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Impact of Ground‐State Charge Transfer and Polarization Energy Change on Energy Band Offsets at Donor/Acceptor Interface in Organic Photovoltaics
Author(s) -
Akaike Kouki,
Kanai Kaname,
Ouchi Yukio,
Seki Kazuhiko
Publication year - 2010
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200901585
Subject(s) - materials science , organic solar cell , acceptor , dipole , exciton , x ray photoelectron spectroscopy , vacuum level , homo/lumo , chemical physics , ground state , polarization (electrochemistry) , optoelectronics , atomic physics , molecule , condensed matter physics , chemistry , nuclear magnetic resonance , organic chemistry , polymer , physics , quantum mechanics , composite material
The fullerene (C 60 )/copper phthalocyanine (CuPc) interface is one of the widely used donor/acceptor (DA) interfaces for organic photovoltaics (OPVs), and information on the electronic structure at the interface is essential for fully understanding the energetics of excitons and carriers in OPVs. Here, an investigation into the energy levels at the C 60 /CuPc interface is made using UV photoelectron, X‐ray photoelectron, and inverse photoemission spectroscopies. The vacuum level and core levels rise with C 60 deposition on the CuPc film, which indicates that the interfacial dipole is formed with the negative charge on the C 60 side. The interfacial dipole can be formed by the electron transfer from CuPc to C 60 in the ground state at the interface, which is indicated by the analysis of the UV–vis–NIR absorption spectrum of the CuPc/C 60 blended film. On the other hand, the highest occupied and lowest unoccupied molecular orbitals of CuPc and C 60 shift in opposite directions at the interface. This is attributed to the changes of the polarization energies of CuPc and C 60 at the interface. The formation of the interfacial dipole and the change of the polarization energy result in the anomalous energy band offsets at the C 60 /CuPc interface, which are entirely different from those in inorganic p–n junctions.