Abstract
We investigate the dependence of the characteristics of polymer photovoltaic cells on the concentration of doping of the active layers by heavy-metal complexes. We wish to exploit the strong spin-orbit coupling of such complexes to induce a relatively fast exciton intersystem crossing from the singlet to the longer-lived triplet manifold, to increase in turn the lifetime of the exciton, its diffusion length, and thus the probability of dissociation and the overall device conversion efficiency. We combine current-voltage curves, photocurrent spectra, and atomic force micrographs to show that there is an optimum doping load above which the device performance severely deteriorates. We find, for an Ir-pyridine dopant, a maximum load of approximately 5%. (C) 2011 American Institute of Physics. [doi:10.1063/1.3665688]