Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe2 NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films. First Cu+ is substituted for Cd2+ transforming CdSe NCs to Cu-rich Cu2Se NC films. Next, Cu2Se NC films are dipped into a Na2Se solution to Se-enrich the NCs, thus compensating the Cu-rich surface, promoting fusion of the Cu2Se NCs, and providing sites for subsequent In-dopants. The liquid-coordination-complex trioctylphosphine−indium chloride (TOP−InCl3) is used as a source of In3+ to partially exchange and n-dope CuInSe2 NC films. We fabricate FETs using CuInSe2 NC thin films and encapsulate the device by Atomic Layer Deposition (ALD). The elevated processing temperatures in the ALD provide in situ thermal activation of the In-dopants, while the encapsulation process further passivates trap states, improves doping efficiency, and makes the FETs air-stable. We demonstrate CuInSe2 NC FETs with linear (saturation) electron mobilities of 8.2 ± 1.8 cm2 /(V s) (10.5 ± 2.4 cm2 /(V s)) and with current modulation of 105 , comparable to that for high-performance Cd-, Pb-, and As-based NC FETs. We show the feasibility of CuInSe2 NC FETs for low-voltage operation and fabricate CuInSe2 NC inverters, demonstrating their promise for fabricating low-cost, low-toxicity integrated circuits.

Air-stable CuInSe2 nanocrystal transistors and circuits via post-deposition cation exchange

2019 Fall National Meeting

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