The energy level alignments at donor/acceptor interfaces in organic photovoltaics (OPVs) play a decisive role in device performance. However, little is known about the interfacial energetics in polymer OPVs due to technical issues of the solution process. Here, the frontier ortbial line-ups at the donor/acceptor interface in high performance polymer OPVs, PTB7/PC71BM, were investigated using in situ UPS, XPS and IPES. The evolution of energy levels during PTB7/PC71BM interface formation was investigated using vacuum electrospray deposition, and was compared with that of P3HT/PC61BM. At the PTB7/PC71BM interface, the interface dipole and the band bending were absent due to their identical charge neutrality levels. In contrast, a large interfacial dipole was observed at the P3HT/PC61BM interface. The measured photovoltaic energy gap (EPVG) was 1.10 eV for PTB7/PC71BM and 0.90 eV for P3HT/PC61BM. This difference in the EPVG leads to a larger open-circuit voltage of PTB7/PC71BM than that of P3HT/PC61BM.

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The electronic structure of ZnO core−C 60 shell (ZnO@C 60 ) quantum dots (QDs) was investigated with the help of model interface analysis between ZnO QDs and C 60 using in situ ultraviolet and X-ray photoelectron spectroscopy measurements. To form the ZnO QDs/C 60 interface in situ, a vacuum-integrated electrospray deposition technique was employed to simulate the electronic interactions between ZnO QDs and C 60 upon the formation of a ZnO@C 60 core− shell structure. Photoelectron spectra of ZnO QDs/C 60 interface formation were compared with those of ZnO@C 60 QD and pristine ZnO QD films. The results revealed that ZnO QDs and C 60 interacted via electron transfer leading to the change in ionization energy of the surface C 60 . This induced a negligible energy barrier between the lowest unoccupied molecular orbital level of C 60 and the conduction band minimum of ZnO, which led to efficient electron transport through the ZnO@C 60 QDs.

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