Abstract
Black phosphorus is a two-dimensional material of great interest, in part because of its high carrier mobility and thickness dependent direct bandgap. However, its instability under ambient conditions limits material deposition options for device fabrication. Here we show a black phosphorus ink that can be reliably inkjet printed, enabling scalable development of optoelectronic and photonic devices. Our binder-free ink suppresses coffee ring formation through induced recirculating Marangoni flow, and supports excellent consistency (< 2% variation) and spatial uniformity (< 3.4% variation), without substrate pre-treatment. Due to rapid ink drying (< 10 s at < 60 °C), printing causes minimal oxidation. Following encapsulation, the printed black phosphorus is stable against long-term (> 30 days) oxidation. We demonstrate printed black phosphorus as a passive switch for ultrafast lasers, stable against intense irradiation, and as a visible to near-infrared photodetector with high responsivities. Our work highlights the promise of this material as a functional ink platform for printed devices.
Highlights
Black phosphorus is a two-dimensional material of great interest, in part because of its high carrier mobility and thickness dependent direct bandgap
The choice of solvent is key to achieving effective exfoliation and stable dispersions, since ultrasound-assisted liquid phase exfoliation (UALPE) is reliant on optimising the intermolecular interactions with the Black phosphorus (BP) flakes to minimise the enthalpy of mixing[28,29,30]
Among the three organic solvents we investigate for UALPE, through atomic-force microscopy (AFM), optical absorption and light scattering, we demonstrate that NMP is the most effective solvent for BP exfoliation
Summary
Black phosphorus is a two-dimensional material of great interest, in part because of its high carrier mobility and thickness dependent direct bandgap. A high boiling point can lead to long drying times when depositing the BP dispersions, resulting in significant oxidation and preventing the fabrication of stable devices under ambient conditions[1, 3, 19]. Unlike solvents, binders form an integral part of the printed film, and must be removed through high temperature annealing[12, 13, 26] or intense pulsed light[27] to retain the functionalities of the 2d materials for optoelectronic and photonic devices This approach is impractical here since these processes will likely lead to BP oxidation while exposed to ambient conditions. Combining the printing consistency and uniformity, this long-term stability allows us to develop robust photonic and optoelectronic devices using printed BP, including a saturable absorber (SA) for stable a Intensity (a.u.)
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