Solution-Based Property Tuning of Black Phosphorus

The air instability of black phosphorus (BP) severely hinders the development of its electronic and optoelectronic applications. Although a lot of effort has been made to passivate it against degradation in ambient conditions, approaches to further manipulate the properties of passivated BP are still very limited. Herein, we report a simple and low-cost chemical method that can achieve BP passivation and property tailoring simultaneously. The method is conducted by immersing a BP sample in the solution containing both 2,2,6,6-tetramethylpiperidinyl- N-oxyl (TEMPO) and triphenylcarbenium tetrafluorobor in a mixture of water and acetone (v/v = 1:1). After the treatment, the BP sample is functionalized with TEMPO, which not only efficiently passivates BP but also p-dopes BP to a degenerated density level of 10¹³ cm^-2. The performance of the BP field effect transistor is improved after functionalization with a high I_on/ I_off ratio of 10⁶ and carrier mobility of 881.5 cm²/(V·s). The functionalization-induced doping also significantly reduces the contact resistance between BP and the Cr/Au electrode to 0.97 kΩ·μm. Additionally, we observe a great reduction of BP electrical and optical anisotropies after functionalization. This chemical functionalization method provides a viable route to simultaneously passivate and tune the properties of BP.