Spin-dependent charge transfer state design rules in organic photovoltaics

Publication Type:

Journal Article

Source:

Nat. Commun., nature.com, Volume 6, p.6415 (2015)

ISBN:

2041-1723

Keywords:

2015

Abstract:

Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this
work, we examine recombination losses as a function of the electron-hole
spacing in fluorescent charge transfer states, including direct monitoring
of both singlet and triplet charge transfer state dynamics. Here we
demonstrate that large donor-acceptor separations minimize back transfer
from the charge transfer state to a low-lying triplet exciton 'drain' or
the ground state by utilizing external pressure to modulate molecular
spacing. The triplet drain quenches triplet charge transfer states that
would otherwise be spin protected against recombination, and switches the
most efficient origin of the photocurrent from triplet to singlet charge
transfer states. Future organic solar cell designs should focus on raising
the energy of triplet excitons to better utilize triplet charge transfer
mediated photocurrent generation or increasing the donor-acceptor spacing
to minimize recombination losses.