Air-Stable CuInSe₂ Nanocrystal Transistors and Circuits via Post-Deposition Cation Exchange

Abstract

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 demonstrate Al2O3-encapsulated, air-stable 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. The CuInSe2 NC FETs are used as building blocks of integrated inverters to demonstrate their promise for low-cost, low-toxicity NC circuits.

Solution-processable integrated CMOS circuits based on colloidal CuInSe2 quantum dots

“…4c ). The latter is considerably higher compared to values demonstrated previously for an all-NFET inverter made of fused CuInSe 2 CQDs ( G < 2) 48 and is comparable to gain reported for a CMOS inverter made of PbSe CQDs ( G ≈ 14) 37 .…”

“…Due to their narrow bandgap (composition tunable between 1 and 1.5 eV in the bulk form), they are excellent sunlight harvesters that have been extensively explored in the context of applications in PVs 33 , 44 and luminescent solar concentrators 47 . Several recent works have also investigated charge-transport properties of CuInSe x S 2− x CQDs from the standpoint of prospective applications in electronic devices 48 – 50 . These studies have revealed a considerable effect of internal native defects on electrical conductance not observable in PbSe(S) and CdSe CQDs.…”

Self-assembly for electronics

“…Cdand Pb-free NP compositions are similarly being developed to construct electronic devices and circuits. 54,55 Also in these examples, the chemical and thermal processes were selected to be compatible with device fabrication on flexible plastics, 56 as needed for wearable and implantable devices.…”

Luminescent Photonic Crystals with Extreme‐UV Bandgaps Made of CuInSe2 Quantum Dots

“…Recently, there have been increasing interest in the CuInSe 2 NCs, [ 14 ] which have wide applications in solar cells, [ 15–17 ] photodetectors, [ 18–20 ] and transistors. [ 21 ] The CuInSe 2 /CuInS 2 , CuInSe 2 /(CuInSe x S 1− x ) 5 /CuInS 2 , and CuInSe x S 2− x /ZnS NCs can be used for photoelectrochemical hydrogen generation. [ 22–24 ] On the other hand, the implementation of the optoelectronic devices often relies on another critical component: photonic crystals (PhCs).…”