Dresden 2017 – wissenschaftliches Programm

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

HL: Fachverband Halbleiterphysik

HL 90: Inhomogeneous Materials for Solar Cells

HL 90.5: Vortrag

Freitag, 24. März 2017, 12:30–12:45, POT 81

Charge Carriers Dynamics in Kesterite Band Tails: From Ultra-fast Trapping via Hopping Transport to Cryogenic Microsecond Recombination — •Hannes Hempel¹, Rainer Eichberger², and Thomas Unold¹ — ¹Department structure and dynamics of energy materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany — ²Institute for solar fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany

Kesterite solar cells are known to exhibit band tails originating from atomic disorder. We investigate how these tails affect the dynamics of photo-excited charge carrier by applying transient absorption, time resolved THz spectroscopy and photoluminescence spectroscopy to coevaporated Cu₂ZnSnSe₄ thin film. 100 fs after excitation with 1.5 eV photons the carriers form a hot (>1100 K) Boltzmann distribution in the band states. Within 2 ps they thermalize to lattice temperature and reach simultaneously band edge and tail states. After 10 ps up to 10¹⁷ cm⁻³ carriers are additionally captured into deeper defect states. Then the carriers are distributed in bands, tails and defects and exhibit in average a localized AC-mobility with a DC-value of 100 cm²/Vs. Their transport can be described by a sequence of trapping and detrapping between extended band and localized tail states. At low temperatures the carriers further localize into these tail states which slows down their hopping transport to the recombination sites and increases the measured lifetime from nano to microseconds.