In situ cell for grazing-incidence x-ray diffraction on thin films in thermal catalysis.

A cell for synchrotron-based grazing-incidence x-ray diffraction at ambient pressures and moderate temperatures in a controlled gas atmosphere is presented. The cell is suited for the in situ study of thin film samples under catalytically relevant conditions. To some extent, in addition to diffraction, the cell can be simultaneously applied for x-ray reflectometry and fluorescence studies. Different domes enclosing the sample have been studied and selected to ensure minimum contribution to the diffraction patterns. The applicability of the cell is demonstrated using synchrotron radiation by monitoring structural changes of a 3 nm Pd thin film upon interaction with gas-phase hydrogen and during acetylene semihydrogenation at 150 °C. The cell allows investigation of very thin films under catalytically relevant conditions.

Nanowire arrays in multicrystalline silicon thin films on glass: a promising material for research and applications in nanotechnology.

Silicon nanowires (SiNW) were formed on large grained, electron-beam crystallized silicon (Si) thin films of only ∼6 µm thickness on glass using nanosphere lithography (NSL) in combination with reactive ion etching (RIE). Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) studies revealed outstanding structural properties of this nanomaterial. It could be shown that SiNWs with entirely predetermined shapes including lengths, diameters and spacings and straight side walls form independently of their crystalline orientation and arrange in ordered arrays on glass. Furthermore, for the first time grain boundaries could be observed in individual, straightly etched SiNWs. After heat treatment an electronic grade surface quality of the SiNWs could be shown by X-ray photoelectron spectroscopy (XPS). Integrating sphere measurements show that SiNW patterning of the multicrystalline Si (mc-Si) starting thin film on glass substantially increases absorption and reduces reflection, as being desired for an application in thin film photovoltaics (PV). The multicrystalline SiNWs directly mark a starting point for research not only in PV but also in other areas like nanoelectronics, surface functionalization, and nanomechanics.

Smooth anti-reflective three-dimensional textures for liquid phase crystallized silicon thin-film solar cells on glass.

Recently, liquid phase crystallization of thin silicon films has emerged as a candidate for thin-film photovoltaics. On 10 µm thin absorbers, wafer-equivalent morphologies and open-circuit voltages were reached, leading to 13.2% record efficiency. However, short-circuit current densities are still limited, mainly due to optical losses at the glass-silicon interface. While nano-structures at this interface have been shown to efficiently reduce reflection, up to now these textures caused a deterioration of electronic silicon material quality. Therefore, optical gains were mitigated due to recombination losses. Here, the SMooth Anti-Reflective Three-dimensional (SMART) texture is introduced to overcome this trade-off. By smoothing nanoimprinted SiO x nano-pillar arrays with spin-coated TiO x layers, light in-coupling into laser-crystallized silicon solar cells is significantly improved as successfully demonstrated in three-dimensional simulations and in experiment. At the same time, electronic silicon material quality is equivalent to that of planar references, allowing to reach V oc values above 630 mV. Furthermore, the short-circuit current density could be increased from 21.0 mA cm-2 for planar reference cells to 24.5 mA cm-2 on SMART textures, a relative increase of 18%. External quantum efficiency measurements yield an increase for wavelengths up to 700 nm compared to a state-of-the-art solar cell with 11.9% efficiency, corresponding to a j sc, EQE gain of 2.8 mA cm-2.

Silicon Solar Cells on Glass with Power Conversion Efficiency above 13% at Thickness below 15 Micrometer.

Liquid phase crystallized silicon on glass with a thickness of (10-40) µm has the potential to reduce material costs and the environmental impact of crystalline silicon solar cells. Recently, wafer quality open circuit voltages of over 650 mV and remarkable photocurrent densities of over 30 mA/cm2 have been demonstrated on this material, however, a low fill factor was limiting the performance. In this work we present our latest cell progress on 13 µm thin poly-crystalline silicon fabricated by the liquid phase crystallization directly on glass. The contact system uses passivated back-side silicon hetero-junctions, back-side KOH texture for light-trapping and interdigitated ITO/Ag contacts. The fill factors are up to 74% and efficiencies are 13.2% under AM1.5 g for two different doping densities of 1 · 1017/cm3 and 2 · 1016/cm3. The former is limited by bulk and interface recombination, leading to a reduced saturation current density, the latter by series resistance causing a lower fill factor. Both are additionally limited by electrical shading and losses at grain boundaries and dislocations. A small 1 × 0.1 cm2 test structure circumvents limitations of the contact design reaching an efficiency of 15.9% clearly showing the potential of the technology.