Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 39: Photovoltaics: Chalcopyrites I
HL 39.6: Talk
Tuesday, March 15, 2011, 14:45–15:00, FOE Anorg
Spatially and time resolved cathodoluminescence spectroscopy of CuGaSe2 — •Torsten Schwarz1, Mathias Müller1, Frank Bertram1, Jürgen Christen1, Daniel Abou-Ras2, Thorsten Rissom2, Thomas Unold2, and Hans-Werner Schock2 — 1Otto-von-Guericke-University Magdeburg, Germany — 2Helmholtz Zentrum Berlin for Materials and Energy, Germany
The luminescence properties of polycristalline CuGaSe2 as an efficient absorber material for thin film solar cells has been studied comprehensively using spatially and time resolved cathodoluminescence (CL) spectroscopy. The Mo/glass substrate of a complete solar cell grown by a three-stage process was lifted off to investigate the back side of the absorber layer. CL spectra recorded at 6 K, exhibit a strong, dominating emission at 1.64 eV. In addition, an emission peak around 1.57 eV as well as a peak around 1.45 eV is found in several microscopic regions. In excitation density dependent CL measurements a blueshift of 6.4 meV/decade and 4.3 meV/decade for the peaks at 1.64 eV and 1.57 eV is observed as well as a sublinear increase of the peak intensities with slopes of 0.66 and 0.77. ps-time resolved CL was performed using a long rectangular shaped electron excitation pulse of 710 ns width to ensure reaching steady state and a low repetition rate (200 kHz) to reach the thermal equilibrium between the pulses. A redshift in onset (6 meV) and decay (36 meV) is found. Furthermore, monochromatic transients show an increase of the initial lifetime of carrier recombination processes from 10 ns at 1.67 eV up to 150 ns at 1.55 eV. Both are characteristic fingerprints for strong relaxation processes.