| With development of pulsed laser technology, the technology of transient absorption spectrum has made great headway. It be mainly used to measure the property of transient materials(excited state, free radical,and so on) generated by laser excitation, so it has been widely used in chemical and physical area. Solar energy as a clean, renewable energy has been widely attention. Organic solar cells because of its low cost, light weight, flexibility etc, has become a hot research topic in the field of solar energy application. For organic solar cells, however, due to the influence of some factors, such as the generation, diffusion, composite of exciton and carrier collection of electrode, the solar energy conversion efficiency(PCE) of organic solar cells compared with that of traditional inorganic solar energy conversion efficiency(PCE) is low. This has become the important hindrance in large-scale commercial production of polymer solar cells. Therefore, how to improve the photoelectric conversion efficiency of organic solar cells has been becoming the current hot research topic. In this paper, we will use femtosecond transient time resolution absorption spectrum to study the formation of polaron and influence of inhibitors of fluorescence in the blend film of 3- hexyl thiophene: fullerenes(P3HT: PCBM).Firstly, the film has been fabricated based on poly(3-hexylthiophene)(P3HT) as electron donors in organic solvents. The femtosecond transient time resolution spectrum has be used to test the film. The result shows that when P3 HT absorb pump light(400nm) the singlet state excitons located in the S4 excited state will be generated, and the lifetime of the excitons is T=2652.4fs. At the same time, the lifetime of excitonic decay trough radiative transition(thermal relaxation) and non-radiative transition(fluorescence) back to the ground state is T=4394.89 fs.Secondly, the process of exciton dissociation and polaron formation in P3HT/PCBM blend film has been studied. The result indicates that the decay process of exciton will be increased due to formation of CT(charge transfer) state when PCBM is added in P3HT(the fast decay process T=632.8fs), and there are three phases in P3HT:PCBM blend films: fibrillar network of PCBM crystals, aggregates of PCBM nanocrystal, and relatively disordered P3 HT matrices with PCBM nanocrystal. Due to this morphology of the blend film, the polaron formation process can be divided into fast process(877.6fs) and slow process(124661 fs). On the one hand, the exciton generated when the disordered P3 HT are excited by photon don’t need to diffuse and can be dissociated directly at the donor/acceptor interface. On the other hand, Donor absorbs light in P3 HT crystals and generates exciton, It is essential that this exciton diffuses to the interface of donor and acceptor for dissociation.At the end of this thesis, femtoseconed transient time resolution absorption spectrum has be used to study effects of doping fluorescence inhibitors(1-Bromo-4-Nitrobenzene) in the blend film using poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl C60-butyric acid methyl eater(PC60BM) as donor and acceptor respectively. The Result indicates that the intensity of fluorescents of blend film can be inhibited when 1-Bromo-4-Nitrobenzene be used as Fluorescent inhibitors. Trough compared with undoped cell, the time of single exciton injected into CT state and dissociated as polaron(P3HT+ and PCBM-) in cell doping nitrobenzene are less than that in undoped cell(T(time of exciton injection) decreases from 632.8fs to 543.2fs; T(time of exciton dissociation) decreases from 877.6fs to 743.1fs). So more excitons can be dissociated. |
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