Publication in Physical Review Applied!
This theoretical work shows that an ultrathin solar cell, in this case made of a 12nm InGaAs absorber, can have the operation of a hot carrier solar cell. We considered a quantum electronic transport model, based on non-equilibrium Green's functions, in which are considered the tunneling effect, the quantum confinement, the interactions of electrons with photons and phonons. This model shows that the open circuit voltage Voc varies with the type of considered contact (Fig. 1). We note in particular an increase in voltage when the contact, made of two tunnel barriers, is energy selective. We observe a correlation between this increase and the temperature of the carriers in the absorber. The voltage variation is therefore attributed to a "hot carrier" effect (ΔVoc=41mV for ΔT=131K). Moreover, while the use of an energy selective contact usually results in a strong reduction of the current, this degradation is not observed in our case. A detailed study allows us to highlight a hybridization effect of the absorber states with the selective contact. This hybridization, which is possible because the absorber is a quantum well, allows a very efficient extraction of the photo-generated electrons towards the contact.
Fig. 1: (a) Schematic representation of the considered cells and the current spectra and band diagrams of the cells (b) without selective contact and with a selective contact consisting of a quantum dot of (c) 1.5 nm and (d) 1.2 nm embedded between two AlGaAsSb barriers. Our model allows us to calculate the Jabs generation and Jrec recombination currents. As suggested by the arrows in (b), Jabs corresponds to the positive component of the current (blue) while Jrec corresponds to the negative one (yellow). We also calculate Voc which is estimated by interpolation giving Jabs=Jrec.
Ref : N. Cavassilas, I. Makhfudz, A.-M. Daré, M. Lannoo, G. Dangoisse, M. Bescond, F. Michelini, “Theoretical Demonstration of Hot-Carrier Operation in an Ultrathin Solar Cell,” Physical Review Applied 17 (6), 064001 (2022). https://doi.org/10.1103/PhysRevApplied.17.064001