Synthesis And Organic Photovoltaic Properties Of Perylene Mono/Diimides Derivatives

Perylene diimides (PDIs), as an N-type organic semiconductor materials, are received extensive attention because of their high molar extinction coefficient, strong absorption and strong ability to accept electrons, high fluorescence quantum yield, high electron mobility, good optical and electrochemical stability, facile modified structure, etc.. Hence, PDIs are very important acceptor materials in organic solar cells (OSCs). In this dissertation, according to organic photovoltaic (OPV) device theory, we design and synthesize a series of perylene mono/diimide derivatives, and carry on a research on photophysical properties, thermal stability, and performance of BHJ solar cells.1. Acceptor material15-22are designed and synthesized. And their photophysical properties and thermal stability are studied systematically. They have strong absorption, ability of accept electrons and good thermal stability. Space-charge-limitted current (SCLC) measure indicates that17:P3HT film exhibits relatively higher electron mobility, up to9.85x10-5cm/(V s).15-22as acceptors and P3HT as donor material, after annealing at150℃, the optimum PCE of17:P3HT cell is up to2.30%with open circuit voltage (Voc) of1.00V. And photocurrent density, atom force microscope (AFM) surface morphologis and impedance spectroscopy demonstrate that charge separation efficiencies, surface roughness and interfcae resistance have a very important impact on the performance of OSCs.2. Model compound26is synthesized by one or two-step procedure, using light-induced ring-closure reaction involving Schiff base. Thereby, according to model compound26’ reaction process, compound31(31’) with double N aza-ring rigid planar conjugated system, is synthesized by light irradiation. And compound31(31’) is characterized by UV-vis absorption spectrum, fluorescence emission and electrochemistry. Scanning electron microscope (SEM) image dispalys that compound31a (31a’) shows a self-assembled morphology composed of nanobelts which are conducive to electronic transmission and could improve film-forming property of molecule. Its electron mobility is measured by SCLC model, involving four different thickness films. The electron mobility of487nm film thicknesses is highest, a value of5.65×10-4cm2/(Vs).3. A novel ladder-conjugated star-shaped macromolecule acceptor material40, with four perylene diimide (PDI) branches and a fluorene core, is efficiently synthesized. It has highly soluble in dichlorobenzene with the solubility of155mg/mL, higher than these of PDI (35mg/mL) and39(70mg/mL). Macromolecule40exhibits excellent thermal stability with the decomposition temperature (Td) of291.2℃, which is65℃higher than that of PDI, demonstrated by thermogravimetric analysis (TGA).The cyclic voltammetry (CV) is employed to investigate the electrochemical properties. Even if the CV curves of macromolecule40are successively scanned for15cycles, it still remains invariable reduction potentials. It also shows outstanding photostability, even better than PDI, which maintains99%fluorescence intensity after irradiation for10min using maximum laser intensity. In the steady-state SCLC devices, molecule40exhibits higher intrinsic electron mobility of2.22×10-5cm2V-1s-1,3orders of magnitude over that of PDI (3.52×10-8cm2V-1s-1). The BHJ organic solar cells (OSCs) using molecule40as acceptors and P3HT as donors obtain optimum power conversion efficiency (PCE) of0.64%, which is64times that of the PDI:P3HT BHJ cells.4. We propose the application of liquid crystalline acceptors as a potential means to improve the performances of BHJ organic solar cells. Molecule43, a structurally-simple PDI, has been adopted as a model for thorough investigation. It exhibits a broad temperature range of liquid crystalline (LC) phase from41℃to158℃, and its LC properties have been characterized by Differential Scanning Calorimetry (DSC), polarizing microscope (POM) and X-ray diffraction (XRD). The BHJ devices using P3HT:43(1:2) as organic photovoltaic active layer undergoing thermal annealing at120℃, shows an optimized efficiency of0.94%. By contrast, the devices based on molecule41, a non-liquid crystalline PDI counterpart, only obtain a much lower efficiency of0.22%. AFM images confirm that the active layers composed of P3HT:43have smooth and ordered morphology. In SCLC devices fabricated by spin-coating technique, molecule43shows the intrinsic electron mobility of2.85×10-4cm2/(V s)(at0.3MV/cm) which is almost5times that of molecule41’s5.83×10-5cm2/(V s) under the same conditions for thermal annealing at120℃.