Lifetime measurements of crystalline silicon thin films by microwave photo conductance decay

The development of crystalline silicon thin films (cSiTF) for several solar cell concepts is pursued by various research groups. A common challenge is the electrical characterisation of silicon films with a thickness in the range of 2 to 20 μm. Since the improvement of layer quality and the optimisation of layer thickness is a critical factor, the measurement of the diffusion length respectively the minority carrier lifetime of such silicon films is a very important factor and will therefore be addressed in this paper. The solar cell structure including substrate and possibly dielectric intermediate layers is one of the major challenges for these lifetime measurements. Besides that the lifetime regime below 5 μs is another challenge for certain measurement techniques. Therefore a system for microwave photo conductance decay (MWPCD) measurements by Semilab was used in these experiments and a modified analysis algorithm was implemented. Finally, the lifetime measurements of cSiTF fabricated by epitaxial growth and by recrystallisation will be presented.