Bimolecular recombination in polymer/fullerene bulk heterojunction solar cells

Abstract

Bimolecular recombination in organic semiconductors is known to follow the Langevin expression, i.e., the rate of recombination depends on the sum of the mobilities of both carriers. We show that this does not hold for polymer/fullerene bulk heterojunction solar cells. The voltage dependence of the photocurrent reveals that the recombination rate in these blends is determined by the slowest charge carrier only, as a consequence of the confinement of both types of carriers to two different phases.

Origin of reduced polaron recombination in organic semiconductor devices

“…6,16 is very well reproduced by the simulations. As pointed out above, the models by Koster et al 15 and Adriaenssens and Arkhipov 11 were not able to describe this temperature dependence. Thus, our model is the first one to describe the experimentally found temperature dependence of the reduced Langevin recombination qualitatively.…”

“…In order to recombine, a potential barrier proportional to the energy difference between the minimum and maximum of the 6 and of Juska et al 16 (circles). The models by Koster et al 15 (dashed) and Arkhipov et al 11 (dotted) are also included; they show a markedly different temperature dependence as compared to the experimental data.…”

“…The model introduced by Koster et al 15 is an extension of the Langevin model. It considers an inherent property of bulk heterojunction solar cells: the phase separation of donor and acceptor materials ( Fig.…”

“…For the third order recombination, the scenario of a carrier concentration or time dependent bimolecular recombination should be considered, and is probably related to a Electronic address: deibel@physik.uni-wuerzburg.de delayed recombination due to trapping in the tail of the density of states. 14 Concerning the reduced recombination rate, two models 11,15 have been proposed in literature trying to explain the reduction mechanism. However, as we pointed out recently, 6 both fail to predict the correct temperature depenence.…”

Charge generation in polymer–fullerene bulk-heterojunction solar cells

“…[89][90][91][92] In macroscopic modeling, the electron and hole mobilities are usually fitted from the space-charge-limited current regime of the single-carrier devices, while the geminate recombination (GR) rate is used as a fitting…”