Polythiophene Ordered Microstructures And Organic Solar Cells Prepared By Electrodeposition

As the storage of fossil type energy sources (i.e. coal, oil and natural gas) decreases and the global energy demand continues to increase, it's urgent to develop new energy supply for replacement. Exploiting and developing the solar energy as a substitute is a promoting route. Comparing with the traditional silica solar cells, organic solar cell is low-cost, highly flexible and green, so the research in this field has caused widely attention. Within the past three decades there has been a tremendous effort to develop organic solar cells, starting with the application of small organic molecules (pigments), and later with semiconducting polymers, remarkable improvements have been reported within the last decade. From device structure point of view, the first generation of organic photovoltaic solar cells was based on single organic layers sandwiched between two metal electrodes of different work functions. The rectifying behavior of single-layer devices was attributed to the asymmetry in the electron and hole injection into the molecular orbitals and to the formation of a Schottky-barrier between the p-type organic layer and the metal with the lower work function. In this case, the organic layer was sandwiched between a metal–metal oxide and a metal electrode, thus enhancing the Schottky-barrier effect. The second generation of organic solar cells was based on a stacked bilayer of two organic materials (p-type and n-type semiconductor respectively) sandwiched between a transparent conducting oxide anode and a metal cathode. This charges was achieved at the interface of two layers. The most efficient organic solar cells were base on bulk heterojunction which was prepared by mixing the p-type and n-type materials together. From device processing point of view, the vacuum deposition method and spin-coating method were most wildely applied.This thesis is mainly discussing how to prepare efficient organic solar cells via electrochemical method and how to ameliorate the light absorption for efficient organic solar cell processing with the focus on electrodepostion and organic solar cell. To achieve the fist goal, a series of electrochemical experiments were conducted to investigate the film-processing technique and property of resulted films. Some polythiophene with special nano-micro structures was prepared. After that, the electrodeposition technique was applied to fabricate organic solar cells. The relative experimental situations and affecting parameters were investigate to optimize performance of the orgaic solar cells. Then we used highly conductive PEDOT:PSS as anode and fused silica as substrate to optimize organic solar cell prepared by spin-coating method. The impact of transmission enhanced texture on was investigated. More details are now listed below,1. Utilizing polystyrene colloidal crystal as scacrifice template, we fabricated polythiophene inverse opal film, polythiophene inverse opal grating, polythiophene/polystyrene compound microspheres and porous polythiophene microspheres by electrodepositing method. The proper experimental condition was found and the morphology and structure of various products was investigated. The polythiophene inverse opal film and grating have ideal structure which makes them suitable for photonic crystals. The polythiophene/polystyrene microspheres is a novel type colloidal particles which has high conductivities and is sure to have wide application fields such as photoelectronic devices, sensor and catalysis. We analyzed its morphology and composition, after comparison the difference between polythiophene/polystyrene microspheres and hemisphers, we proposed the mechanism of polythiophene/polystyrene microspheres. We found that the growth process is closely connected with the scatted active sites of ITO glass, the kinetics of electrodeposition, the defects in colloidal crystal template and the negative charge on PS colloidal particles.2. We constructed a bilayer solar cell by a two-step process which combined electrodepositing polythiophene in acetonitrile solution and spin coating PCBM from chloroform together. The influence of polythiophene thickness on solar cell performance was investigated. The performance of the solar cell was greatly enhanced compared with the electrodeposited polythiophene single layer device. The power conversion efficiency of 0.1% under AM1.5 (100 mW cm-2) was acquired when the thickness of polythiophene and PCBM were 15 nm and 30 nm, respectively. This bilayer heterojunction solar cell fabricated by electrodeposition and spin coating techniques provides a new approach for the processing of large scale organic solar cells.3. Surface with transmission enhanced texture (TET) composed of hexagonal packed"moth eye"shaped protuberances on fused silica was prepared and its effect on transmittance was investigated. The TET structure can effectively improve the performance of organic solar cells on fused silica substrates using highly conductive PH500 as anode. The increased short-circuit current density and power conversion efficiency confirms that TET structure can effectively improve the transmittance of the substrate and the anode, which further enhanced the light absorbance of the active layer. This experiment offers a solution to improve the efficiency of organic solar cells by optimizing the optical design of substrate materials.