10.1021/jp506296j.s001 Yufei Zhong Yufei Zhong Seiichiro Izawa Seiichiro Izawa Kazuhito Hashimoto Kazuhito Hashimoto Keisuke Tajima Keisuke Tajima Tomoyuki Koganezawa Tomoyuki Koganezawa Hiroyuki Yoshida Hiroyuki Yoshida Crystallization-Induced Energy Level Change of [6,6]-Phenyl‑C<sub>61</sub>-Butyric Acid Methyl Ester (PCBM) Film: Impact of Electronic Polarization Energy American Chemical Society 2015 polarization energy PCBM molecule photoelectron spectroscopy Electronic Polarization EnergyThe effect Methyl Ester photoemission spectroscopy IP EA film thickness 0.1 eV energy levels electron affinity Precise measurements annealing band gap 2015-01-08 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Crystallization_Induced_Energy_Level_Change_of_6_6_Phenyl_C_sub_61_sub_Butyric_Acid_Methyl_Ester_PCBM_Film_Impact_of_Electronic_Polarization_Energy/2218096 The effect of thermal annealing on the energy levels of [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM) films was investigated using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and low-energy inverse photoemission spectroscopy. We observed that thermal annealing at 150 °C induces reductions of both the ionization potential (IP) and the electron affinity (EA) with a narrowing of the band gap by 0.1 eV. These changes are associated with crystallization and a 2.54% reduction in the film thickness. Precise measurements of both the IP and EA enabled an evaluation of the effects of the electronic polarization energy in a model based on the charge localized in a single PCBM molecule.