Study On Organic Solar Cells With Novel Donor Polymers And Dopant Controlling For Active Layers

Polymer solar cells were firstly studied in1970s. They have attracted muchscientists’ attention recently because of their advantages of light-weight, solubleprocessing and large-scale and flexible fabrication. This thesis studied that somenew conjugated polymers were used in polymer solar cells as donors. Then theeffect of the doping materials in active layers by the electric controlling on theperformance of solar cells was also researched. The main contents of this paperinclude:(1) Polymer solar cells with six novel conjugated polymers as donors werestudied. By measure of CV and UV-Vis spectrum, we analyzed their opticalperformances. SEM was employed to analysis their inter-solubility withacceptors. One of these materials has a band-gap of about1.5eV, which is smallerthan the other materials. It also has better absorption ability to solar light. Afteroptimizing the film thickness, the solar cells based with these materials have thehighest efficiency of2.14%combining with larger open voltage. Theperformance is much better than that of the other materials as donors. As shownin SEM pictures, good mixture is formed between acceptor PCBM and the donorpolymers.(2) Polymer solar cells with optimized active layers of P3HT: PCBM wereresearched. The solar cells with active layers from slow grown crystallization hadthe highest efficiency of3.9%, short current density of10.1mA/cm~2and aboutEQE of60%. But for active layers from fast grown crystallization had a lowerefficiency of2.7%, short current of9.5mA/cm~2and about EQE of45%. The Vocof these cells had a same level. The surface of slow grown crystallizated film ismore rough than that of the fast grown crystallizated film. Some particlesaggregated together, which made the cathode contacted more tightly with theactive layer and provided more interface for excitons to separate. Furthermore bydoping the active layers of P3HT: PCBM with organic material TAZQ, thetransmission ability of electrons in active layer was improved. In the range of theweight ratios of0.1%、1%and0.5%, the PCE、Jsc、EQE increase with theincrease of the weight ratio.(3) Polymer solar cells with two PCBM derivates as acceptors were alsocharacterized. By adding Br element and nitrogen element to the C60balls. Thetwo kinds of acceptors have near energy level with PCBM. By analyzing thepicture of optical probe and SEM, the two kinds of acceptors had poor dissolvingability, and there is obvious crystallization on the surface of active layer. According to the date tested from the solar cells, although the mixture of the twodonors is enough to the acceptors, the performances of the solar cells are stillpoor. However, they show the better absorption ability of solar energy.(4) Polymer solar cells with the active layers doped with organic salt inwhich the onions and cations were vertically separated under the high electricfields. The onions gather on one side of the active layer, forming a dipole withcations, which will improve the transmission of the electrons and collectionability of cations. This result is also proved by EDS measurement. It also workswell on the preliminary step of the experiment. But further experiment provesthat it is wrong to select this kind of organic salt since it wasn’t dissolved into theactive layer of P3HT: PCBM.