9We report on the development of high performance triple and quadruple junction solar cells 10 made of amorphous (a-Si:H) and microcrystalline silicon (µc-Si:H) for the application as 11 photocathodes in integrated photovoltaic-electrosynthetic devices for solar water splitting. We 12 show that the electronic properties of the individual sub cells can be adjusted such that the 13 photovoltages of multijunction devices cover a wide range of photovoltages from 2.0 V up to 14 2.8 V with photovoltaic efficiencies of 13.6 % for triple and 13.2 % for quadruple cells. The 15 ability to provide self-contained solar water splitting is demonstrated in a PV-biased 16 electrosynthetic (PV-EC) cell. With the developed triple junction photocathode in the a-17 Si:H/a-Si:H/µc-Si:H configuration we achieved an operation photocurrent density of 7.7 18 mA/cm 2 at 0 V applied bias using a Ag/Pt layer stack as photocathode/electrolyte contact and 19 ruthenium oxide as counter electrode. Assuming a faradic efficiency of 100 %, this 20 corresponds to a solar-to-hydrogen efficiency of 9.5 %. The quadruple junction device 21 provides enough excess voltage to substitute precious metal catalyst, such as Pt by more
Graphical AbstractBias-free solar water splitting is demonstrated using thin film silicon based triple and quadruple junction solar cells with solar-to-hydrogen efficiencies up to 9.5 %.
Photoelectrochemical water splitting promises both sustainable energy generation and energy storage in the form of hydrogen. However, the realization of this vision requires laboratory experiments to be engineered into a large-scale technology. Up to now only few concepts for scalable devices have been proposed or realized. Here we introduce and realize a concept which, by design, is scalable to large areas and is compatible with multiple thin-film photovoltaic technologies. The scalability is achieved by continuous repetition of a base unit created by laser processing. The concept allows for independent optimization of photovoltaic and electrochemical part. We demonstrate a fully integrated, wireless device with stable and bias-free operation for 40 h. Furthermore, the concept is scaled to a device area of 64 cm2 comprising 13 base units exhibiting a solar-to-hydrogen efficiency of 3.9%. The concept and its successful realization may be an important contribution towards the large-scale application of artificial photosynthesis.
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