Correlating First-Principles Electronic Structure with Device Performance of Organic Photovoltaic Cells

Organic photovoltaic cells (OPVs) are promising candidates for low-cost solar energy conversion. Here, we employ static and time-dependent density functional theory calculations to predict the excitation energy of the donor-acceptor charge transfer state (E$_{\textrm{CT}})$ at the interface between C$_{60}$ and several boron(subphthalocyanine)- and azadipyrromethene-based donor moieties, comparing to measured open-circuit voltage (V$_{\textrm{oc}})$ in bilayer heterojunction OPVs [1]. When E$_{\textrm{CT}}$ is approximated as the difference between the ionization potential and electron affinity of the isolated donor and acceptor molecules, respectively, we observe no apparent correlation between E$_{\textrm{CT}}$ and V$_{\textrm{oc}}$. Both bulk polarization and excitonic effects at the interface are found to influence the energetics significantly, the latter being strongly morphology dependent. We demonstrate that a linear relationship between V$_{\textrm{oc}}$ and E$_{\textrm{CT}}$ may be obtained once the interface morphology is considered. We acknowledge support from DOE, NSF-NCN, and NERSC. \\[4pt] [1] C. E. Mauldin \textit{et al.}, ACS Appl. Mater. Interfaces \textbf{2}, 2833 (2010).