Dresden 2017 – wissenschaftliches Programm
CPP 41.1: Hauptvortrag
Mittwoch, 22. März 2017, 15:00–15:30, ZEU 260
The role of incoherent hopping in the photogeneration of charges in organic semiconductors — •Anna Köhler — University of Bayreuth, 95400 Bayreuth, Germany
We demonstrate that efficient and nearly field-independent charge separation in organic planar heterojunction solar cells can be described by an incoherent hopping mechanism that can be modelled by kinetic Monte Carlo simulations that include the effect of on-chain delocalization. We address, first, the issue of differentiating between geminate and nongeminate recombination in solar cells.( Adv. Funct. Mater. 2016, DOI: 10.1002/adfm.201604906) We show that a reduced fill factor and the appearance of an s-shaped I-V curve even at low light intensities results from geminate recombination due to the back diffusion of holes toward their siblings at the donor-acceptor interface rather from to charge accumulation at the donor-acceptor interface. Second, we consider how optical excitation of C60 and PCBM contribute to the photogeneration of charge carriers. (J. Phys. Chem. C 2016 DOI: 10.1021/acs.jpcc.6b0847). We find that intrinsic photogeneration starts at a photon energy of about 2.25 eV, i.e., about 0.4 eV above S1. It originates from charge transfer type states that can autoionize incoherently via thermalization before relaxing to S1 state, in the spirit of Onsager's 1938 theory.