Wireless photoelectrochemical (PEC) devices promise easy device fabrication as well as reduced losses. Here, the design and fabrication of a stand‐alone ion exchange material‐embedded, Si membrane‐based, photoelectrochemical cell architecture with micron‐sized pores is shown, to overcome the i) pH gradient formation due to long‐distance ion transport, ii) product crossover, and iii) parasitic light absorption by application of a patterned catalyst. The membrane‐embedded PEC cell with micropores utilizes a triple Si junction cell as the light absorber, and Pt and IrOx as electrocatalysts for the hydrogen evolution reactions and oxygen evolution reactions, respectively. The solar‐to‐hydrogen efficiency of 7% at steady‐state operation, as compared to an unpatterned ηPV of 10.8%, is mainly attributed to absorption losses by the incorporation of the micropores and catalyst microdots. The introduction of the Nafion ion exchange material ensures an intrinsically safe PEC cell, by reducing the total gas crossover to <0.1%, while without a cation exchange membrane, a crossover of >6% is observed. Only in a pure electrolyte of 1 m H2SO4, a pH gradient‐free system is observed thus completely avoiding the build‐up of a counteracting potential.

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Solar fuels are a promising way to store solar energy seasonally. This paper proposes an earth‐abundant heterostructure to split water using a photovoltaic‐electrochemical device (PV‐EC). The heterostructure is based on a hybrid architecture of a thin‐film (TF) silicon tandem on top of a c‐Si wafer (W) heterojunction solar cell (a‐Si:H (TF)/nc‐Si:H (TF)/c‐Si(W)) The multijunction approach allows to reach enough photovoltage for water splitting, while maximizing the spectrum utilization. However, this unique approach also poses challenges, including the design of effective tunneling recombination junctions (TRJ) and the light management of the cell. Regarding the TRJs, the solar cell performance is improved by increasing the n‐layer doping of the middle cell. The light management can be improved by using hydrogenated indium oxide (IOH) as transparent conductive oxide (TCO). Finally, other light management techniques such as substrate texturing or absorber bandgap engineering were applied to enhance the current density. A correlation was observed between improvements in light management by conventional surface texturing and a reduced nc‐Si:H absorber material quality. The final cell developed in this work is a flat structure, using a top absorber layer consisting of a high bandgap a‐Si:H. This triple junction cell achieved a PV efficiency of 10.57%, with a fill factor of 0.60, an open‐circuit voltage of 2.03 V and a short‐circuit current density of 8.65 mA/cm2. When this cell was connected to an IrOx/Pt electrolyser, a stable solar‐to‐hydrogen (STH) efficiency of 8.3% was achieved and maintained for 10 hours.

Two of the main problems of society in the near future are the access to clean water and energy. In particular, organic pollutants can be a major health threat. Within available methods, a trade‐off can be established between the pollutant treatment price and the final pollutant concentration that can be achieved. In this paper, a water treatment device is proposed in order to decouple these two variables. It consists of a BiVO4 photoanode combined with a thin film silicon solar cell. BiVO4 is an earth‐abundant material with a bandgap energy of 2.4 eV. Here, its good catalytic properties are shown for the degradation of phenol and chloroform when combined with an external bias voltage of 1 V versus Ag/AgCl. In addition, to cover the voltage needs, an a‐Si:H/nc‐Si:H solar cell has been coupled with the BiVO4 photoanode. This solar cell has been specifically designed to work under the transmitted spectrum of BiVO4, with thicknesses of 300 and 2000 nm for the top and bottom cell, respectively. This device has successfully been fabricated, and tested for removal of organic contaminants from an aqueous solution, performing even better than the BiVO4 photoanode alone with a similar external bias voltage applied.

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