低エネルギー逆光電子分光法にょる有機半導体の電子親和力の測定技術

摘要

In the operation of organic photovoltaic cells, both the HOMO (occupied) and LUMO (unoccupied) levels are crucial. Although the HOMO levels have been extensively examined using photoemission spectroscopy, there have been no proper methods for the LUMO levels. Recently we have developed a new method, called low-energy inverse photoemission spectroscopy. Low-energy electrons are introduced to the sample surface and photons emitted due to the radiative transition to unoccupied states are detected. From the onset of the spectra, electron affinity is determined within an uncertainty of 0.1 eV. Unlike the conventional inverse-photoemission spectroscopy, sample damage is negligible and resolution is improved by a factor of two. The principle of the present method as well as applications to the studies of organic photovoltaic cells are reported.