TY - JOUR
T1 - Ultrafast Charge Transfer Dynamics at the Origin of Photoconductivity in Doped Organic Solids
AU - Tsokkou, Demetra
AU - Cheng, Chiao Yu
AU - Krainova, Nina
AU - Mukhopadhyay, Sukrit
AU - Giebink, Noel C.
AU - Banerji, Natalie
N1 - Publisher Copyright:
© 2021 The Authors. Published by American Chemical Society.
PY - 2021/4/8
Y1 - 2021/4/8
N2 - In spite of their growing importance for optoelectronic devices, the fundamental properties and photophysics of molecularly doped organic solids remain poorly understood. Such doping typically leads to a small fraction of free conductive charges, with most electronic carriers remaining Coulombically bound to the ionized dopant. Recently, we have reported photocurrent for devices containing vacuum-deposited TAPC (1,1-bis(4-bis(4-methylphenyl)aminophenyl)cyclohexane) doped with MoO3, showing that photoexcitation of charged TAPC molecules increases the concentration of free holes that contribute to conduction. Here, we elucidate the excited-state dynamics of such doped TAPC films to unravel the key mechanisms responsible for this effect. We demonstrate that excitation of different electronic transitions in charged and neutral TAPC molecules allows bound holes to overcome the Coulombic attraction to their MoO3 counterions, resulting in an enhanced yield of long-lived free carriers. This is caused by ultrafast back-and-forth shuffling of charges and excitation energy between adjacent cations and neutral molecules, competing with relatively slow nonradiative decay from higher excited states of TAPC·+. The light-induced generation of conductive carriers requires the coexistence of cationic and neutral TAPC, a favorable energy level alignment, and intermolecular interactions in the solid state.
AB - In spite of their growing importance for optoelectronic devices, the fundamental properties and photophysics of molecularly doped organic solids remain poorly understood. Such doping typically leads to a small fraction of free conductive charges, with most electronic carriers remaining Coulombically bound to the ionized dopant. Recently, we have reported photocurrent for devices containing vacuum-deposited TAPC (1,1-bis(4-bis(4-methylphenyl)aminophenyl)cyclohexane) doped with MoO3, showing that photoexcitation of charged TAPC molecules increases the concentration of free holes that contribute to conduction. Here, we elucidate the excited-state dynamics of such doped TAPC films to unravel the key mechanisms responsible for this effect. We demonstrate that excitation of different electronic transitions in charged and neutral TAPC molecules allows bound holes to overcome the Coulombic attraction to their MoO3 counterions, resulting in an enhanced yield of long-lived free carriers. This is caused by ultrafast back-and-forth shuffling of charges and excitation energy between adjacent cations and neutral molecules, competing with relatively slow nonradiative decay from higher excited states of TAPC·+. The light-induced generation of conductive carriers requires the coexistence of cationic and neutral TAPC, a favorable energy level alignment, and intermolecular interactions in the solid state.
UR - http://www.scopus.com/inward/record.url?scp=85104916566&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85104916566&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.1c01990
DO - 10.1021/acs.jpcc.1c01990
M3 - Article
C2 - 33859770
AN - SCOPUS:85104916566
SN - 1932-7447
VL - 125
SP - 7086
EP - 7096
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 13
ER -