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Carrier Tunneling from Charge Transfer States in Organic Photovoltaic Cells
Author(s) -
Devižis Andrius,
Gelzinis Andrius,
Chmeliov Jevgenij,
Diethelm Matthias,
Endriukaitis Laurynas,
Padula Daniele,
Hany Roland
Publication year - 2021
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.202102000
Subject(s) - quantum tunnelling , materials science , electric field , charge carrier , organic solar cell , dissociation (chemistry) , electron , chemical physics , molecular physics , dipole , rectangular potential barrier , atomic physics , condensed matter physics , optoelectronics , physics , chemistry , quantum mechanics , composite material , polymer
Charge transfer (CT) states play a key role in the functioning of organic solar cells; however, understanding the mechanism by which CT states dissociate efficiently into free charges remain a conceptual challenge. Here, the electric field dependent dynamics of charge generation in planar cyanine/fullerene photovoltaic cells is probed over a wide temperature range using time‐resolved Stark effect experiments, transient absorption, and photocurrent measurements. Results indicate that dissociation of thermalized CT states is the rate‐limiting step for all temperatures. The dissociation rate strongly depends on the field, but is temperature independent. The results also suggest that the yield of generated charges is temperature independent. Model electrostatic calculations illustrate that specific orientations of the cyanine crystal relative to C 60 create a repulsive potential for an electron near the interface that is largely due to the quadrupole moment of the unit cell. In combination with the electron‐hole coulomb attraction and the electric field‐induced barrier lowering, a high‐energy potential barrier forms with a narrow width of a few nanometers. It is proposed that charge separation occurs via a field‐dependent electron tunneling mechanism through that barrier, which is temperature independent. The results support a thus far overlooked pathway for CT state dissociation via carrier tunneling.