Synthesis And Characterization Of Poly(3-hexylthiophene) Based On Organic-inorganic Solar Cells

In the late 1970s, conjugated polymers were proclaimed as futuristic new materials that would lead to the next generation of electronic and optical devices. It now appears with the discoveries of, for example, polymer light-emitting diodes (LEDs),organic transistors and solar cells. Polythiophenes are an important representative class of conjugated polymers that form some of the most environmentally and thermally stable materials that can be used as electrical conductors, nonlinear optical devices, polymer LEDs, photoresists, antistatic coatings, sensors, batteries, electromagnetic shielding materials, artificial muscles, solar cells, electrodes, microwave absorbing materials, new types of memory devices, nanoswitches, optical modulators, imaging materials, polymer electronic interconnects, nanoelectronic and optical devices, and transistors. Polythiophene and its derivatives work very well in some of the above applications and less impressively in other devices. Creative new design and development strategies of new polythiophenes has led to interesting new materials and enhanced performance in certain devices. The ability of molecular designers to begin to understand how to gain control over the structure, properties, and function in polythiophenes continues to make the synthesis of polythiophenes a critical subject in the development of new advanced materials.Poly(3-alkythiophenes) have good solubility, machinability, solubility, electrically activity, and so on. And their regioregular structure was readily got in addition., so they received so much attraction as donor materials, such as poly(3-hexylthiophene), poly(3-octalthiophene) and poly(3-duodecimalthiophene). Poly(3-hexylthiophene) was known as one of the best electron donor materials among these poly(3-alkythiophenes) because of its regioregular structure, simple synthetical procedures, appropriate solubility, band gap and high hole mobility.An assembly of ITO/nano-crystalline TiO2/polyaniline/ITO has been made in a simple way by our group. The junction thus obtained shows rectifying behaviour. The rectification ratio is more than 160 when the voltage is 2V. Their I–V characteristics indicate a p–n junction at nano-crystalline TiO2/polyaniline interface has been created.Although polyaniline with unique doping method, well electrochemical reversibility, environmental stability, much raw material and simple synthetical method is a promising conductive polymer in practice, the conversion efficiency will still be prevented owing to its unmatched energy level with TiO2,low absorption in visible light and unprocessable. So we decided to choose poly(3-hexylthiophene) to be donor material in the organic-inorganic solar cell system.In the paper monomer 3-hexylthiophenes was prepared according to the procedure of Kumuda and characterized the resultant by using Infrared Spectroscopy and gas chromatography-mass spectrum and the efficiency is about 66%.Next poly(3-hexylthiphene) is polymerized with iron chloride and analyzed by Infrared Spectroscopy,XRD,Ultraviolet-visible Spectroscopy,Atom Force Microscopy,Thermal Gravimetric Analysis and Differential Scanning Calorimetry. From the picture of XRD, it is found that P3HT systhesized by this method takes on non-crystal phase. The formation ofπ overlap along the backbone is confirmed and the regiorandom poly(3-hexylthiophene) has a maximum absorbtion wavelength at～657nm based on ultraviolet-visible spectroscopy ,hence the bandgap of 1.89eV. The poly(3-hexylthiophene) film shows smooth by means of optical microscopy and atom force microscopy and it indicates that poly(3-hexylthiophene) is soluble in common solvent. Thermal gravimetric analysis and DSC reveals that poly(3-hexylthiophene) is stable under heating up lower than 800℃and occurs glass transition at about 195℃.Organic-inorganic photovoltaic devices suffering from lower efficiency than silicon-based photovoltaics have advantages of low cost, processibility, and flexibility and much more attention has been attracted in recent years. The interface between donor and acceptor is critical to the operation of heterojunction photovoitac(PV) cells since excitons are dissociated there, and recombination must be avoided. Titania is a good acceptor semiconductor to use for studies of interface modification because it can be deposited as a solid or nanoporous film, and its surface can be modified easily with many organic molecules that have carboxylic acid groups. Once the interface modifier is attached, polymers can be cast over the structure without removing the modifier due to the large binding constant between carboxylic acid groups and titania.Conductive polymers such as polythiophenes and poly(p-phenylene vinylene)s (PPVs) have been considered as promising light sensitizers and/or charge mediators for realization of efficient photovoltaic performances. Especially, polythiophene is more attractive for nanocrystalline TiO2 PV cells due to its environmental stability and tailorable electrochemical properties.