Challenges and Perspectives in Tandem Thermoelectric–Photovoltaic Solar Energy Conversion

This paper discusses enhancements of solar energy conversion by photovoltaic (PV) cells using thermoelectric (TE) generators harvesting the heat released by the PV cell. To optimize the TE-PV coupling, PV efficiency losses are analyzed by decoupling source- and absorber-dependent losses. This shows that the implementation of a tandem PV-TE device leads to a substantial increase of available power densities depending on the PV material. We further show that a major increase of the conversion efficiency can be achieved by adding an intermediate layer between the PV and the TE stage capable of absorbing the under-the-gap fraction of the solar spectrum. This increase of efficiency is discussed and commented upon also in view of the constraints PV-TE coupling imposes to the TE generator layout and to its material characteristics. The critical importance of effective heat dissipation will also be addressed. The conclusion is reached that not only could tandem PV-TE cells improve the conversion rate of existing solar cells but also that they could enable the use of lower cost PV materials, currently not considered because of their marginal PV efficiency.