We present a stand-alone integrated solar water-splitting device with an active area of 64 cm2 and a long-term stable operation. The modular setup of the device provides a versatile tool to integrate and evaluate various combinations of photoelectrodes and catalysts.
To optimize the optical response of a solar cell, specifically designed materials with appropriate optoelectronic properties are needed. Owing to the unique microstructure of doped nanocrystalline silicon oxide, nc-SiO x :H, this material is able to cover an extensive range of optical and electrical properties. However, applying nc-SiO x :H thin-films in photovoltaic devices necessitates an individual adaptation of the material properties according to the specific functions in the device. In this study, we investigated the detailed microstructure of doped nc-SiO x :H films via atom probe tomography at the sub-nm scale, thereby, for the first time, revealing the three-dimensional distribution of the nc-Si network. Furthermore, n-and p-type nc-SiO x :H layers with various optical and electrical properties were implemented as a window, back contact, and an intermediate reflector layer in silicon heterojunction and multi-junction thin-film solar cells with a focus on the key aspects for adapting the material properties to the specific functions. Here, nc-SiO x :H effectively reduced the parasitic absorption and opened new possibilities for the photon management in the solar cells, thereby, demonstrating the versatility of this material. Remarkably, using our adapted nc-SiO x :H layers in distinct functions enabled us to achieve a combined short circuit current density of 15.1 mA cm -2 for the two a-Si:H sub-cells in an a-Si:H/a-Si:H/µc-Si:H triplejunction thin-film solar cell and an active area efficiency of 21.4 % was realized for a silicon heterojunction solar cell.2
Silicon (Si) has been investigated as a promising photoelectrode material for use in photoelectrochemical water splitting. However, development of Si photocathodes that can operate at a high photocurrent density for solar-driven hydrogen production with long-term stability remains challenging. Herein, we report the fabrication of inverted pyramid textured p-Si photocathodes covered conformally and continuously with a thicknessgradient cobalt phosphide (Co 2 P) layer, which not only effectively isolates p-Si from aqueous electrolyte to avoid corrosion but also efficiently catalyzes the solar-driven hydrogen evolution reaction (HER). Thanks to the unique inverted pyramid structure, the dropcast Co 2 P can distribute all over the p-Si photocathode and form a macroscopically continuous but locally nonuniform layer on the sidewalls of each inverted pyramid. The local nonuniform distribution enables light absorption to be partially separated from catalytic activity. Consequently, the as-fabricated Co 2 P-coated p-Si photocathode exhibits a high photocurrent density of 35.2 mA cm −2 at 0 V versus the reversible hydrogen electrode under AM 1.5G illumination and can photoelectrochemically catalyze the HER above 30 mA cm −2 at least 150 h without notable degradation.
Solar-powered vanadium redox-flow batteries (VRFB) have emerged as an attractive alternative to large-scale and efficient energy storage and conversion. However, due to the stringent charging voltage requirements of vanadium-based systems (1.4-1.7 V), common photobatteries, applying standard photovoltaics with nonoptimized photovoltages, cannot be completely charged bias-free, i.e. by only using bias-free solar energy, or if they can be, only at unpractical low current densities of just a few mA cm −2 . In response to this critical challenge, the present study aimed to design and test a compact device combining a highphotovoltage silicon multijunction solar cell with an all-vanadium continuous-flow battery. In particular, we applied a monolithic triple junction solar cell, which can provide photovoltage of up to 2.2 V. Additionally, we have introduced the concept of increased illumination intensity for the solar VRFB. As a first demonstration, a complete bias-free solar charging at 25 mA cm −2 (300 mW cm −2 illumination) is reported. Moreover, we investigated the influence of the operation parameters of the redox-flow battery itself: the membrane type and the vanadium concentration in the electrolyte (i.e. storage capacity). The presented results provide evidence that the low-cost thin-film silicon based solar VRFB can be considered as an outstanding alternative for practical energy storage and conversion usage. A maximum bias-free solar conversion efficiency of 12.3% was achieved during charging, combined with promising and competitive energy efficiencies for the complete charge-discharge process that can guarantee an overall solar-to-electricity conversion efficiency of >10%.
Although photovoltaic–electrochemical (PV–EC) water splitting is likely to be an important and powerful tool to provide environmentally friendly hydrogen, most developments in this field have been conducted on a laboratory scale so far. In order for the technology to make a sizeable impact on the energy transition, scaled up devices must be developed. Here a scalable (64 cm2 aperture area) artificial PV–EC device composed of triple‐junction thin‐film silicon solar cells in conjunction with an electrodeposited bifunctional nickel iron molybdenum water‐splitting catalyst is shown. The device shows a solar to hydrogen efficiency of up to 4.67% (5.33% active area, H2 production rate of 1.26 μmol H2/s) without bias assistance and wire connection and works for 30 min. The gas separation is enabled by incorporating a membrane in a 3D printed device frame. In addition, a wired small area device is also fabricated in order to show the potential of the concept. The device is operated for 127 h and initially 7.7% solar to hydrogen efficiency with a PV active area of 0.5 cm2 is achieved.
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