The Stanford Photonics Research Center

April 7, 2009

The performance of a solar cell is a sensitive function of the microstructure of the component materials. Recombination of photo-excited carriers at defects is one of the main contributors to low efficiency. For example, in polycrystalline thin films, high angle grain boundaries have been shown to greatly reduce the minority carrier diffusion length. In thin film growth it is common to develop a fiber texture, where a particular crystal plane lies parallel to the film surface. However, there are few options for achieving a biaxial texture, where the crystals are also aligned along a direction in the sample plane. Ion beam assisted deposition (IBAD) is one approach for producing biaxial texture. This talk will present the possibility of using this approach for forming materials for photovoltaic devices. The basic mechanism by which IBAD produces biaxial texture will be presented, including details revealed by recent work on IBAD texturing of MgO, where in-situ reflection high-energy electron diffraction and mass uptake measured during growth have challenged conventional models. The present state of growing Si on IBAD textured seeds will be presented, as well as recent work on directly texturing Si and Ge.