Photocatalytic response in the shade

Supply-driven photoelectrochemical (PEC) water splitting is an attractive way to convert solar energy into chemical energy. Among many photoelectrode materials, crystalline silicon (c-Si) has attracted much attention due to its abundance, narrow bandgap, and band edge positioning suitable for hydrogen evaporation (HER). However, c-Si suffers from low photovoltage generated from the solid-liquid junction.

Various strategies, such as pn homojunctions construction, metal-insulator-semiconductor (MIS) terminals and pn heterojunctions, have been adopted to obtain high photovoltage. MIS junctions have been the center of attention in PEC water slots due to their simple manufacturing and the ability to achieve higher efficiency than pn junctions. However, very few Si-based MIS photocathodes have been reported with efficiencies higher than 5%, much lower than those of pn-knot photocathode (10%).

One of the main challenges of p-Si MIS photocathodes for higher efficiency is the absorption of parasitic light from HER catalysts such as Pt, Ni-Mo, and so on. Traditional MIS photocathodes are made from p-Si, where the photogenerated microcontrollers (electrons) drive the reduced reactivity at the front surface. This could translate to the need to place the catalyst at the same side of the MIS knot. Thus, the parasitic light scattering from catalysts severely limits the photocurrent density. The metal layers in a MIS junction also cause optical loss. Another limiting feature is the lack of low-action metals to form a large band balanced by p-Si in a MIS junction, leading to low photovoltage.

In a research article published in National Science Review, scientists at Tianjin University are exhibiting a highly scalable MIS photocathode designed from n-Si, which overcomes the challenges that severely hamper the development of the p-Si MIS photocathode.

Unlike previous jobs that employ micro-carriers to manage the surface reduction, most carriers (electrons) of n-Si MIS photocathode are used in this work. On this simple, non-controversial yet effective modification, the MIS knot and catapult can be placed on either side of n-Si, which avoids the catalpa light protection problem.

In addition, this MIS photocathode constructed from n-Si handles the withdrawal of metallic materials with appropriate work function to generate large band resistance for p-Si MIS photocathode. By using high-transmittance indium tin oxide (ITO) as the high-action metallic material for n-Si MIS photocathode, the trade-off value between metal coating and light capture in the face of high-activity metals is increased. from further.

As a result, this n-Si MIS photocathode-responsive illumination exhibits a light absence of more than 90%, photovoltage up to 570 mV, and a recorded efficiency of 10.3%, exceeding on traditional MIS p-Si photocathodes.

This front-end strategy demonstrates the potential to promote rational design of solar-powered photoelectrochemical systems that use catalysts with poor light transmission, a step towards a major commercialization of solar water separation at the time. future.

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This research is supported by China National R&D Program, China National Institute of Natural Science, Tianjin City Natural Science Foundation, and the Induction Talents Program for Universities.

View the article:

Shujie Wang, Tuo Wang, Bin Liu, Huimin Li, Shijia Feng and Jinlong Gong

Spatial separation of light-absorbing and repulsive sites in n-Si photocathodes for solar water scattering

Natl Sci Urr 2020; doi: 10.1093 / nsr / nwaa293

https: //doi.org /10.1093 /nsr /nwaa293