[15p-2N-1~17] 12.2 Characterization and Materials Physics

▲ [15p-2N-5] An Investigation of the Sub-linear Photon Flux Dependency of Photocurrents in Fullerene Thin Films

〇Richard Murdey¹, Naoki Sato¹ (1.Kyoto Univ.)

Keywords:photoconductivity,C60,traps

In this study, we investigate the relationship between incident photon flux and photocurrent for vacuum deposited, thin fullerene films. Photocurrent action spectra in the region of 1.1 eV – 3.1 eV are measured at incident flux intensities from about 10¹⁸ to 10¹⁹ photons m^-2 s^-1. A power law dependence with an exponent of about 0.6 – 0.7 was found, with substantial sample-to-sample variation. It was discovered that the rise and decay times were not constant but increased with decreasing flux intensity, a feature which practically limits the measurement accuracy at low flux intensities. Our measurements confirm that the exponent of the power law flux dependence is constant for a given fullerene sample over the experimentally-accessible variations in both photon energy and photon intensity. Using this knowledge it is possible to reconstruct an accurate photocurrent spectrum by normalizing against the photon flux raised to this exponent. The close correlation between this flux-normalized photocurrent and the optical absorption confirms that photocurrent in the C₆₀ thin film is of extrinsic rather than intrinsic origin.