10:30 AM - *EQ09.04/EQ08.06.05
Ligand- and Cation-Exchanged Colloidal Quantum Dot Thin Films and Devices
University of Pennsylvania1
Colloidal quantum dots (QDs) are nanometer-scale crystals of inorganic semiconductors that are capped by organic or inorganic ligands. These QDs form an excellent, solution-processable materials class for thin-film electronics and optoelectronics. In this talk, I will describe and compare post-synthesis surface- and cation-exchange processes to engineer the optoelectronic properties QD thin films. In the first example, starting with electronically-coupled, thiocyanate-capped, wurtzite CdSe QD thin films, we use sequential cation exchange processes to substitute Cu+ for Cd2+ to realize Cu2Se nanocrystal thin-film intermediates. Subsequent partial cation exchange with the liquid-coordination-complex trioctylphosphine-indium chloride yields n-doped CuInSe2 NC thin films . These CuInSe2 nanocrystal films are used to form the channel of field-effect transistors (FETs), which upon Al2O3-encapsulation, are air-stable devices with high electron mobilities of ~10 cm2/Vs and current modulation of 105, comparable to those of high-performance Cd- and Pb-containing QD FETs. In the second example, we begin with epitaxially-fused PbSe QD thin films, and using sequential Cd+ and Cd2+ cation exchange, realize epitaxially-fused, zinc-blende CdSe QD films . We study the detrimental influence of Pb2+ impurities inherited from the starting QDs on the characteristics of CdSe QD FETs and how engineering of the device architecture can suppress these detrimental effects . We realize FETs with high electron mobilities of 35 cm2/Vs and current modulation of 106, after doping [2,3].
1. H. Wang, D. J. Butler, D. B. Straus, N. Oh, F. Wu, J. Guo, K. Xue, J. D. Lee, C. B. Murray, C. R. Kagan, “Air-Stable CuInSe2 Nanocrystal Transistors and Circuits via Post-Deposition Cation Exchange,” ACS Nano 13, 2324-2333 (2019).
2. Q. Zhao, G. Gouget, J. Guo, S. Yang, T. Zhao, D. B. Straus, C. Qian, N. Oh, H. Wang, C. B. Murray, C. R. Kagan, “Enhanced Carrier Transport in Strongly Coupled, Epitaxially Fused CdSe Nanocrystal Solids,” Nano Lett. 21. 3318-3324 (2021).
3. Q. Zhao, S. Yang, J. J. Ng, J. Xu, Y. C. Choi, C. B. Murray, C. R. Kagan, “Impurities in Nanocrystal Thin-Film Transistors Fabricated by Cation Exchange,” J. Phys. Chem Lett. 12, 6514-6518 (2021).