Preparation And Optoelectronic Properties Of Fused Fluorene Conjugated Polymeric Materials

In the last decade, organic photovoltaic (OPV) technology has beendeveloped from less than1%power conversion efficiency (PCE) to about10%due to the depth understanding of the materials and device structure. Comparedwith the conventional inorganic semiconductor solar cells, organic solar cellsoffer magnetic advantages including simple preparation, production of low cost,light weight and large area processing for flexible devices. However, to date, thepower conversion efficiency in turning light into electricity is still not responsiblefor commercial requirements. The reasonable molecular design and synthesis ofthe high-performance photovoltaic materials is one of the main routes to improvethe power conversion efficiency. Utilizing advantages of easily modification andcutting in the chemical structure for organic molecules, herein, we designed andsynthesized a series of fluorene-based polycyclic two-dimensional conjugatedpolymer donor materials with large π-conjugated structure, and exploited theirintrinsic structure-property relationship, providing guidance and reference forfuture design and exploration of high-performance photovoltaic materials. Themain contents are as follows:1. Six donor-acceptor type conjugated polymer donors with two-dimensionalconjugated structure were prepared via Stille copolymerization of a new buildingblock of dithieno[6,5-b:10,11-b’]-8H-cyclopentyl[1,2-b:4,3-b’]diphenanthrene aselectron-donating monomer and six different electron-deficient units. All thepolymers show good solubility in common solvents and thermal stability withthermal decomposition temperature of5%weight loss above330℃. The opticalband gaps(Egopt) of these polymers are located from1.65eV to1.93eV. Thehighest occupied molecular orbital (HOMO) energy levels are located from-5.4eV to-5.13eV, so that the lowest unoccupied molecular orbital (LUMO) energylevels are located from-3.59eV to-3.28eV.2. A new building block of monomer13was designed and synthesized, andincorporated as donor unit to construct a new D-A type conjugated polymer P7. Polymer P7has good thermal stability with thermal decomposition temperature ofat323℃. The optical band gap (Egopt) of the polymer is1.95eV. The highestoccupied molecular orbital (HOMO) energy level is-5.34eV and the lowestunoccupied molecular orbital (LUMO) energy level is-3.39eV, which arecompatible with those of PC61BM. Compared with the polymer P3, polymer P7has stronger aggregation because of stronger interaction between molecules,which facilitate charge transport. The lower HOMO energy level is morefavorable for improving the open circuit voltage of the device.