Offset energies at organic semiconductor heterojunctions and their influence on the open-circuit voltage of thin-film solar cells

Organic semiconductor heterojunction (HJ) energy level offsets are modeled using a combination of Marcus theory for electron transfer, and generalized Shockley theory of the dark current density vs voltage $(J\text{\ensuremath{-}}V)$ characteristics. This model is used to fit the $J\text{\ensuremath{-}}V$ characteristics of several donor-acceptor combinations commonly used in thin film organic photovoltaic cells. In combination with measurements of the energetics of donor-acceptor junctions, the model predicts tradeoffs between the junction open-circuit voltage $({V}_{\mathrm{OC}})$ and short-circuit current density $({J}_{\mathrm{SC}})$. The ${V}_{\mathrm{OC}}$ is found to increase with light intensity and…

• AF
  Air Force Office of Scientific Research
• NR
  National Renewable Energy Laboratory