Conjugated Organic Electron Transporting Layer And Its Application In Organic Solar Cells

As one of the emerging energy sources,organic solar cells have become a research hotspot because of their low cost,low pollution,light weight and flexibility.However,due to low efficiency and poor stability,the commercial application was restricted.There are many ways to improve device efficiency,such as the development of new donors,acceptor materials,solar cell procedure optimization,and interface modification.At present,the electron transport layers used in organic solar cells are generally inorganic metal oxide such as ZnO and Cs₂CO₃.These inorganic layers have high conductivity and strong electron transporting ability,but since the active layer is an organic materals,ohmic contact between ZnO and the active layer is poor.Therefore,in this paper,we introduced a conjugated organic compound as electron transport layer in organic solar cell.Compared with inorganic cathode intercalation layer,the organic electron transport layer has good solubility in the polar solvent,and easier to be frabicated in the lab and factory.Besides,a variety of organic materials can be obtained by introducing different groups to avoide the unity of the inorganic material.This paper was mainly including the following contents:1.Two different molecular weight pyrrolopyrrolediones copolymerization fluorene derivatives（PDTFN-L and PDTFN-H）were synthesized by the Suzuki-Miyaura reaction.We dissolved the polymer with active layer,which can replace the role of the electron transport layer,but does not require additional spin coating of the electron transport layer,simplifying the operating procedure and reducing the cost of the cell preparation process.Since the alkyl group in the polymer molecule ensured good contact with the active layer,and the nitrogen atom in the polymer interacts with the oxygen atom of the ITO,the work function of the ITO was significantly reduced,which can greatly promote the built-in electric field and increased the open circuit voltage.Even when the active layer containing 0.5 mg of PDTFN-H and extraly coating the ZnO electron transport layer,the efficiency was higher than that of the cells with ZnO transport layer and the efficiency was 2.93%.More importantly,we removed the ZnO electron transport layer and found that the solar cell was more efficient,reaching3.62%.2.Three kinds of perylene diimide derivatives（PDIH,PDIC and PDIN）with different side chain modifications were synthesized mainly by the substitution reaction of dibromophthalimide derivatives and different phenol derivatives.The PDIH and PDIC were constructed into solar cells without electron transport layer,and the efficiency was found to be lower than that of ZnO.The active layer was found to be rougher.And the work function of ITO was not significantly reduced,which tested by UV photoelectron spectroscopy.While PDIN replaced ZnO as the organic electron transport layer.Under the synergistic effect of improving the hole transporting efficiency and reducing the work function of ITO to 4.05eV,the cell efficiency can reach 3.12%.3.In the last system,biphenyldiimide and naphthalene diimide derivatives（LBI-S,NDI-S,DA-LBI and DA-NDI）were synthesized and could dissolve in a polar solvent such as methanol or water and was insoluble in chlorobenzene,which can effectively prevent the erosion from active layer solution.The solar cell efficiency of LBI-S and NDI-S linked to sulfobetaine were lower than that of methacrylic anhydride DA-LBI and DA-NDI,mainly because the latter can smoother the active layer.After the ultraviolet light treatment,DA-LBI and DA-NDI can undergo a crosslinking reaction to form a polymer.In addition,DA-LBI and DA-NDI can reduce the ITO work function to a greater extent,enhancing a larger built-in field,and correspondingly higher open circuit voltage.