Graphene Materials For The Interface Modification Layer Of Polymer Solar Cells

In recent years, polymer solar cells has become one of the hotspots of the scientific community, the efficiency of polymer solar cells has been improved rapidly. The highest efficiency in literature has exceeded 11%. However, comparison with the commercialized inorganic solar cells, the efficiency and stability of polymer solar cells need to be further improved. There are several methods to improve the efficiency of the polymer solar cells: 1, design and synthesis novel conjugated polymers with proper bandwidth, for the maximum absorption of the sunlight; 2, control the nano morphology of bulkheterojunction in the active layers, to enhance the efficiency of exciton dissociation and charge transport and reduce combination loss; 3, optimize the interfaces between electrodes and bulkheterojunctions, to improve the efficiency of charge evacuation from active layers to electrodes.In the dissertation, several graphene derivatives are synthesized, and applied into polymer solar cells as hole transport layers, to improve the efficiency of polymer solar cells:1. Using N, N- dimethylformamide(DMF) or ultra-pure water as a solvent, ethylenediamine as the reducing agent, prepared the amide graphene oxide(named as rGO/DMF and rGO/H2O). Settling test shows the dispersion of rGO/DMF is better than that of rGO/H2 O. Drying causes the reducing of dispersion properties. Infrared spectroscopy and elemental analysis showed that the reaction time longer, the degree of reduction higher in DMF system while it is unconspicuous in H2 O system. The concentration of these rGOs in DMF or H2 O is too low to form continuous films, therefore, they cannot be used as the interface modification layer of polymer solar cells.Using ultra-pure water as a solvent, sodium acid as reducing agent, we prepared carboxy graphene oxide(GO-COOH) material. Infrared spectra showed that the C-OH groups have been substituted with COOH on graphene oxide surface, and AFM tests showed that carboxy graphene oxide enables to reduce the roughness of the surface of ITO. As an anode interface layer applied to the polymer solar cell device, the energy conversion efficiency of the device is increased from 0.89 to 2.47%, indicating that introducing the GO-COOH thin film as a hole transport layer can effectively improve energy-transfer efficiency of the device.2. Respectively using ammonia water, ethylene diamine and diethylene triamine as a source of ammonia, citric acid as a carbon source, we prepared amino graphene quantum dots(named as N1-GQDs, N2-GQDs, N3-GQDs). Photoluminescence experiment shows that the dimensions of the three quantum dots are gradually decreases. IR, UV and fluorescence spectroscopic described its optical properties. Then use these N-GQDs as a hole transport layer for P3HT: PC61 BM battery device, look forward to researching the affection of the N-GQDs concentration, spin speed and UV ozone cleaning process(UVO) and other factors on device performance. The following conclusions:1) N1-GQDs played almost no role in the electric transportation, because its size is too large and hindered the transport of electric, leading that the device is little efficient. While the N2-GQDs and N3-GQDs as an electric transport layer, various performance parameters of the device have been enhanced, PCE reached 2.66% and 3.42%, indicating that the smaller the size of the material, the distribution of the average photoelectric conversion efficiency more high.2) Use N3-GQDs for the study object, optimize the concentration of N3-GQDs and the rate of spin coating, and the results showed that the concentration of N3-GQDs at 0.6 mg/m L is most appropriate, the best spin coating rate is 4500 rpm. While the concentration is small or spin coating at a faster rate, N3-GQDs film thickness is getting smaller, does not bring the ITO surface is completely covered. Due to the greater energy level does not match the contact barrier, resulting lower Jsc and FF and efficiency of device. But when N-GQDs concentration is too large or spin coating rate is slow, N-GQDs film thickness increases, resulting in an increase in the series resistance of the device, the Jsc and FF of device decrease, thus the efficiency of the device is reduced.3) After the ITO glass with UVO treatment, device performance becomes excellent. Which is due after UVO treatment, the surface of ITO can be removed in the small amount of residual contaminants, and it also can increase the N-GQDs' wettability on ITO surface, and can improve the work function of ITO, leading more energy level matching, electron transport easier, JSC has been greatly improved, so the device performance has been improved.