The Study Of Organic Solar Cells Incorporating Polyfluorene Polymers

Compared with the traditional inorganic solar cells, organic solar cells(OSCs)possessing the advantages of low cost, wide material source, mechanical flexibility and large-scale manufacturing, have been widely concerned by domestic and foreign researchers. However, the insufficient photoelectric conversion efficiency limits their application and promotion, which mainly attributes to two problems; one is lower spectrum utilization due to the low absorbance of devices, the other is the hampered charge transport due to the unmatched energy structure. Thus, it is a crucial issue to improve the property of devices by broadening the absorption of active layer and promoting the transport of charge carriers.To settle above problems, some methods have been studied, such as synthesizing narrow band gap polymer and fabricating cascade solar cells and so on. Though these methods could efficiently solve problems of low light absorption and bad charge transport,some negative factors restrict their development, such as long preparation cycle and complex experiment process. In this work, we doped some materials into active layer or cathode buffer layer. Doping is a simple, easy and well-effect way to improve the devices property. We employed Polyfluorene(PF) and its derivatives possessing the advantage of photoluminescence effect and easy modification. We fabricated the inverted polymer solar cells with the structure of ITO/Ti O2/PCDTBT: PCBM:PFDTBT/Mo O3/Ag. Now, increased light absorption and charge transport property lead to higher short-circuit current density(Jsc) and fill factor(FF) and some improvement of film morphology, resulting in a higher efficiency approaching to 7%, which achieves a breakthrough in device performance.Meanwhile, we also doped three kinds of PF materials into polyethylenimine(PEI)cathode buffer layer respectively, fabricating the cell devices with the structure of ITO/PEI:PF/P3HT:PCBM/Mo O3/Ag. These three kinds of PF could effectively convert the ultraviolet light into visible light, further being used by active layer. Thus, PF doped intobuffer layer could enhance light absorption and utilization of active layer. At the same time,PF demonstrates high carrier mobility, which contributes to the enhancement of the charge transport. After a series of optimization process, the power convert efficient(PCE) of devices based on the P3HT:PCBM was increased from 3.52% to 4.72%.In this paper, we doped PF and its derivatives into active layer and cathode buffer layer respectively, which contribute to the increased light absorption and the enhanced charge transport, leading to an improvement of the devices efficiency. Device fabrication,measurement and characterization are detailedly described, which provides good approach to the exploration and research of the cells.