Photodetectors and Solar Cells Based on Porous Silicon

Over the last few years a great improvement in the efficiency of porous silicon-based solar cells has been achieved. A very important advantage of using porous silicon in photodiodes and solar cells is that the surface roughness of this material can be used to reduce the surface reflectance to very low values (antireflective coatings) and, related to this, the incident radiation is scattered by the nanometric porous structure thus generating diffusive light. Also, the band gap of porous silicon can be adjusted to a more appropriate value than that of bulk silicon. Furthermore, porous silicon-based multilayers, superlattices and graded layers can be readily made, since the refractive index and band gap of porous silicon can be adjusted by varying the formation parameters. It has also to be pointed out that the relatively easy scaling-up of the fabrication process of porous silicon, together with the economy of this process, makes this material very attractive for the industrial development and fabrication of solar cells. In this work, several significant research results on porous silicon photodiodes and solar cells are described, with the purpose of taking advantage of some of the facts mentioned above. In addition, some of the problems inherent to porous materials are described, one of which is the high specific contact resistance.