A large thermoelectric power factor in heavily boron-doped p-type nanograined Si with grain sizes ∼30 nm and grain boundary regions of ∼2 nm is reported. The reported power factor is ∼5 times higher than in bulk Si. It originates from the surprising observation that for a specific range of carrier concentrations, the electrical conductivity and Seebeck coefficient increase simultaneously. The two essential ingredients for this observation are nanocrystallinity and extremely high boron doping levels. This experimental finding is interpreted within a theoretical model that considers both electron and phonon transport within the semiclassical Boltzmann approach. It is shown that transport takes place through two phases so that high conductivity is achieved in the grains, and high Seebeck coefficient by the grain boundaries. This together with the drastic reduction in the thermal conductivity due to boundary scattering could lead to a significant increase of the figure of merit ZT. This is one of the rare observations of a simultaneous increase in the electrical conductivity and Seebeck coefficient, resulting in enhanced thermoelectric power factor.

This work analyses the potential of hybrid solar thermoelectric photovoltaic generators (HSTEPVGs) through evaluating their efficiency in converting solar power into electricity for a system consisting of a PV cell placed directly on top of a thermoelectric generator. A theoretical model for terrestrial application which includes the possibility of thermal and optical concentrations is reported. As in the case of pure solar thermoelectric generators, an optimal operation temperature also exists for HSTEPVGs determined by the temperature dependences of both the solar cells and the thermoelectric generators. The study reports an efficiency gain of 4%–5% with respect to the sole PV case, especially in the case of optical concentrations which mitigate the solar cell temperature sensitivity. In addition to these interesting results, the work also reveals the major constrains expected for this approach, along with technological challenges especially regarding the optical properties of the device encapsulation and the solar cell degradation.

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.