Modeling of Transient Photocurrent in Organic Semiconductors Incorporating the Annihilation of Excitons on Charge Carriers

The mechanistic study of molecular doping of organic semiconductors (OSC) requiresan improved understanding of the role and formation of integer charge transfer complexes(ICTC) on a microscopic level. In the present work we go one crucial step beyondthe simplest scenario of an isolated bi-molecular ICTC and study ICTCs formed ofup to two (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b,3,4-b”]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)](PCPDT-BT) oligomers and up to two CN6-CP molecules. We find that dependingon geometric arrangement, complexes containing two conjugated oligomers and twodopant molecules can show p-type doping with double integer charge transfer, resulting in eithertwo singly doped oligomers or one doubly doped oligomer. Interestingly, compared to an individualoligomer-dopant complex, the resulting in-gap states on the doped oligomers are significantlylowered in energy. Indicating that, already in the relatively small systems studied here, Coulombbinding of the doping-induced positive charge to the counter-ion is reduced which is an elementalstep towards generating mobile charge carriers through molecular doping.

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Molecular Doping in Multi-Molecule Polymer-Dopant Complexes Shows Reduced Coulomb Binding

10.26434/chemrxiv.12245537 ◽

2020 ◽

Author(s):

Chuanding Dong ◽

Stefan Schumacher

Keyword(s):

Charge Transfer ◽

Organic Semiconductors ◽

Positive Charge ◽

Charge Carriers ◽

Mechanistic Study ◽

Charge Transfer Complexes ◽

Mobile Charge ◽

Molecular Doping ◽

Gap States ◽

P Type

The mechanistic study of molecular doping of organic semiconductors (OSC) requiresan improved understanding of the role and formation of integer charge transfer complexes(ICTC) on a microscopic level. In the present work we go one crucial step beyondthe simplest scenario of an isolated bi-molecular ICTC and study ICTCs formed ofup to two (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b,3,4-b”]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)](PCPDT-BT) oligomers and up to two CN6-CP molecules. We find that dependingon geometric arrangement, complexes containing two conjugated oligomers and twodopant molecules can show p-type doping with double integer charge transfer, resulting in eithertwo singly doped oligomers or one doubly doped oligomer. Interestingly, compared to an individualoligomer-dopant complex, the resulting in-gap states on the doped oligomers are significantlylowered in energy. Indicating that, already in the relatively small systems studied here, Coulombbinding of the doping-induced positive charge to the counter-ion is reduced which is an elementalstep towards generating mobile charge carriers through molecular doping.

Download Full-text