Nongeminate recombination in organic bulk heterojunction solar cells: Contribution of exciton–polaron interaction

Abstract

A new model to explain nongeminate recombination in organic bulk heterojunction solar cells is presented. We suggest that the annihilation of excitons on charge carriers at the interface between donor and acceptor phases competes with the bimolecular recombination of Coulombically bound electron–hole pairs. The exciton–polaron interaction gives visible contribution to the reduction of Langevin recombination. An analytical formula, which describes the reduction prefactor, has been derived. We demonstrate that exciton–charge carrier interactions cause an increase of the recombination order. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Four-body recombination in organic bulk heterojunction solar cells: an alternative interpretation

“…Recently, it has been experimentally proved that the Langevin mechanism cannot fully describe the nongeminate recombination process in organic bulk heterojunction structures. In order to explain the loss of photocurrent in such systems, different theoretical concepts have been reported [1][2][3][4][5][6][7][8][9][10][11]. However, the origin of this effect still appears to be questionable.…”

Benchmarking the Electronic Processes at the Planar Organic Heterojunction Solar Cells

“…In the suggested model (Figure ), we propose a third loss mechanism, which is associated with charges (polarons) annihilating excitons before they may contribute to the charge generation process. ,,, The relevant rates are K ep and K CTp for the exciton and CT (exciton), respectively. This process is well documented in the literature so there is no doubt that to some extent it is taking place .…”

“…There has been extensive modeling effort toward the understanding of bulk heterojunction solar cells, − while there are significantly fewer reports regarding the planar heterostructure device. − However, the planar heterostructure better lends itself for the understanding of the underlying physics. In the planar heterostructure, one can almost intuitively separate between charge-transport and the generation-recombination processes (see Figure b), thus allowing for critical examination of the processes taking place at the heterojunction.…”

Electrostatic interface recombination in the system of disordered materials characterized by different permittivities

“…We can see that decreases with a concentration of charge carriers for both mobilities t and . The comparison demonstrates that calculated for overall mobility is larger than obtained for bound pairs near the interface of donor-acceptor phases in organic bulk heterojunction solar cells [15,16]. For further analysis, we have decided to determine orders of recombination in the concentration range between 10 14 -5×10 16 cm −3 to show the impact of tail and deep localized states.…”