Passivating violet phosphorus against ambient degradation for highly sensitive and long-term stable optoelectronic devices

Recent success in exfoliating violet or Hittorf's phosphorus down to monolayer reignites the research passion in this ancient yet mysterious material, questing for superior electronic and optoelectronic functionalities. Unfortunately, the poor air stability that plagues black phosphorus also exists in the violet counterpart. Aiming to provide more insight into the degradation chemistry and accordingly find a facile solution for it, herein, we employ concerted elemental, chemical and vibrational spectroscopies to reveal the critical role of oxygen and water in the degradation mechanism and pathway of violet phosphorus in ambient condition. Thereafter, a simple passivation approach by oxide encapsulation is demonstrated to realize air-stable violet phosphorus photodetector device. As the proof-of-concept, the photodetector fabricated accordingly shows superior figures of merit with ultralow dark current (< 10−13 A), high low-light responsivity (6 A W−1) and fast response time (< 10 ms) in the ultraviolet to visible spectrum, as well as great chemical robustness against harsh environments.