Plastic electronics represents a fast-advancing research field that has the potential to change the way we live. The first applications which are beginning to emerge focus on low-cost, high-volume ‘flexible’ and large-area electronics – such as light and bendable displays or cheap solar cells that can be easily put on any shapes of surfaces. Looking further, this technology can also span the areas of solid-state lighting, imaging and sensing, medical diagnostics, photonics and communications.
In addition to the organic semiconductors which have already established their firm footing as the light emitting materials in OLEDs, oxides and some inorganic materials are becoming key players in the field of plastic electronics due to their excellent qualities such as higher charge carrier mobility, environmental stability, non-toxicity, and – for some – optical transparency. The latter can take plastic electronics to another level, turning it into ‘transparent electronics’.
Another advantage of plastic electronics is its low-cost manufacture, which makes it a more level playing field, consequently attracting a great number of researchers to pour their talent and effort into advancing this field. This economic consideration along with the adolescence stage of development also means that there are opportunities for countries like Thailand to jump in and join the advancement of the area which is expected to be worth billions of dollars in the near future.
A pseudohalide inorganic material, copper (I) thiocyanate or CuSCN, with a wide band gap (larger than 3.5 eV) and excellent hole transport properties (with a hole mobility between 0.01 to 0.1 cm2 V-1 s-1) has recently been demonstrated as a new candidate for a transparent p-type semiconductor.
Thin-film transistors and simple logic gates are fabricated using the simple solution-based spin-coating method. Devices show excellent characteristics of a p-type transistor and a p-type unipolar NOT gate. The unique combination of excellent transparency and hole-transporting properties would allow the realization of complementary logic circuits by pairing with the already-available n-type oxides such as ZnO or In2O3, which would in turn lead to transparent electronics.
Furthermore, when incorparting CuSCN as a hole-transport layer (HTL) in OLEDs and OPVs, significant efficiency improvements have been demonstrated. This is again due to the unique optical and electronic properties of this material.
In OLEDs, the electronic energy levels of CuSCN are well matched with those of other components, resulting in a low injection energy barrier for holes while creating a large energy barrier for electron blocking. This leads to OLEDs that turns on at a lower volage and shows smaller leakage current.
As for OPVs, the excellent optical transparency of CuSCN allows more light to reach the light-abosbing layer, and hence more light-to-current conversion, i.e., a solar cell with higher efficiency.