SKM 2023 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

HL: Fachverband Halbleiterphysik

HL 38: Functional semiconductors for renewable energy solutions I

HL 38.5: Vortrag

Donnerstag, 30. März 2023, 11:00–11:15, POT 6

Tails states, Voc loss and semiconductor compensation — •Susanne Siebentritt and Omar Ramirez — University of Luxembourg, Laboratory for Photovoltaics

It has been shown for many solar cell absorbers that Voc loss correlates with the Urbach energy, which describes the decay of tail states into the band gap. In chalcopyrites it was furthermore observed that heavy alkali postdeposition treatments reduce both: Urbach energy and Voc loss. This behaviour has been attributed to passivation of grain boundaries. However, recently we have shown, that alkali treatment in single crystalline films without grain boundaries also leads to a reduction of Voc loss and Urbach energies. This behaviour can be traced back to a reduced compensation by increasing the doping level. It is to be expected that a similar mechanism plays a role in polycrystalline films. Part of the dependence of the Voc loss on Urbach energy can be attributed to radiative and non-radiative recombination in and through tail states. However, the dependence is stronger than would be expected from the increased recombination. We now understand that this is due to a simultaneous effect: increasing doping increases Voc and decreases tail states. Thus we propose, that one effect of heavy alkali treatment is due to the observed increase of Na doping inside the grains, because it increases the net-doping, reduces tail states and thereby reduces radiative and non-radiative recombination. All this increases Voc.