Ternary Bulk Heterojunction Solar Cells And Exciton Separation Efficiency

In order to broaden the scope of organic polymer solar cells on the absorption of the solar spectrum, the thesis first explores the doping low band gap polymer PCPDTBT on ternary cell P3HT:PCPDTBT:ICBA performance impact, after changing the doping ratio, annealing conditions, the chemical additive (1,8-octanedithiol) used, the study found that the short-circuit current density(Jsc) would be reduced after doping PCPDTBT compared to P3HT:ICBA device, and the reduction was increases with increasing doping concentration of PCPDTBT.Based on the above research, the thesis studies the calculation exciton separation efficiency of organic solar cells, with the use of donor and acceptor materials’ absorption spectrum, emission spectrum to calculate the exciton separation efficiency, the method introduced in the thesis is simple and easy implementation, the study can provide the basis for materials selection when diffenent donor and acceptor materials are chosen to made the bulk heterojunction solar cells. At the same time, the exciton separation efficiency calculated by this method between the PCPDTBT and ICBA is low, only12%, it affects the production of free carrier in ternary battery device and the short circuit current density, in turn, the performance of the devices is low.In the thesis,differnet devices based on different donors (P3HT, PCPDTBT) and acceptors (PCBM, ICBA, F8BT) matching are prepared inorder to explore the exciton transfer state between donor and acceptor by calculating the exciton separation efficiency. Each donor’s exciton separation efficiency in the structures of P3HT:PCBM and PCPDTBT:PCBM is around70%by studied, while the exciton separation efficiency in the system of PCPDTBT:ICBA12%.The results well explain the variation of Jsc in different D/A structures. Further analysis of the energy level diagram of D/A system, it found that the difference of LUMO energy level of donor and acceptor will affect the exciton separation efficiency. For P3HT:F8BT device, the reason of the low Jsc is that there is energy transfer process from F8BT to P3HT so as to the PL increasing of P3HT and the generation of new exciton in P3HT, this inhibits the effective separation of the excitons and will affect the Jsc of devices.