Wafer-Scale Ultrathin, Single-Crystal Si and GaAs Photocathodes for Photoelectrochemical Hydrogen Production

Abstract

Crystalline Si and III-V compound semiconductors with appropriate band edge positions for the reduction of water have been widely utilized in photoelectrochemical (PEC) cells for the hydrogen evolution reaction (HER). However, the high cost of manufacturing those PEC cell photoabsorbers makes it difficult to achieve cost-effective hydrogen production. To overcome this issue, a new approach to fabricate a photoabsorber with low cost yet high performance for the HER is highly necessary. Here, we present a controlled fracture method, the so-called spalling process, to fabricate a cost-effective thin semiconductor applicable to the PEC HER. Using this method, a wafer-scale thin Si, whose thickness can be controlled from a few micrometers to sub-50 μm, was fabricated from a thick Si mother substrate without material loss. Pt nanoparticle-decorated 16 μm thick spalled Si with an np rear junction exhibited an HER onset potential of 332 mV (vs reversible hydrogen electrode (RHE)) and a photocurrent density of 20.1 mA cm at 0 V (vs RHE), which are the best performances among previously reported planar-type thin Si-based photocathodes. Finally, we demonstrated that 20 μm thick GaAs could also be successfully fabricated by the spalling process, while exhibiting a PEC HER performance comparable to 350 μm thick bulk GaAs.

Thin silicon via crack-assisted layer exfoliation for photoelectrochemical water splitting

“…Texturing leads to an improvement in current density by 4.6 mA/cm 2 due to enhanced light trapping compared to the planar photoanode even $20 mm of material is removed during the texturing process (see Figure S5). In addition, E onset decreases from 1.56 to 1.39 V, showing enhanced photovoltage (V ph ) from the removal of defects on the fracture surface during the surface texturing process (Lee et al, 2018b). This confirms that the surface texturing is crucial to achieve high performance in Si film photoanodes.…”

“…One of the promising ways for realizing low-cost PEC-based water splitting with high performance is through utilization of thin (<50 mm) Si for the design of photoelectrodes, thereby reducing the volume of c-Si material by an order of magnitude and promoting enhanced carrier collection (Jung et al, 2015;Lee et al, 2018b;Liu et al, 2020;Massiot et al, 2020;Zhang et al, 2017). In addition to cost reduction, the use of thin Si films offers additional advantages: (1) The performance of the solar energy conversion devices becomes less affected by the material quality (e.g., bulk minority carrier lifetime) (Jeong et al, 2013), (2) enhanced photovoltage can be realized due to photo-generated carrier concentration effect from reduced Si thickness (Brendel and Queisser, 1993;Zhang et al, 2014), (3) the total weight of the device can be lowered, and (4) the high flexibility and impact resistance enables integration on irregular surfaces such as electric vehicles, ships, aeroplanes, and drones (see Figure 1A).…”

Semiconductor Thin Film Based Metasurfaces and Metamaterials for Photovoltaic and Photoelectrochemical Water Splitting Applications

“…The Spalling process has also been demonstrated as an efficient way to make metal backed single crystalline ultrathin semiconductor layers. The use of Si and GaAs, as single crystalline semiconductor layers, in this configuration could offer a high efficiency photocathode …”

Strong Interference in Planar, Multilayer Perfect Absorbers: Achieving High-Operational Performances in Visible and Near-Infrared Regimes

“…The spalling process is another synthesis approach that creates metal-backed, single-crystalline, ultrathin semiconductor layers. Using Si as single-crystalline, high-mobility semiconductors in MS configurations offers a high-efficiency photocathode [90]. In addition to semiconductor-based WS cells, utilizing hot, electron-based designs has garnered much attention for obtaining highly stable, metal-based photoanodes [91].…”