Berlin 2015 – wissenschaftliches Programm
TT 60.13: Vortrag
Mittwoch, 18. März 2015, 12:45–13:00, C 130
How intrinsic photo-degradation impacts photovoltaic device performance in organic solar cells — •Thomas Heumueller1, Timothy Burke2, William Mateker2, Michael McGehee2, and Christoph Brabec1,3 — 1Universität Erlangen-Nürnberg — 2Stanford University — 3ZAE Bayern
As organic PV efficiencies exceed 10%, the science of stabilization and lifetime gains importance. Several degradation phenomena in organic solar cells are related to an increase in trap density, but the mechanisms of how different types of traps affect open-circuit voltage, short-circuit current and fill factor need considerably more investigation. To separate effects from several different degradation mechanisms that usually occur at the same time, we perform tests under controlled environmental conditions and distinguish between bulk and interface effects by de-laminating and replacing electrodes. Interfacial degradation is observed to predominantly affect the fill factor, most likely due to the formation of energetic barriers and can be reversed by reapplying new electrodes. Bulk degradation in amorphous systems, like PCDTBT, results in a loss of open circuit voltage. Using charge extraction and transient photovoltage we show that the Voc losses are not caused by increased recombination, but rather by a broadening in the density of states. Crystalline materials demonstrate an increased stability against Voc losses, most likely due to a high charge carrier density at Voc. Sometimes a characteristic loss of short circuit current is observed in crystalline materials. We show that those losses can be prevented by choosing a different acceptor material.