Thin-film transistors made from solution-processed semiconductors are promising alternatives to traditional silicon-based complementary metal-oxide-semiconductor (CMOS) devices that normally need to be fabricated using expensive and complicated vacuum processes.

A team led by Dmitri Talapin has made high-performance cadmium selenide nanocrystal field-effect transistors in a solution-processing technique that have charge-carrier mobilities as high as over 400 cm2/(V s). This value is comparable to those of traditional, crystalline silicon-based semiconductors. What's more, the nanocrystal FETs are robust and have high-megahertz switching speeds, which makes them useful for a range of high-performance electronic and optoelectronic device applications.

Nanocrystal soldering

The researchers made their devices by spin-coating colloidal solutions of CdSe nanocrystals capped with molecular solders made from Na2Cd2Se3 onto various oxide gate dielectrics. They then thermally annealed the nanocrystals formed on the dielectrics at different temperatures to find out where the outstanding carrier mobilities in the finished FETs come from.

According to the team, gate dielectrics made from ZrOx, for example, provide a good surface for the charge transport of [Cd2Se3]2--capped CdSe nanocrystals because they contain fewer localized charge traps. As a result, the FETs produced have carrier mobilities as high as 200–450 cm2/(V s), depending on the temperature at which the nanocrystals have been annealed.

Applications in displays, solution-processed solar cells and thermoelectric devices

As for applications, the FETs might be used in portable electronics, says Talapin, and the devices could drive display pixels, for example.

“Our work is an important step forward when it comes to developing high-performance electronic and optoelectronic devices using a low-cost solution process while retaining electronic properties comparable to those of traditional, crystalline semiconductors.

“And that is not all: our chemistry can also be applied to different II-VI and III-V semiconductors,” he tells, “and we now plan to apply the concept of nanocrystal soldering to devices where enhanced charge transport can be combined with advanced optical and thermoelectric properties. In particular, we are working on solution-processed solar cells and thermoelectric devices.”

The research is detailed in Nano Letters DOI: 10.1021/acs.nanolett.5b01258.