Assessing the role of plasma-engineered acceptor-like intra- and inter-grain boundaries of heterogeneous WS2–WO3 nanosheets for photocurrent characteristics

Abstract

High-temperature annealing in tungsten disulfide resulted in heterogeneous WS₂–WO₃ in which intra- (within WS₂ and WO₃) and inter- (between WS₂ and WO₃) grain boundaries were observed, which were highly critical for charge transport and recombination. The heterogeneous WS₂–WO₃ phase was evidenced by observing the coexistence of d-spacing values of 0.26 nm (WS₂) and 0.37 nm (WO₃) in transmission electron microscopic (TEM) studies. Further systematic high-resolution TEM studies elucidated that intra-grain boundaries separated crystallites within WS₂ and WO₃, while inter-grain boundaries separated WS₂ from WO₃. As WS₂ and WO₃ are both n-type, these defects are acceptor-like in the grain boundaries and they actively participate in the capture (trapping) process, which impedes charge transport characteristics in the heterogeneous WS₂–WO₃ films. Plasma treatment in the heterogeneous WS₂–WO₃ film, for 60 minutes using argon, energetically modulated the defects in the intra/inter-grain boundaries, as evidenced from detailed comparative photocurrent characteristics obtained individually in (i) pristine WS₂, (ii) heterogeneous WS₂–WO₃ and (iii) Ar plasma-treated heterogeneous WS₂–WO₃ films under blue and green lasers, along with AM1.5 (1 sun) illumination. Detrimental roles (trapping/de-trapping and scattering) of grain boundary states on photoelectrons were seen to be significantly suppressed under the influence of plasma.