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,

We report on a liquid hydridosilane precursor ink prepared via the ultrasonically induced ring-opening polymerisation of cyclopentasilane (SiH) without irradiation by ultraviolet light. The sonication is carried out in N atmosphere at temperatures between 20 and 75°C. We use size exclusion chromatography (SEC) to show polymer growth and estimate molecular mass with increasing sonication time. In combination with UV-vis transmission measurements, further SEC analysis is used to compare solutions subjected to either purely thermal or ultrasonic treatment at the same process temperature and for the same duration. Our findings provide strong evidence showing that the initiation of the polymerisation is sonocatalytic in nature and not thermic due to the macroscopic temperature of the solution. The liquid precursor is used to produce homogeneous hydrogenated amorphous silicon (a-Si:H) thin films via spin coating and pyrolytic conversion. The optoelectronic properties of the films are subsequently improved by hydrogen radical treatment. Fourier transform infrared spectroscopy (FTIR) is used to determine a compact film morphology and electrical conductivity measurements show that the layers attain a light-to-dark photosensitivity ratio of 2×10 making them suitable for application in optoelectronic devices.

The preparation of a printable silicon ink using semiconductor grade and commercially available trisilane (Si3H8) is reported. The synthesis is carried out in solution at room temperature or below in N2 atmosphere at ambient pressure and involves an initial sonication step, followed by irradiation with ultraviolet light. The production of higher order silanes via ultrasound is demonstrated using gas chromatography and nuclear magnetic resonance measurements are used to show that a combined sonophotolytic treatment yields a highly branched silicon hydride polymer. In addition, scanning electron microscopy (SEM) images are used to ascertain the sonocatalytic production of silicon nanoparticles. Furthermore, it is argued that these particles are partially responsible for enabling dramatically accelerated polymer growth, not otherwise observed in the same amount of time using ultraviolet light alone. Finally, the utility of the ink used in this study is demonstrated for the field of printable electronics by fabricating amorphous silicon thin films by spin‐coating and atmospheric pressure chemical vapor deposition with optoelectronic properties approaching those of state‐of‐the‐art plasma enhanced chemical vapor deposition (PECVD) material.

The article demonstrates the fabrication of a-Si:H thin films in a N 2 -filled glove box via atmospheric pressure chemical vapor deposition (APCVD) using a vaporized silicon hydride polymer/silicon nanoparticle composite ink prepared from trisilane (Si 3 H 8 ). It is shown via Raman spectroscopy that the films exhibit good short and mid-range atomic order. Fourier transform infrared spectroscopy reveals a fairly compact microstructure and a hydrogen concentration of 13-18 at.%. Photothermal deflection spectroscopy demonstrates a sub band gap absorption only a factor of $6 higher than that of solar-grade plasma-enhanced CVD (PECVD) material. As a demonstration of the utility of our ink, c-Si wafer surface passivation layers are deposited resulting in effective minority charge carrier lifetimes exceeding 400 ms. These lifetimes constitute the as of yet highest reported values achieved using liquid precursors for bifacial coating without subsequent hydrogen radical treatment. The high electronic quality of the layers is shown via the fabrication of a n-i-p thin-film solar cell with an APCVD intrinsic absorber layer exhibiting an efficiency of 3.4% and hence, placing its photovoltaic performance among the highest reported for cells processed from the liquid phase and without a back reflector.

Hematite (α-Fe 2 O 3) is known for poor electronic transport properties, which are the main drawback of this material for optoelectronic applications. In this study, we investigate the concept of enhancing electrical conductivity by the introduction of oxygen vacancies during temperature treatment under low oxygen partial pressure. We demonstrate the possibility of tuning the conductivity continuously by more than five orders of magnitude during stepwise annealing in a moderate temperature range between 300 and 620 K. With thermoelectric power measurements, we are able to attribute the improvement of the electrical conductivity to an enhanced charge-carrier density by more than three orders of magnitude. We compare the oxygen vacancy doping of hematite thin films with hematite nanoparticle layers. Thereby we show that the dominant potential barrier that limits charge transport is either due to grain boundaries in hematite thin films or due to potential barriers that occur at the contact area between the nanoparticles, rather than the potential barrier within the small polaron hopping model, which is usually applied for hematite. Furthermore, we discuss the transition from oxygen-deficient hematite α-Fe 2 O 3−x towards the magnetite Fe 3 O 4 phase of iron oxide at high density of vacancies.

No abstract

Raman spectra of microcrystalline silicon layers have been recorded in‐situ during growth. The spectra have been collected under realistic conditions for solar cell deposition. To enable these measurements an electrode with an optical feed through has been developed. By using a metallic grid to shield the feed through it is possible to achieve homogeneous deposition of µc‐Si:H at a sufficient optical transmission. In‐situ Raman measurements were carried out during the deposition of a layer with an intentionally introduced gradient in crystallinity that was seen in‐situ as well in reference measurements performed on the same layer ex‐situ. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Parameters for the structural short (SRO) and medium range order (MRO) of hydrogenated amorphous silicon (a-Si:H) films on the edge of the microcrystalline silicon (mc-Si:H) phase transition were studied with Raman spectroscopy. The observed samples were deposited using radio frequency plasma enhanced chemical vapor deposition. The studied films were grown with various constant and non-constant silane concentrations (SCs).A substrate dependent correlation of SC to the intensity ratio (I MRO ) of the transversal acoustical (TA) and the transversal optical (TO) phonon bands was found. A strong correlation between width and position of the (TO) phonon band was observed. These two easily accessible parameters show an increase of SRO when I MRO decreases.