Dresden 2017 – wissenschaftliches Programm
CPP 41.4: Vortrag
Mittwoch, 22. März 2017, 16:00–16:15, ZEU 260
Role of trapped and free charges on the recombination in a low band-gap organic solar cell — •Steffen Roland1, Antonio Facchetti2, and Dieter Neher1 — 1University of Potsdam, Institute of Physics and Astronomie, Potsdam, Germany — 2Northwestern University, Department of Chemistry, Evanston, IL-USA
While the role of traps on the transport of photogenerated charges has been analyzed in detail in the literature, the effect of energetic disorder on the rate of non-geminate recombination is yet not very clear. In this talk a new comprehensive approach of how to treat recombination in energetically disordered organic solar cells is proposed. Charge extraction techniques are used to examine the recombination dynamics of a typical organic solar cell (PMDPP3T:PCBM) in detail. While temperature dependent steady-state charge extraction experiments predict a significant amount of trapped charges, it is found that the recombination current (JR) is dominated by a bimolecular process. A model is introduced in which free charges (outside the Fermi-gap) that contribute to JR are discriminated from trapped charges (inside the Fermi-gap), which do not contribute to JR. The free charge carrier recombination coefficient is determined by time delayed collection field measurements and used to accurately fit the measured JV-characteristics over a wide range of light intensities. These results prove that in this system, although charges undergo trapping, the recombination current is dominated by free bimolecular carrier recombination. This work sheds new light on the influence of trapped charges on the recombination process, a topic that has yet remained controversial within the field.