We present a silicon nitride/polymer hybrid multilayer moisture barrier for flexible electronics made entirely by hot wire chemical vapor deposition (HWCVD) at substrate temperatures below 100 °C. Using the initiated CVD (iCVD) variant of HWCVD for the polymer layers, these can be extremely thin, while efficiently decoupling the defects in consecutive inorganic layers. Although a single layer of low temperature SiNx is more prone to have pinholes than its state‐of‐the‐art high temperature equivalent, we have achieved a simple three‐layer structure consisting of two low‐temperature SiNx layers with a polymer layer in between, which is pinhole free and shows a water vapor transmission rate (WVTR) as low as 5 × 10–6 g/m2/day at a temperature of 60 °C and a relative humidity of 90%. This WVTR is low enough for organic devices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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We have implemented a number of methods to improve the performance of proto-Si/proto-SiGe/µc-Si:H triple junction n-i-p solar cells in which the top and bottom cell i-layers are deposited by Hot-Wire CVD. Firstly, a significant current enhancement is obtained by using textured Ag/ZnO back contacts developed in house instead of plain stainless steel. We studied the correlation between the integrated current density in the long wavelength range (650-1000 nm) with the back reflector surface roughness and clarified that the rms roughness from 2D AFM images correlates well with the long wavelength response of the cell when weighted with a Power Spectral Density function. For single junction 2-µm thick µ c-Si:H n-i-p cells we improved the short circuit current density from the value of 15.2 mA/cm 2 for plain stainless steel to 23.4 mA/cm 2 for stainless steel coated with a textured Ag/ZnO back reflector. Secondly, we optimized the µ c-Si:H n-type doped layer on this rough back reflector, the n/i interface, and in addition we used a profiling scheme for the H 2 /SiH 4 ratio during i-layer deposition. The H 2 dilution during growth was stepwise increased in order to prevent a transition to amorphous growth. The efficiency that was reached for a single junction µ c-Si:H n-i-p cell was 8.5%, which is the highest reported value for hot-wire deposited cells of this kind, whereas the deposition rate of 2.1 ≈/s is about twice as high as in record cells of this type so far. Moreover, these cells are shown to be totally stable under light-soaking tests. Combining the above techniques, a rather thin triple junction cell (total silicon thickness 2.5 µ m) has been obtained with an efficiency of 10.9%. Preliminary light-soaking tests show that these triple cells degrade by less than 4%.

The deposition process of silicon nitride (SiNx) by hot-wire chemical vapor deposition (HW CVD) is investigated by exploring the effects of process pressure and gas-flow ratio on the composition of the deposited SiNx films. Furthermore, experiments with D2 and deuterated silane were performed to gain further insight in the deposition reactions taking place. It appeared that the N/Si ratio in the layers determines the structural properties of the deposited films and since the volume concentration of Si-atoms in the deposited films is constant with N/Si ratio, the structure of the films are largely determined by the quantity of incorporated nitrogen. Because the decomposition rate of the ammonia source gas is much smaller than that of silane, the properties of the SiNx layers are largely determined by the ability to decompose the ammonia and to incorporate nitrogen into the growing material. It appeared that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high value of 7 nm/s for dense transparent SiNx films, much faster than conventional deposition techniques for SiNx can offer. Despite this high deposition rate good control over the composition is achieved by varying the flow ratio of the source gasses. Depositions performed with deuterated silane as a source gas reveal that almost all hydrogen in N-rich films originates from ammonia, probably caused by SiNx matrix formation by cross linking reactions

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