Preparation And Optical Properties Of Poly (3-Hexylthiophene) And ZnO Micro/Nanospheres Composite Films

In numerous alternative energies, solar energy with its clean, plentiful, renewable characteristics is more and more in people’s graces. The most important way of solar energy utilization is to design and produce high conversion efficiency solar cells. Recently, organic/inorganic hybrid solar cells based on electron-donating conjugated polymers and electron-accepting inorganic nanocrystals have attracted public attention. Alternatively, inorganic nanocrystals such as TiO2, CdSe and ZnO can be used as electron acceptors in hybrid solar cells, which exhibit higher mobility, stability and lower cost. Among these inorganic nanocrystals, ZnO is believed to be one of the most promising electron acceptors owing to its environment of friendliness and low crystallization temperature. However, the intrinsic surface defects of ZnO nanocrystals make the final power conversion efficiency (PCE) of hybrid solar cells lower. So it is necessary to carry on the surface modification of ZnO, which will exert to improve its dispersion in the blending system and enhance the PCE of the hybrid solar cells.First, ZnO micro/nanospheres were synthesized by one-step hydrothermal method, in which the influences of hydrothermal temperature (80,100, and120℃), hydrothermal time (1,2, and4h), triethanolamine (TEA) and water with different volume ratio (1:12,1:6,1:4, and1:2) on the morphology of ZnO were discussed. Second, ZnO micro/nanospheres were modified by surfactant polyethylene glycol (PEG), in which the influences of PEG molecular weight (2000,6000, and20000), and PEG dosage (2.5%,5%, and10wt%of ZnO) on the ZnO film were investigated. Then, the relationship between energy level structure of ZnO (or PEG-modified ZnO) micro/nanospheres and photoelectric performance was investigated. Finally, P3HT/ZnO and P3HT7PEG-modified ZnO composite films were prepared by physical blending and spin-coating method using ZnO micro/nanospheres or PEG-modified ZnO micro/nanospheres and poly (3-hexylthiophene)(P3HT) mixture chlorobenzene solution, in which the influences of P3HT concentration (6,12, and18mg/mL), blending mass ratio (4:1,2:1,1:1, and1:4), spin-coating speed (1000,1500, and2000rpm) and annealing temperature (90,120, and150℃) were discussed. The optical performances of two kinds of composite films were investigated. This lay an experimental and theoretical foundation for the next preparation of P3HT/ZnO micro/nanospheres hybrid solar cells. The main conclusions are as follows:1. The hydrothermal temperature and hydrothermal time had little effect on the diameter of the ZnO micro/nanospheres within the scope of experiment, and the size and morphology of ZnO micro/nanospheres were effectively controlled by adjusting the volume ratio of triethanolamine (TEA) to H2O. With the increase of TEA amount in the reaction, the diameter of the ZnO micro/nanospheres increased. However, with further increasing to a certain amount, the morphology of ZnO turned to a triangle shape. ZnO micro/nanospheres had uniform size and good dispersion when hydrothermal temperature was100℃, hydrothermal time was2h, and the volume ratio of TEA to H2O was1:12.2. Compared with pure ZnO film, P3HT/ZnO micro/nanospheres composite film had broader ultraviolet absorption range, stonger adsorption of sunlight, suggesting that the absorption spectra had good match with the solar spectra. The order of P3HT was enhanced by annealing treatment. Thus the crystallization of the composite film was improved, which is conducive to enhance the efficiency of the hybrid solar cells. The optimal preparation of composite films was spin-coating from12mg/mL P3HT, with mass ratio of1:2, under1500rpm, and120℃annealing treatment for10min.3. ZnO micro/nanospheres modified by PEG with molecular weight6000and dosage of5wt%had regular morphology and improved dispersion in chlorobenzene. It is feasible that the modified ZnO micro/nanospheres were used as an electron acceptor because of their energy level matching with P3HT. Compared with P3HT/ZnO composite film, P3HT/PEG-modified ZnO had more regular surface, less surface defects, better absorptivity and higher fluorescence quenching, which are conducive to the absorption of sunlight and the exciton dissociation and transport.