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Urbach Energy In CIGS Extracted from Quantum Efficiency Analysis of High Performance CIGS Solar Cells
M. Troviano, K. Taretto
CIGS, Urbach Tails, EQET, IQET Modeling
Thin Films Solar Cells
Subtopic: CIS and Other (II-VI) Ternary Thin Film Solar Cells
Event: 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany
Session: 3BV.5.22
2933 - 2937
ISBN: 3-936338-25-6
Paper DOI: 10.4229/24thEUPVSEC2009-3BV.5.22
0,00 EUR
Document(s): paper


We develop a method to extract the characteristic energy of the Urbach energy band tails in thin film CIGS. By modeling the temperature-dependent internal quantum efficiency (IQET) of CIGS solar cells including sub–gap absorption, we identify a linear region in a semilogarithmic IQET vs. photon energy plot, which yields the Urbach energy EU. Measurements of high efficiency (18 %) CIGS solar cells prepared at the Institut für Physikalische Elektronik (Stuttgart, Germany), yield room temperature Urbach energies around 30 meV in cells with a Ga/(In+Ga) ratio of 0.35. Cryostat temperature-dependent IQET measurements yield an increasing value of EU from 31 meV at 146 K up to 40 meV at 293 K. Additionally, a conversion from IQET to electroluminescence reveals defect bands obtained by other groups with spectroscopic measurements.