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Reversible electron–hole separation in a hot carrier solar cell

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Reversible electron–hole separation in a hot carrier solar cell
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Hot-carrier solar cells are envisioned to utilize energy filtering to extract power from photogenerated electron–hole pairs before they thermalize with the lattice, and thus potentially offer higher power conversion efficiency compared to conventional, single absorber solar cells. The efficiency of hot-carrier solar cells can be expected to strongly depend on the details of the energy filtering process, a relationship which to date has not been satisfactorily explored. Here, we establish the conditions under which electron–hole separation in hot-carrier solar cells can occur reversibly, that is, at maximum energy conversion efficiency. We thus focus our analysis on the internal operation of the hot-carrier solar cell itself, and in this work do not consider the photon-mediated coupling to the Sun. After deriving an expression for the voltage of a hot-carrier solar cell valid under conditions of both reversible and irreversible electrical operation, we identify separate contributions to the voltage from the thermoelectric effect and the photovoltaic effect. We find that, under specific conditions, the energy conversion efficiency of a hot-carrier solar cell can exceed the Carnot limit set by the intra-device temperature gradient alone, due to the additional contribution of the quasi-Fermi level splitting in the absorber. We also establish that the open-circuit voltage of a hot-carrier solar cell is not limited by the band gap of the absorber, due to the additional thermoelectric contribution to the voltage. Additionally, we find that a hot-carrier solar cell can be operated in reverse as a thermally driven solid-state light emitter. Our results help explore the fundamental limitations of hot-carrier solar cells, and provide a first step towards providing experimentalists with a guide to the optimal configuration of devices.
SchmelzsicherungZelle <Mikroelektronik>SonnenenergieFlugzeugträgerTrenntechnikElementarteilchenphysikVideotechnikComputeranimation
Zelle <Mikroelektronik>ElektronSchwarzes LochPhotovoltaikThermoelektrizitätEisenbahnbetriebÖffentliches VerkehrsmittelSchubumkehrEnergieniveauThermikKühlschrankLocherElektronDruckgradientPhotovoltaikanlageBesprechung/Interview
ElektronSchwarzes LochSolarzelleErneuerbare EnergienEisenbahnbetriebLumineszenzdiodeSchubumkehrÖffentliches VerkehrsmittelPhotovoltaikanlageErwärmungStörgrößeTrenntechnikFACTS-AnlageQuantenelektronikThermoelektrizitätDefektelektronLichtFlugzeugträgerGeneratorBlatt <Papier>SonnenenergiePhotovoltaikBesprechung/Interview
EnergielückeThermalisierungRuhestromModellbauerSchmiedenBahnelementSpannungsabhängigkeitPhotovoltaikanlageHalbleiterPhotovoltaikBewegungsmessungThermoelektrizitätTemperaturStoff <Textilien>LocherDiodeKlangeffektElektronHeterostrukturTechnische ZeichnungDiagrammFlussdiagramm
RuhestromOptisches InstrumentThermikUhrwerkFlugzeugträgerElektronLocherOptisches SpektrumAbsorptionSpannungsänderungModellbauerSchaltplanPhotovoltaikFlussdiagramm
Besprechung/Interview
FlugzeugträgerUhrwerkThermoelektrizitätFlugzeugträgerStoff <Textilien>SpannungsänderungSpannungsabhängigkeitFamilie <Elementarteilchenphysik>ComputeranimationFlussdiagramm
Elektrischer StromDiodeLichtLichtLichtquelleDiodeLumineszenzdiodeDiagrammFlussdiagramm
Elektrischer StromDiodeLichtElektrische StromdichteFlussdiagramm
TemperaturgradientElektrizitätBlatt <Papier>AbsorptionHeterostrukturHalbleiterEmissionsvermögenTemperaturBesprechung/Interview
Transkript: Englisch(automatisch erzeugt)
What happens when you combine a thermoelectric device and a photovoltaic device? How do electrons and holes behave in the presence of simultaneous thermal and quasi-Fermi level gradients? If a refrigerator is the reverse mode of operation of a thermoelectric power generator, and a light-emitting diode is the reverse mode of operation of a photovoltaic device,
what is the reverse mode of operation of a combined thermoelectric and photovoltaic device? A refrigerating light-emitting diode? Well, in fact, yes. Yes, it is. These are just some of the questions asked and conclusions reached in our paper, Reversible Electron Hole Separation in a Hot Carrier Solar Cell,
in which we investigate new possibilities for renewable energy device design at the intersection of light, heat, and quantum electronics. To investigate what happens when you combine a thermoelectric device and a photovoltaic device, we employ a simplified model describing the situation, a semiconductor heterostructure NiP diode,
in which the interior intrinsic region is at one temperature, and in which the edge, heavily doped regions, are at another temperature. This constitutes the thermoelectric portion of the model. To add the photovoltaic element and capture the effect of illumination, a chemical potential splitting of the electrons and holes is present in the intrinsic region of the diode.
This describes the non-equilibrium populations of the electrons and holes that are sustained by the absorption of power from the illuminating spectrum. By tracking the change in the entropy of the electrons and the holes as they move within this model system, we find there are new and interesting measurable physical behaviors that would be present in such a system.
Firstly, larger open circuit voltages than are possible in conventional isothermal photovoltaics can be achieved due to the thermoelectric contribution to the device voltage. Secondly, enhanced thermoelectric performance could be obtained due to the additional non-equilibrium of photogeneration of carriers
and the resulting splitting of carrier chemical potentials. Finally, our analysis shows that a heat-powered light emitting diode could be constructed in which light emission is caused by radiatively recombining thermocurrents. These results suggest that some very interesting experiments may be possible by simultaneously studying temperature gradients, light absorption and emission,
and electrical transport in semiconductor heterostructure devices. Surely, there are physical challenges to the realization of such systems, but whoever said science was easy? I hope you enjoy our paper. Happy reading!