Balancing Light Absorption and Charge Transport in Vertical SnS2 Nanoflake Photoanodes with Stepped Layers and Large Intrinsic Mobility

Significant optical absorption in the blue-green spectral range, high intralayer carrier mobility, and band alignment suitable for water splitting suggest tin disulfide (SnS2) as a candidate material for photo-electrochemical applications. In this work, vertically aligned SnS2 nanoflakes are synthesized directly on transparent conductive substrates using a scalable close space sublimation (CSS) method. Detailed characterization by time-resolved terahertz and time-resolved photoluminescence spectroscopies reveals a high intrinsic carrier mobility of 330 cm(2) V-1 s(-1) and photoexcited carrier lifetimes of 1.3 ns in these nanoflakes, resulting in a long vertical diffusion length of approximate to 1 mu m. The highest photo-electrochemical performance is achieved by growing SnS2 nanoflakes with heights that are between this diffusion length and the optical absorption depth of approximate to 2 mu m, which balances the competing requirements of charge transport and light absorption. Moreover, the unique stepped morphology of these CSS-grown nanoflakes improves photocurrent by exposing multiple edge sites in every nanoflake. The optimized vertical SnS2 nanoflake photoanodes produce record photocurrents of 4.5 mA cm(-2) for oxidation of a sulfite hole scavenger and 2.6 mA cm(-2) for water oxidation without any hole scavenger, both at 1.23 V-RHE in neutral electrolyte under simulated AM1.5G sunlight, and stable photocurrents for iodide oxidation in acidic electrolyte.