Open circuit voltage ͑V oc ͒ of organic photovoltaic devices has been interpreted with either the metal-insulator-metal ͑MIM͒ model or the energy offset between highest occupied molecular orbital ͑HOMO͒ of the donor and the lowest unoccupied molecular orbital ͑LUMO͒ of the acceptor ͑HOMO D -LUMO A ͒. To elucidate the relation between V oc and the two models, we have used electrodes of a wide range of work functions to connect the CuPc/C60 organic photovoltaic devices. We found that when the work function difference ͑⌬ electrodes ͒ between ITO and Al electrode is in the range Ϫ3 and 0 eV, V oc increases linearly with ⌬ electrodes as prescribed by the MIM model. Outside this range, V oc saturates with values close to that given by the HOMO D -LUMO A less the exciton binding energy.

The plasmon resonance and electric field enhancement in a side-by-side tangent nanospheroid homodimer (TNSHD) have been investigated theoretically by using DDA and FDTD methods, respectively. The simulation results indicate that this side-by-side TNSHD has its novel optical properties. We find that the plasmon resonance with a distinct Fano lineshape can be achieved and the electric field intensity can be enhanced strongly. The tunability of the Fano resonance could provide important applications in biosensing. The obtained electric field enhancement might open a promising pathway for surface-enhanced Raman scattering (SERS) and light trapping in solar cells.