from any CQD solar cell and a solar power conversion efficiency as high as 8%. We also feature the n-type CQD solid in the rapid, sensitive, and specific detection of atmospheric NO 2 . This work paves the way for new families of electronic devices that leverage air-stable quantum-tuned materials. Although several techniques have been reported to obtain electron-rich colloidal quantum dots, these materials usually suffer from poor stability under air exposure. It is now shown that the use of strongly bound ligands and a careful ligands-exchange strategy lead to air-stable n-type quantum dots that can be used in solar cells and chemical sensors.