A potential approach to grow van der Waals heterostructures based on pulsed laser deposition of solid oxide precursors for thin film photovoltaics

Description

Rapid development of photovoltaic power industry has pushed an active search for new materials for photovoltaics and photodetection, where heterostructures with an efficient charge-carrier separation are of particular interest. Emerging van der Waals heterostructures (vdWHs) based on two-dimensional (2D) transition metal dichalcogenides (TMDs) constitute a promising platform for novel electronic and optical devices, such as ultra-thin film solar cells or photodetectors [1], [2].. Single layers of TMDs, such as MoS2, WS2, MoSe2 and WSe2 are direct bandgap semiconductors, which can effectively absorb and emit light at visible and near infrared wavelengths (with photon energies between 1 and 2 eV) [3]. Moreover, 2D TMDs with various bandgaps can be used as building blocks in vertical vdWHs forming novel vdW systems with extraordinary broad absorption across a wide range of the solar spectrum. Pioneer results on vdWHs were demonstrated using physical crystal stacking. However, vertical stacking of 2D TMDs layers in a 3D architecture is not favorable for large-scale applications and direct growth methods must be further investigated. Here, we present a two-step growth process: (1) oxide bilayer films obtained by pulsed laser deposition (PLD) and (2) sulfurized in a tube furnace at high-temperature in a sulfur-rich environment for TMDs heterostructure synthesis. We show that native oxygen vacancies in the PLD-grown precursors serve as niches for sulfur atoms and facilitate MoS2 and WS2 lateral crystal growth. First, we explore how the two-step synthesis process of oxides with variable concentration of oxygen vacancies can be applied for vdWHs growth. Second, these results serve as a potential step to facilitate integration of dissimilar 2D TMDs layers. Lastly, we investigate the use of PLD for the direct growth of quasi-continuous thin films of MoSe2 and WSe2 with two-step grown MoS2 and/or WS2 layers to merge sulfides and selenides in a vdWHs. Thus, our study suggests a way towards fabrication of vdWHs without using individual layer transfer. Potential results of this study are formation of high quality crystals with a good photoluminescence (PL) and strong Raman signals from individual layers. Overlaid, MoS2 and WS2, or MoSe2 and MoS2 form a heterostructure, and display contributions to the Raman spectra from both layers, but significantly quenched PL signal. This may be a promising sign of an effective charge carrier separation within the heterostructure created. The synthesis of heterostructures was examined by XPS, Raman spectroscopy, PL, AFM, SEM, optical microscopy, and TEM. [1] M. K. S. Bin Rafiq et al., Sci. Rep., vol. 10, no. 1, pp. 1–11, 2020. [2] M. Zhong et al., 2D Mater., vol. 5, no. 3, 2018. [3] S. J. Liang, B. Cheng, X. Cui, and F. Miao,Adv. Mater., vol. 32, no. 27, pp. 1–27, 2020

Period	30 May 2022 → 3 Jun 2022
Held at	European Materials Research Society, France
Degree of Recognition	International