Preparation and Photovoltaic Properties of Orientation-controlled Perylenetetracarboxylic Diimide Films

Abstract

N, N'-Dimethylperylene-3, 4: 9, 10-tetracarboxylic diimide (Me-PTC) was vapor-deposited on an ITO glass, a poly (tetrafluoroethylene) (PTFE) -coated glass and a KBr substrate. The film deposited on an ITO glass was composed of randomly oriented crystallites. On the other hand, Me-PTC grew epitaxially on a PTFE-coated glass and a KBr substrate. The Me-PTC crystals deposited at 100 and 150 °C were oriented with respect to the substrate crystal in the following epitaxial relatins: [010] (001)_Me-PTC//[001] (100) P _TFE-15°C, [010] (001)_Me-PTC//[110] (001)_KBr-100°C, (102)_Me-PTC//(001)_KBr-150°C and [010]_Me-PTC//[110]_KBr-150°C=±15°. The photovoltaic properties of the Me-PTC films were investigated in the ITO/ Me-PTC/I₃^-, I^-/ Pt wet system. The current-voltage measurement in the dark indicated a rectifying behavior due to an n-type semiconduction of Me-PTC. Under illumination, anodic photocurrents were observed. However, photocurrents decreased gradually and cathodic photocurrents were observed finally. The conduction type of Me-PTC film changed from ntype to p-type by the doping of iodine in the solution. The photovoltaic parameters of the epitaxial films were 3 times larger than those of the randomly oriented films. It was very important to control not only the molecular orientation but also the grain size in order to enhance the photovoltaic properties of Me-PTC film.