Advanced solar cell concepts1

Material limitations of wafer-based silicon (Si) cell technology and efficiency limitations of thin film solar cell technologies need to be overcome in order to have affordable PV technology. New concepts that strive for better utilization of the sun's spectrum, hence better cell efficiency, are under development. These include multi-junction solar cells, intermediate band solar cells, cells utilizing impurity levels, quantum well and quantum dot solar cells, hot carrier cells and solar cell concepts incorporating spectrum conversion. In multi-junction solar cells, better spectrum utilization is obtained by stacking several solar cells. A record efficiency of over 39% has been achieved under 236 times the sun's light concentration. Analysis of impurity of photovoltaic and intermediate band solar cells has shown that theoretical cell efficiency is about 63.2% for single impurity level and single intermediate band. Energy-shifting of UV photons has been demonstrated by fabricating Si nanocrystals in SiOx and SiNx matrices. Proof of concept has been shown for quantum confinement in Si quantum dots and enhanced photon absorption using metal nanoparticles on the solar cell surface. Similarly, most of the advanced concepts are in the initial stage of experimentation. Significant breakthroughs are required before these concepts can contribute to mainstream PV production.