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 %.

ABSTRACT:The TiO 2 layer made by electron beam (e-beam) induced evaporation is demonstrated as electron transport layer (ETL) in high efficiency planar junction perovskite solar cells. The temperature of the substrate and the thickness of the TiO 2 layer can be easily controlled with this e-beam induced evaporation method, which enables the usage of different types of substrates. Here, Perovskite solar cells based on CH 3 NH 3 PbI 3-x Cl x achieve power conversion efficiencies of 14.6% on glass and 13.5% on flexible plastic substrates. The relationship between the TiO 2 layer thickness and the perovskite morphology is studied with scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). Our results indicate that pinholes in thin TiO 2 layer lead to pinholes in the perovskite layer. By optimizing the TiO 2 thickness, perovskite layers with substantially increased surface coverage and reduced pinhole areas are fabricated, increasing overall device performance.

factor of 7. This shows that solution-based silicon is a highly promising candidate for industrial-grade applications of solutionbased semiconductors. Evaluation of Precursors NPS and CPSIn literature, most groups reporting silicon fi lms fabricated from a liquid precursor use a cyclic hydridosilane, namely cyclopentasilane (CPS). We decided to use a branched molecule instead, namely neopentasilane (NPS). The molecular structures of CPS and NPS, as well as the process charts for obtaining solid amorphous silicon (a-Si) layers, are shown in Figure 1 . We characterized the NPS used in our process chain by NMR and by mass spectroscopy, showing the expected fi ngerprints mentioned in literature. [ 4 ] Employing NPS over CPS yields major advantages in processing effi ciency as well as in material quality. In general, branched molecules have a considerably better solubility in organic solvents, because the branches act as spacers, preventing strong interactions between the molecules and enabling better intercalation of solvent molecules. [ 5 ] The NPS material is therefore better soluble than CPS, which leads to improved fi lm homogeneity and uniformity. Moreover, in NMR measurements, we found that the NPS-oligomer bears 70% SiH 3 end groups, in contrast to 1.0% for the CPS-oligomer. Such end groups facilitate the cross-linking of the material to a solid network. Since this process is responsible for the formation of silicon-silicon bonds, we expect a positive effect on the coordination of silicon atoms, resulting in less dangling bonds and improved electronic properties. Until now, we have however not been able to demonstrate differences in nanoscopic amorphous silicon structure between CPS and NPS.Another major advantage of employing NPS instead of CPS lies in the differences in material synthesis. The synthesis of the CPS monomer involves a coupling reaction and subsequent chlorination of diphenyldichlorosilane to obtain decachlorocyclopentasilane. This process produces a large amount of various by-products, which are diffi cult to separate and recycle. However, in the synthesis of NPS, we use catalytic rearrangement of octachlorotrisilane to obtain dodecachloroneopentasilane,

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