Mixed-Phase (2H and 1T) MoS2 Catalyst for a Highly Efficient and Stable Si Photocathode

Abstract

We describe the direct formation of mixed-phase (1T and 2H) MoS2 layers on Si as a photocathode via atomic layer deposition (ALD) for application in the photoelectrochemical (PEC) reduction of water to hydrogen. Without typical series-metal interfaces between Si and MoS2, our p-Si/SiOx/MoS2 photocathode showed efficient and stable operation in hydrogen evolution reactions (HERs). The resulting performance could be explained by spatially genuine device architectures in three dimensions (i.e., laterally homo and vertically heterojunction structures). The ALD-grown MoS2 overlayer with the mixed-phase 1T and 2H homojunction passivates light absorber and surface states and functions as a monolithic structure for effective charge transport within MoS2. It is also beneficial in the operation of p-i-n heterojunctions with inhomogeneous barrier heights due to the presence of mixed-phase cocatalysts. The effective barrier heights reached up to 0.8 eV with optimized MoS2 thicknesses, leading to a 670 mV photovoltage enhancement without employing buried Si p-n junctions. The fast-transient behaviors via light illumination show that the mixed-phase layered chalcogenides can serve as efficient cocatalysts by depinning the Fermi levels at the interfaces. A long-term operation of ~70 h was also demonstrated in a 0.5 M H2SO4 solution.

Doping‐Assisted Phase Changing Effect on MoS2 Towards Hydrogen Evolution Reaction in Acidic and Alkaline pH

“…Deconvoluted S 2p XPS are summarized in Table S3 of supporting information. Deconvoluted XPS spectrum of Mo and S for NMS2 and NMS3 confirmed the presence of both 1T and 2H phases . The Mo 3p XPS profile of MoS 2 and NMSd are shown in Figure (a–d).…”

Metal Chalcogenides on Silicon Photocathodes for Efficient Water Splitting: A Mini Overview

“…It was also stable during 10,000 s during PEC operation [81]. Joe et al, found that the mixed-phase MoS 2 could improve the Si photocathode for PEC WS by regulating the systems impedance [53].…”

“…Note also that there exists Fermi-level depinning (FLDP ox ) by the presence of oxide interfaces, e.g., SiO x between the metal and Si [129]. We also suspect that the presence of the continuously mixed phases would lead to ideal band edge pinning, indicative of facilitated charge transfer in the catalyst layer [53], reducing R cat . Moreover, the catalysts with a lateral dimension less than the depletion width and with different work function values form inhomogeneous junctions to the absorber.…”

“…Ho et al successfully grew a mixed-phase and continuous 1T and 2H homojunction MoS2 catalyst film on Si, via ALD at low temperature (250 °C) [76]. The conduction band energy relative to vacuum level of 2H phase of MoS2 and the work function of 1T phase are similar (~4.2 eV) [79] which secures band alignment, and in view of this, Joe et al explained that mixed-phase MoS2/silicon junction photocathode showed effective photocatalytic performance through the efficient charge transfer within the MoS2 homojunction heterophase [53]. The ALDgrown MoS2 layer functions as a monolithic structure for effective charge transport within the film and was shown that the effective barrier height reached up to 0.8 eV with the optimized MoS2 thickness.…”

“…Therefore, it is important to understand how the deposited TM(D)C material (here, MoS 2 ) on Si surface affects the charge recombination. In the literature [53,74,81], it was argued that depending on the thickness of the MoS 2 catalyst layer, the Fermi-level pinning (FLP ss ) tends to be gradually relieved, possibly resulting in suppression of the R surf . The reduced R surf leads to increasing the V ph , results in reducing the R scr and the R quasi .…”