In the first chapter we saw that our present energy economy cannot continue in its current form, because we are in the process of changing the environment in which we live. Mankind and all other forms of life have developed over millions of years by adapting to the conditions around us in a continuous process […]

A considerable loss of energy in a solar cell is due to the photons with energy hCO < 8g which are not absorbed. It would be very convenient if two or more of these useless photons could be converted into one photon with energy h(& > 8g, which could then be absorbed by the solar […]

In Section 3.6.2 we have discussed non-radiative transitions between the bands and an impu – rity level. Impurities with energies for electrons in the middle of the energy gap were found to greatly enhance recombination, which is detrimental for the efficiency. In the analysis, gener­ation of electron-hole pairs by optical transitions was neglected. Now we […]

If interaction with phonons cannot be prevented, thermalization losses can be reduced by dividing the incident spectrum over more than one transition as we have seen with tandem cells. In a three-level system, where the levels can be bands as well, three different transitions may occur in a single material: directly from the lower level […]

For conventional solar cells based on thermalization of electrons and holes in the absorber, complete conversion of chemical energy into electrical energy was achieved by membranes, n-type for the transport of electrons to one contact and p-type for the transport of holes to the other contact. This type of membrane is not sufficient for hot […]

The temperature 7 of the electrons and holes in the absorber can be found very easily from the magnitude of the emitted energy current. In contrast to the interaction with phonons, where at open-circuit the emitted photon current is equal to the absorbed photon current, for impact ionization at open-circuit the emitted energy current must […]

Electrons and holes possessing large kinetic energies as a result of generation by high-energy photons can dissipate their kinetic energy in two ways. One is by elastic collisions with the lattice atoms, in which energy is transferred in small portions to the lattice atoms until thermal equilibrium with the lattice is established. The other is […]

The solar-thermal conversion method of Section 2.1.1 can be modified to be applicable to solar cells. Figure 8.7 illustrates the principle. A focussing optical system is used to concentrate the solar radiation onto an intermediate absorber which, as a result, is heated to the temperature 7. Solar cells with an energy gap Eg are placed […]