We report on the development of tandem, triple, and quadruple junction thin film silicon based photocathodes for solar water splitting. Combining thin films of amorphous hydrogenated silicon (a-Si:H) and microcrystalline silicon (µc-Si:H) in multijunction solar cells allows for both: (i) an efficient utilization of the solar spectrum, thus for the generation of high photocurrents and (ii) for an extended photovoltage range. We show that the electronic properties of the individual series-connected sub cells can be adjusted to cover a wide range of photovoltages from 1.5 V up to 2.8 V with electrical conversion efficiencies up to 13.5 %. The ability to tune the photovoltage without impairing the device efficiency represents an outstanding property of thin film silicon solar cells and is crucial to meet the overpotential requirements of various photoelectrolysis systems.a-Si:H and µc-Si:H layers were deposited by plasma enhanced chemical vapor deposition, using a mixture of SiH₄, H₂, CH₄, CO₂, B(CH₃)₃ and PH₃ gases. Solar cells were investigated by current density-voltage measurements under AM 1.5 illumination and quantum efficiency measurements. The applicability of the multijunction solar cells as photocathodes in photoelectrochemical (PEC) water splitting devices was subsequently investigated based on 3- and 2-electrode electrochemical measurements.The multijunction solar cells were optimized in terms of photovoltage and photocurrent by integrating thin films of microcrystalline silicon oxide (µc-SiOx) as intermediate reflecting layers as well as by adjusting the thicknesses of the individual sub cells (photocurrent-matching). The latter is needed to equally distribute the total photocurrent to the individual sub cells and hence, to avoid current limitation by one of the sub cells. We developed a-Si:H/a-Si:H tandem junction, a-Si:H/µc-Si:H/µc-Si:H and a-Si:H/a-Si:H/µc-Si:H triple junction, and a-Si:H/a-Si:H/µc-Si:H/µc-Si:H quadruple junction solar cells, which provide open-circuit voltages Voc up to 1.9 V, 2.3 V, and 2.8 V, respectively. The photocurrent matching is evaluated by means of quantum efficiency measurements.The performance of the developed silicon based photocathodes, with respect to photocurrent densities and onset potentials for cathodic current were evaluated in an integrated PEC device configuration. Furthermore, we demonstrate the ability to provide self-contained solar water splitting in a 2-electrode configuration without any external bias potential. Hereby, we show that our high voltage photocathodes provide enough excess-voltage to substitute precious metal catalysts, like platinum, by more abundant materials, like nickel, without impairing the solar-to-hydrogen efficiency of the PEC device.