Water‐Catalyzed Oxidation of Few‐Layer Black Phosphorous in a Dark Environment

Abstract

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices.

Role of Water and Defects in Photo‐Oxidative Degradation of Methylammonium Lead Iodide Perovskite

“…As a H 2 O approaches the O 2 , the energy levels of π* 2p of O 2 are lowered and get closer to the valence bands of MAPbI 3 (Figure ). The strong polarization effect of water can increase the electron affinity of oxygen, causing the reduction of O 2 energy levels . Especially at hollow site on PbI 2 ‐terminated surface, the reducing of O 2 energy levels is particularly significant.…”

Intrinsic Correlation between Electronic Structure and Degradation: From Few‐Layer to Bulk Black Phosphorus

“…In the dark, there are no physical phenomena such as the photogeneration of carriers and surface photovoltaic effects.I no ther words,t he degradation mechanisms in the dark are connected to the intrinsic properties of BP.Inthis context, Hu and co-workers recently demonstrated that H 2 Om olecules catalyze the oxidation of BP. [24] They showed that H 2 Omolecules pull the energy level of the O 2 molecules towards the CB of BP through the polarization effect of H 2 O. As BP degradation results from the interaction between BP and O 2 /H 2 Om olecules,t he degradation can be explained by the interfacial energetics between BP and O 2 /H 2 Om olecules.I ts hould be noted that the interfacial energetics between BP and these molecules depend highly on the number of layers of BP owing to the layer-dependent electronic structure of BP.T ot horoughly understand this layer dependence of degradation, the number of layers and the physical properties that can be used to follow the degradation should be simultaneously studied.…”

Midinfrared Electro-optic Modulation in Few-Layer Black Phosphorus

“…Although the chemical stability of black phosphorus is a concern as it reacts with water and oxygen and quickly degrades when exposed to air 27,28 , BP can be passivated or concealed 29,30 , after which the BP devices can be preserved over a very long time without discernible degradation in device performance.…”