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The concept of third generation photovoltaics is to significantly increase device efficiencies whilst still using thin film processes and abundant non-toxic materials. This can be achieved by circumventing the Shockley-Queisser limit for single band gap devices, using multiple energy threshold approaches. Such an approach can be realised either by incorporating multiple energy levels in tandem or intermediate band devices; or by modifying the incident spectrum on a cell by converting either high energy or low energy photons to photons more suited to the cell band gap; or by using an absorber which is heated by the solar photons with power extracted by a secondary structure. These methods have advantages and disadvantages and are at various stages of realisation. The paper discusses and compares these approaches, with some suggested conclusions for the most appropriate approaches.