Ink discovery could lead to printable optoelectronic devices
2D black phosphorous ink brings large arrays of 2D material-based light sensors closer to reality
Research by scientists from Cambridge University, Imperial College London, Aalto University, Beihang University, and Zhejiang University has shown that 2D Black phosphorous is compatible with conventional inkjet printing techniques, with the potential to mass manufacture BP-based laser and optoelectronic devices.
Black phosphorus (BP) is a 2D material with unique optoelectronic properties. These include high carrier mobility (up to 50,000"‰cm2"‰V−1"‰s−1 in bulk at 30"‰K2) and a thickness-dependent direct bandgap, transitioning from ~0.3"‰eV in bulk to ~2"‰eV in mono-layer. These properties suggest potential applications in optoelectronics and photonics, in particular for the development of devices such as transistors, LEDs, photodetectors, solar cells and all-optical switches for ultrafast lasers
The interdisciplinary team, led by Tawfique Hasan of the Cambridge Graphene Centre, carefully optimised the chemical composition of BP to achieve a stable ink through the balance of complex and competing fluidic effects. This enabled the production of new functional laser and optoelectronic devices using high-speed printing.
Due to the BP ink drying rapidly, the final print quality of the devices made "“ a laser and a photodetector "“ is of a high quality and uniformity, and as good as what you would expect from the printing of a photograph onto paper.
The research titled 'Black phosphorus ink formulation for inkjet printing of optoelectronics and photonics' was published in Nature Communications and was funded by the Royal Academy of Engineering and the Engineering and Physical Sciences Research Council (EPSRC).
Guohua Hu, the lead author, said: "Our ink formulation enables highly uniform inkjet printing which does not degrade in the ambient environment, bringing large arrays of 2D material-based light sensors closer to reality.
"The formulation represents a significant scientific and technical achievement in terms of using this BP material for future applications. The functional ink, containing very small "˜flakes' of BP, allows us to print on a wide variety of substrates, including plastic, which remains stable for a prolonged period."
Meng Zhang from Beihang University led the work on printing BP-based non-linear optical devices which can be inserted easily into lasers to act as ultra-quick optical shutters. A continuous beam of laser radiation is converted into a repetitive series of very short bursts of light (or pulses) which is highly suited to industrial and medical applications, for example, machining, drilling, imaging and sensing.
"Our non-linear optical device design using BP achieves a significantly better performance and operational stability than any other previous demonstration," saidvZhang. "This is why our ink "˜recipe' using BP marks a significant step change towards new photonic devices and architectures using such a novel material."
As part of the research, the team also demonstrated the ability of BP to act as an efficient and highly-responsive detector of light, extending the wavelength range beyond what is currently achieved by conventional silicon-based photodetectors.
Tawfique Hasan, who leads the Hybrid Nanomaterials Engineering research group, added: "BP is a particularly interesting post-graphene material that offers many opportunities for new laser and optoelectronic devices. Yet despite its remarkable performance in the lab, practical real-world exploitation of this unique graphene-like crystal has been hindered by complex material fabrication and its poor environmental stability. But our breakthrough in BP ink is set to change all this and the ink itself can be seamlessly integrated with existing CMOS technologies."
