Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts

Abstract

Affordable, stable and earth-abundant photo-electrochemical materials are indispensable for the large-scale implementation of sunlight-driven hydrogen production. Here we present an intrinsically stable and scalable solar water splitting device that is fully based on earth-abundant materials, with a solar-to-hydrogen conversion efficiency of 14.2%. This unprecedented efficiency is achieved by integrating a module of three interconnected silicon heterojunction solar cells that operates at an appropriate voltage to directly power microstructured Ni electrocatalysts. Nearly identical performance levels were also achieved using a customized state-of-the-art proton exchange membrane (PEM) electrolyzer. The past decade has seen an increase in the urgency to substitute fossil fuels with clean and renewable energy sources. Among all of the renewable sources, solar irradiation is undeniably the most prominent option. The average accessible solar power accounts for over ∼120 000 TW globally; 1 several thousand times the current global energy needs.2 Photovoltaic cells can capture this vast energy resource and convert it into usable electrical energy at high efficiencies. Their implementation in the past years has seen a large growth driven by favorable environmental policies and a steady decrease in their production cost. Although the penetration of photovoltaics has been significant, some challenges for their integration into the electricity grid have started to become evident. Mainly, the intermittent nature of the solar electricity production prevents their large-scale grid implementation without compensation mechanisms that satisfy the demand during low-irradiation periods. Adding energy storage capacity to the grid could directly alleviate the fluctuations on power production. Electrochemical energy storage in batteries is already an interesting option for large-scale stationary energy storage. Electrochemical production of hydrogen from excess solar electricity is also an attractive option for storing solar energy in the form of a fuel which could be used at a later stage for electricity production back into the grid or transportation. 3,4 Furthermore, hydrogen can be stored for prolonged periods of time, so that solar resources are harvested during high irradiation periods and used throughout the year. Because of these multiple advantages, solar-to-fuel approaches have attracted a lot of interest in the renewable energy field and project themselves as a critical technology to achieve large-scale utilization of solar-energy sources. 5-7Despite the strong research interest on solar-hydrogen materials and technologies, there have only been a limited number of demonstrations of solar water splitting devices. Most of these devices show short lifetimes (<1 day), low efficiencies, or use materials and designs that would prevent their practical and economical implementation. 6,8 Deployable solar-hydrogen devices would need to function stably for years, produce robustly and continuously nearly pure H 2 streams, incorporate ...

Designing a hybrid thin‐film/wafer silicon triple photovoltaic junction for solar water splitting

“…To improve the contact at the front surface, a p‐doped nanocrystalline silicon thin layer is placed between the p‐layer and the IOH layer, followed by an H 2 treatment to passivate any dangling bonds. This could potentially lower the energy barrier at the interface between p‐layer and TCO, since nc‐Si:H materials are able to achieve a lower activation energy (51.3 meV) than the p‐SiO x :H material previously used (240.9 meV). The open circuit voltage achieved when including the p‐bilayer at the front is 2.03 V. This strategy also increases the series and shunt resistances, resulting in a similar FF of 0.64 and a PV conversion efficiency of 10.47%.…”

“…Two of the most promising designs are to externally connect several cells in series (D) and to fabricate a monolithic device to produce the necessary voltage and current (B, C). External series connected photovoltaic‐electrochemical device (PV‐EC) devices (D) have the advantage of taking readily available devices to achieve high efficiencies, as shown in literature with three heterojunction cells combined with an earth‐abundant material electrolyser resulting in an efficiency of 14.2%. In addition, it can result in a better current matching, especially at variable spectrum conditions, since all the cells would be of the same technology and would produce similar current densities at a certain spectrum.…”

The Technical and Energetic Challenges of Separating (Photo)Electrochemical Carbon Dioxide Reduction Products

“…Thus, in most cases, multiple photoabsorber configurations, such as tandem photovoltaics coupled to appropriate catalysts, are used to provide the requisite voltage to PEC systems (Rongé et al, 2014). For EC cells, a seriesconnected photovoltaic array could be used to provide the requisite voltage at high efficiency (Jia et al, 2016;Schüttauf et al, 2016).…”

The Influence of Operation Temperature and Variations of the Illumination on the Performance of Integrated Photoelectrochemical Water‐Splitting Devices

“…We investigated PV‐EC devices employing various multi‐junction solar cells under STC and reported on a record solar‐to‐hydrogen (STH) efficiency of 9.5 % using a triple junction cell with the following cell stack: hydrogenated amorphous silicon (a‐Si : H)/hydrogenated amorphous silicon (a‐Si : H)/hydrogenated microcrystalline silicon (μc‐Si : H); together with state‐of‐the‐art metal catalysts . So far, STH efficiencies of over 10 % have been reported for other types of photoelectrodes as well, but these types face stability issues (e. g. perovskite solar cells) or are rather expensive, such as e. g. III−V semiconductors . Therefore, thin film silicon is a promising approach for integrated PV‐EC devices, since silicon is earth abundant, low cost and nontoxic and the technology is upscalable …”