Speaker
Heiner Linke
(Lund University)
Description
Hot carrier solar cells are envisioned to utilize electron
and hole energy filtering in order to extract power from
photo-generated carriers before they thermalize with the
lattice, and thus offer the potential to increase power
conversion efficiency above that of conventional
single-junction solar cells. Here we establish that
strategies previously developed for ideal thermoelectric
devices such as quantum-dot heat engines [1, 2] are also
applicable to hot-carrier solar cells. Specifically, we
establish the condition under which hot-carrier solar cells
can be operated reversibly, namely when charge carriers are
exchanged under conditions of energy-specific equilibrium.
We find that the maximum efficiency of a hot-carrier solar
cell is actually larger than the Carnot efficiency
corresponding to the involved spatial differential in charge
carrier temperature, because of the additional
non-equilibrium represented by the quasi-Fermi level
splitting. We identify separate contributions to the
open-circuit voltage of the hot carrier solar cell from
thermoelectric effects and from electron-hole pair
generation, and quantify its reduction away from the
reversible operation point at points in current-voltage
curve space where carrier extraction takes place under
non-equilibrium conditions.
[1] T.E. Humphrey, R. Newbury, R.P. Taylor, H. Linke, Phys.
Rev. Lett., 89 (2002) 116801.
[2] T.E. Humphrey, H. Linke, Phys. Rev. Lett., 94 (2005) 096601.
