(545f) From Powder to Large-Area Films - a Solution-Processable Route for Thin Films of Semiconducting 2D Tmds for Solar Energy Conversion

The remarkable semiconducting properties of 2D transition metal dichalcogenides (TMDs) are of great interest to researchers hoping to harness such traits for solar-to-chemical energy conversion (ex., H₂). Nano-TMDs not only provide a new range of thickness tunable optoelectronic properties, but also create a direct path towards ultrathin, flexible devices. However, scalable routes for large-area, high-quality TMD thin films remain a challenge for the commercialization of photoelectrochemical (PEC) devices¹.

We address this issue by developing methods for the solution-based fabrication of nanoflake TMD thin films for incorporation in large area solar energy conversion devices². In this presentation we highlight a novel method for exfoliating commercially available TMD powders via electrochemical pellet intercalation³. Compared to traditional solution-processable methods such as ultrasonication, this method results in nanosheets with superior optoelectronic and photoelectrochemical properties. These specially engineered nanoflakes show higher photocurrent densities (J_ph), lower dark current densities (J_dark), and an absorbed photon-to-current efficiency (APCE) up to 90%. We examine the improved performance by comparing defect types and densities using fluorescent microscopy⁴ and atomic resolution scanning transmission electron microscopy (AR STEM) paired with an integrated differential phase contrast (iDPC) technique⁵.

To process our exfoliated materials into large-area thin films we report the further advancement of our preparation methods toward a continuous roll-to-roll deposition of TMD-based thin films from nanoflake dispersions using a liquid-liquid self-assembly technique⁶. We demonstrate reproducible printing of 100 mm wide TMD flake films on plastic substrates. Thus, we outline a pathway for fully solution-processable 2D-TMD devices beginning with as-received bulk TMD powder and finishing with large-area nano-flake thin films.

References

(1) Yu, X.; Sivula, K. Toward Large-Area Solar Energy Conversion with Semiconducting 2D Transition Metal Dichalcogenides. ACS Energy Lett. 2016, 1 (1), 315–322. https://doi.org/10.1021/acsenergylett.6b00114.

(2) Wells, R. A.; Sivula, K. Assembling a Photoactive 2D Puzzle: From Bulk Powder to Large-Area Films of Semiconducting Transition-Metal Dichalcogenide Nanosheets. Acc. Mater. Res. 2023, 4 (4), 348–358. https://doi.org/10.1021/accountsmr.2c00209.

(3) Wells, R. A.; Zhang, M.; Chen, T.-H.; Boureau, V.; Caretti, M.; Liu, Y.; Yum, J.-H.; Johnson, H.; Kinge, S.; Radenovic, A.; Sivula, K. High Performance Semiconducting Nanosheets via a Scalable Powder-Based Electrochemical Exfoliation Technique. ACS Nano 2022, 16 (4), 5719–5730. https://doi.org/10.1021/acsnano.1c10739.

(4) Zhang, M.; Lihter, M.; Chen, T.-H.; Macha, M.; Rayabharam, A.; Banjac, K.; Zhao, Y.; Wang, Z.; Zhang, J.; Comtet, J.; Aluru, N. R.; Lingenfelder, M.; Kis, A.; Radenovic, A. Super-Resolved Optical Mapping of Reactive Sulfur-Vacancies in Two-Dimensional Transition Metal Dichalcogenides. ACS Nano 2021, 15 (4), 7168–7178. https://doi.org/10.1021/acsnano.1c00373.

(5) Yücelen, E.; Lazić, I.; Bosch, E. G. T. Phase Contrast Scanning Transmission Electron Microscopy Imaging of Light and Heavy Atoms at the Limit of Contrast and Resolution. Sci Rep 2018, 8 (1), 2676. https://doi.org/10.1038/s41598-018-20377-2.

(6) Wells, R. A.; Johnson, H.; Lhermitte, C. R.; Kinge, S.; Sivula, K. Roll-to-Roll Deposition of Semiconducting 2D Nanoflake Films of Transition Metal Dichalcogenides for Optoelectronic Applications. ACS Appl. Nano Mater. 2019, 2 (12), 7705–7712. https://doi.org/10.1021/acsanm.9b01774.