Abstract
This article reports an improvement of photovoltaic response by dispersing phosphorescent Irppy3
molecules in an organic solar cell of poly2-methoxy-5-2-ethylhexyloxy-1 4-phenylenevinylene
MEH-PPV blended with surface-functionalized fullerene 1-3-methyloxycarbonylpropy1-phenyl
6,6 C61 PCBM. The magnetic field–dependent photocurrent indicates that the dispersed Irppy3
molecules increase the spin-orbital coupling strength with the consequence of changing the singlet
and triplet ratios through intersystem crossing due to the penetration of the delocalized electrons
of MEH-PPV into the large orbital magnetic field of Irppy3 dopants. The tuning of singlet and
triplet exciton ratios can lead to an enhancement of photovoltaic response due to their different
contributions to the two different photocurrent generation channels: exciton dissociation and
exciton-charge reaction in organic materials. In addition, the photoluminescence temperature
dependence reveals that the dispersed Irppy3 reduces the recombination of dissociated charge
carriers in the PCBM doped MEH-PPV. As a result, adjusting singlet and triplet ratios by
introducing heavy-metal complex Irppy3 provides a mechanism to improve the photovoltaic
response through controlling exciton dissociation, exciton-charge reaction, and recombination of
dissociated charge carriers in organic bulk-heterojunction solar cells.