For substrate n-i-p-type cells rough reflecting back contacts are used in order to enhance the short-circuit currents. The roughness at the electrode∕silicon interfaces is considered to be the key to efficient light trapping. Root-mean-square (rms) roughness, angular resolved scattering intensity, and haze are normally used to indicate the amount of scattering, but they do not quantitatively correlate with the current enhancement. It is proposed that the lateral dimensions should also be taken into account. Based on fundamental considerations, we have analyzed by atomic force microscopy specific lateral dimensions that are considered to have a high scattering efficiency. Textured back reflectors with widely varying morphologies have been developed by the use of sputtered Ag and Ag:AlOx layers. For these layers we have weighted the rms roughness of the surface with the lateral dimensions of the effective scattering features. A clear correlation is found between the current generation under (infra)red light in microcrystalline (μc-Si:H) n-i-p solar cells and the weighted rms value of the Ag back contacts. Furthermore, the surface plasmon absorption of the rough Ag back contact has been found to be a significant limiting factor for the current enhancement. Using Ag:AlOx layers on glass, deposited at substrate temperatures below 300°C, a μc-Si:H n-i-p solar cell is obtained with an efficiency of 8.1%. Using textured Ag layers made at a higher substrate temperature on a stainless steel substrate we have developed a hot-wire chemical vapor deposited μc-Si:H n-i-p-type solar cell with 8.5% efficiency.

Close‐packed and non‐close‐packed colloidal photonic crystals of silica spheres have been imaged in real space to reveal their 3D structure. Although the lattice spacings are of the order of a micrometer, these crystals can also be characterized in reciprocal space using small‐angle X‐ray scattering (see figure). After infiltration with silicon (see inset), the internal 3D structure of these photonic crystals can only be probed using X‐ray scattering.

Hot Wire Chemical Vapor Deposition (HWCVD) is shown to be a fast method for the deposition of protocrystalline silicon films from undiluted silane. Intrinsic silicon-hydrogen films (2 µm thick) have been deposited by HWCVD on plain stainless steel as well as on stainless steel precoated with a n-type doped microcrystalline silicon layer. In X-ray diffraction experiments, the linewidths of the first sharp peak (FSP) were 5.59 ± 0.09 degrees and 5.29 ± 0.11 degrees, respectively, indicating improved medium-range order and a template effect due to the µc-Si:H n-layer. For thinner layers (0.7 µm thick), the linewidths of the FSP were 5.29 ± 0.09 degrees and 5.10 ± 0.09 degrees. These FSPs are as narrow as for optimized i -layers made by H 2 -diluted plasma deposition, however, at a much higher deposition rate (1 nm/s), at moderate temperature (250 °C), and without the use of H 2 dilution. In accompanying transmission electron micrographs, the layers show a significant concentration of elongated small voids in the growth direction that are not interconnected. Small Angle X-ray Scattering (SAXS) results are consistent with these observations. We suspect that the void nature allows the bulk of the film to be more ordered. The utilization of such layers in n-i-p solar cells on plain stainless steel leads to cells with a remarkably good stability, showing a decrease of the fill factor of less than 10 % during 1500 h of light soaking.

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