Abstract:In this study, several naphthalene tetracarboxylic acid diimide (NTCDI) 2 derivatives substituted at the N and N' positions with long normal alkyl chains of different lengths were evaluated as soluble n-type organic thin-film transistor (TFT) materials. NTCDI derivatives with diundecyl (NTCDI-C11), didodecyl (NTCDI-C12), and ditridecyl (NTCDI-C13) exhibited acceptable solubility in chloroform, and their TFTs showed typical n-type TFT performance with relatively high field effect electron mobility (~0.2 cm 2 /Vs) after annealing at a workable temperature of 150 °C. Although NTCDI with dioctyl (NTCDI-C8) showed good solubility in chloroform, the TFT performance of this material was highly inferior to that of NTCDI-C11, NTCDI-C12, or NTCDI-C13. We could not anneal NTCDI-C8 thin films at workable temperatures in vacuo because of sublimation of the material from the substrates. In contrast, NTCDI with dipentadecyl (NTCDI-C15) and dioctadecyl (NTCDI-C18) exhibited both poor solubility for chloroform and poor TFT performance. In short, these compounds are not suitable as soluble n-type organic TFT materials.

We investigated small-molecule-based organic photovoltaic (PV) cells with three different electron-donating material layers, two thiophene/phenylene co-oligomers [-bis(biphenyl-4-yl)terthiophene (BP3T) and -diphenyl sexithiophene (P6T)] and copper phthalocyanine (CuPc), and one electron-accepting material layer (C 60 ). A cascade-type energy relay between the three donor layers occurred, and the incident photon-current conversion efficiency improved in the blue light region, where CuPc has very low optical absorption. An increase in P6T photoluminescence intensity in a 2 two-layer sample (BP3T/P6T) on quartz confirmed interlayer excitation transfer (ET) from BP3T and P6T. The bulk heterojunction architecture in our interlayer-ET-based organic PV cell was effective. Moreover, P6T appeared to have a relatively long exciton diffusion length of several tens of nanometers.

Glass-sandwich-type organic solar cells utilizing liquid crystalline phthalocyanine, 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2), have been fabricated and their photovoltaic properties have been studied. The short-circuit current density (Jsc) and power conversion efficiency (PCE) depend on the C6PcH2 layer thickness, and the maximum performance, such as a Jsc of 7.1 mA/cm2 and a PCE of 1.64%, was demonstrated for a device having a 420-nm-thick C6PcH2 layer. We examined the photovoltaic properties from the viewpoint of the C6PcH2-layer electrical conductance, based on the distribution of the column-axis direction.

Abstract:We demonstrated that N,N′-diphenylperylene tetracarbonic diimide (PTCDI-Ph) could work as an n-type sensitizing layer for the C 60 n-type layer owing to interlayer excitation transfer (ET) when the PTCDI-Ph layer was placed between the C 60 layer and the aluminum anode coupled with the bathocuproine layer. Well-aligned lowest unoccupied molecular orbitals between C 60 and PTCDI-Ph (−4.55 eV for 2 PTCDI-Ph and −4.5 eV for C 60 ) and a larger bandgap for PTCDI-Ph than C 60 (2.04 eV for PTCDI-Ph and 2.0 eV for C 60 ) enabled this interlayer ET-based sensitization. Further, the optical interference effect could be also involved in the sensitization. It was also demonstrated that the combination of both n-type materials C 60 and PTCDI-Ph could successfully reduce the amount of the expensive C 60 used, and a thin C 60 layer was indispensable for efficient charge separation. PTCDI-Ph could work as a light-harvesting n-type material incorporating C 60 -based cells to compensate for C 60 's weak optical absorption.