[12p-A402-1~17] 12.5 Organic solar cells

[12p-A402-13] Charge dissociation energy for fullerene-based polymer solar cell

Hiroyuki Ichikawa¹, Itaru Osaka², Tomohiro Fukuhara³, Yasunari Tamai^3,4, Hideo Ohkita³, 〇Hiroyuki Yoshida^1,5 (1.Chiba Univ., 2.Hiroshima Univ., 3.Kyoto Univ., 4.JST PRESTO, 5.MCRC, Chiba Univ.)

Keywords:organic solar cell, low-energy inverse photoelectron spectroscopy, exciton binding energy

One of the significant features of organic semiconductor is its small electric-field screening owing to the low permittivity and charge carrier localization. In organic solar cells (OSCs), the hole-electron pair of the charge-transfer (CT) at the D/A interface should overcome the strong Coulomb force to separate into free carriers (FC). Although numbsers of studies has been devoted to elucidate mechanism for the charge separation for a decade, no conclusion has been reached. One of the reasons is a lack of precise value for the charge-separation energy (the energy barrier from the CT to FC states). In this study, we applied our experimental technique, low-energy inverse photoelectron spectroscopy (LEIPS), together with ultraviolet photoelectron spectroscopy (UPS) to D/A blend films for high-efficiency fullerene OSCs with low- and normal-energy loss. We determined the FC state energy and the energy barriers (enthalpy barrier) for the charge separation for the first time.