Every silicon thin-film solar cell concept is dependent on an excellent optical confinement. As well as texturisation and an anti-reflection coating on the front side, the rear-side needs a reflector for the wavelength region exceeding 600 nm to enhance the long-wavelength response of the solar cell. In our Recrystallised Wafer Equivalent (RexWE) [1] the rear-side of the silicon layer is not accessible during the solar cell process. Therefore, several important features have to be implemented via an intermediate layer: it needs to act as a diffusion barrier of sufficiently high electrical conductivity, an excellent optical reflector, and ideally also as a passivation layer for interface defects. We try to satisfy these requirements with a specially designed reflector. It consists of SiC and SiO2 layers with alternating refractive indices and varying characteristics that can be realised by changing the stoichiometry and layer network. These layer-stacks were implemented into RexWE solar cells by a process sequence including thermal annealing, Si seeding layer deposition, recrystallisation and epitaxial Si growth. To surmount the lack of electrical conductivity of the SiO2 layers we drilled holes through the stacks using a laser. We call this process laser-fired rear access (LFA). The best solar cell incorporating the SiC/SiO2 reflector shows a Jsc of 26.3 mA/cm2 (with front side plasma texture) which constitutes an enhancement of 4 mA/cm2 compared with a single SiC layer. The cell efficiency was thereby increased from 8.8% to 11.1%

We report on the beneficial use of embedded segmented porous silicon broad-band optical reflectors for thin-film epitaxial silicon solar cells. These reflectors are formed by gradual increase of the spatial period between the layer segments, allowing for an enhanced absorption of low energy photons in the epitaxial layer. By combining these reflectors with wellestablished solar cell processing by photolithography, a conversion efficiency of 15Á2% was reached on 73 cm 2 area, highly doped offspec multicrystalline silicon substrates. The corresponding photogenerated current densities (J sc ) were well above 31 mA/cm 2 for an active layer of only 20 mm.

In this work it is studied the influence of different texturizations on minority carrier lifetime of n-type Fz silicon wafers passivated with thin amorphous silicon layers (a-Si:H). For amorphous-crystalline silicon based heterojunction solar cells a good light trapping is essential. Therefore a front side texturization is needed as it can increase the photocurrent due to its low reflectance. The interface between the amorphous emitter and the crystalline base plays an important role for two reasons: firstly, the micromorphic surface topology can generate different deposition regimes that results in different lifetimes, and secondly, the nanomorphic structure also show influences on the lifetime. We compare two different types of wet chemical texturizations by different carbonate solutions and a plasma texturization subsequently covered by a thin layer of a-Si:H by means of plasma-enhanced chemical vapor deposition. The surface morphology produced by the texturization on the silicon wafers is analyzed by scanning electron microscopy and atomic force microscopy. The quality of the passivation of the textured silicon surface by the a-Si:H deposition is evaluated by measuring minority carrier lifetimes with a microwave photo-conductance decay and quasi steady state photo-conductance devices

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In this paper the applicability and efficiency of different intermediate layer (IL) stacks for the implementation in recrystallized wafer equivalent (RexWE) solar cells are investigated. The requirements for the IL in the RexWE concept are short term stability at temperatures above 1400°C, high reflectivity for wavelengths exceeding 600 nm, electrical conductivity and acting as a diffusion barrier against metallic impurities. Various combinations of stoichiometric SiC layers, silicon rich SiC layers and SiO2 layers were tested as IL stacks regarding their performance after a zone melting recrystallization (ZMR) process. For the first time, samples with an IL consisting of a SiC multilayer were recrystallized and successfully processed to solar cells