In view of the combinatorial approach to discovery of new thermoelectric materials,
it is highly desirable to have fast measurement techniques, if possible with capabilities to
access local fluctuations or gradients in material properties.
Using the generalized Planck& #39;s law of radiation  for fitting the photoluminescence
spectra is the most appropriate technique to access the quasi Fermi level splitting and the
temperature of the carriers in a semiconductor. These two parameters enable to determine
Seebeck coefficients for the material as a new photo-Seebeck effect .
The absolutely calibrated photoluminescence intensity profile with the spatial
coordinates combined with Callen coupled transport equations and with the kinetic
expression of the transport parameters under the relaxation time approximation enable us
to determine: the Seebeck coefficient, the electrical conductivity, the thermal electron and
hole conductivity, the mobilities, the diffusion coefficients and the heat transferred from the
carriers to the lattice. All these parameters can be obtained either for electrons or for
holes, even simultaneously, for intrinsic semiconductor in ambipolar regime.
The method has been applied to a multi-quantum well structure of InGaAsP. Since
the luminescence comes from the wells, this method enables to access the transport
properties in the plane of the wells inside the whole structure. Since photoluminescence
does not require p-n junction nor high electrical conductivities for the measurement, this
optical contactless measurement technique of thermoelectrinc transport parameters
involving quasi-equilibrium carriers enables to access properties inside a given layer of the
whole structure or in materials with very low conductivities.
We will also show the perspectives offered for the research of new thermoelectric materials.
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 Gibelli et al., Phys. Rev. Appl., 5 (2) 2016
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 Delamarre, Appl. Phys. Lett., 2012
 Gibelli et al., Physica B, October 2016
Double resonant tunneling barriers are considered for an application as energy selective contacts in hot carrier solar cells. Experimental symmetric and asymmetric double resonant tunneling barriers are realized by molecular beam epitaxy and characterized by temperature dependent current-voltage measurements. The negative differential resistance signal is enhanced for asymmetric heterostructures, and remains unchanged between low- and room-temperatures. Within Tsu-Esaki description of the tunnel current, this observation can be explained by the voltage dependence of the tunnel transmission amplitude, which presents a resonance under finite bias for asymmetric structures. This effect is notably discussed with respect to series resistance. Different parameters related to the electronic transmission of the structure and the influence of these parameters on the current voltage characteristic are investigated, bringing insights on critical processes to optimize in double resonant tunneling barriers applied to hot carrier solar cells.
We report on the opto-electrical characterization of quantum-well solar cells designed for generation of hot carriers. Short-circuit current is proportional to laser power in the entire range. Population density, temperature and quasi-Fermi level splitting of photo-generated confined carriers are investigated by fitting the full luminescence spectra using generalized Planck’s law. The energy-dependent absorptivity is identified to obtain good fit accuracy and takes into account the absorption of excitons and free carriers in the quantum well. Furthermore, electrical injection and extraction across the barriers modify the temperature of the quantum well carrier population linearly, hinting at the role of barriers as semi-selective high-energy contact.
The hot carrier solar cell is a very promising clean energy technology, with the potential to achieve high conversion yields with constrained costs. Due to the hot carrier effect, the estimation of the achievable voltage needs some theoretical developments. The classical approach is to consider isentropic energy selective contacts, converting the excess of kinetic energy of the hot carriers into electrical potential energy. Here we show the differences between the ideal case of isentropic contacts and the more realistic one, with an output voltage of the cell depending on the transmission function. We particularly emphasize the importance of the transmission function of the contact on both output current and output voltage, modifying thereby the classical view of the output power dependence on the transmission function.