Synthesis And Applications Of DPP-based Molecular Photovoltaic Materials

In recent years,organic solar cells have been a hot topic due to its advantage of light weight,low cost,flexibility and solution-processable capabilities.The design and synthesis of non-fullerene acceptors and molecular donors is very effective in improving the photovoltaic properties of the organic solar cells and now is a research hotspot in this field.Accordingly,our main work is as followed.1.A non-fullerene electron acceptor with a spirobifluorene（SF）core and four diketopyrrolopyrrole（DPP）arms end capped by 4-fluorobenzene（FB）,is designed and synthesized.Comparing to its non-fluorination analogue,the introduction of fluorine reduces the lowest unoccupied molecular orbital（LUMO）energy levels of SF（DPPFB）4 and improves the electron mobility of the poly（3-hexylthiophene）（P3HT）and SF（DPPFB）4 blends.The highest power conversion efficiency obtained by the OSCs based on P3HT:SF（DPPFB）4 is 4.42%,with a lifted short current density of 8.48 mA cm-2.2.An organic small molecule with a fluorene（F）core and two diketopyrrolopyrrole（DPP）arms end capped by ethyl thiophene-2-carboxylate（CT）,F（DPPCT）2,which can serve as both the acceptor and the donor,is designed and synthesized.The optical energy gap is 1.65 eV,with a LUMO of-3.68 eV and HOMO of-5.28 eV.The resulting devices based on P3HT:F（DPPCT）2 and F（DPPCT）2:PC7iBM can give a highest power conversion efficiency of 2.14%and 2.50%,respectively.3.An organic molecular donor with a benzodithiophene（BDT）core and two diketopyrrolopyrrole（DPP）arms end capped by ethyl thiophene-2-carboxylate（CT）,BDT（DPPCT）2,is designed and synthesized.It shows intense absorptions in the range of 500 nm-800 nm.The optical energy gap is 1.54 eV,with a LUMO of-3.40 eV and HOMO of-5.03 eV,suggesting a typical p type semiconductor.From the 1H NMR spectrum,we know that BDT（DPPCT）2 is strongly aggregated and π-π stacked even in solution,which contributes to high electron mobility.However,BDT（DPPCT）2 is too aggregated to be soluble in the hot solutions of common solvents,and we can’t get a uniform film with the hot-spin-coating method.The resulting device based on BDT（DPPCT）₂:PC₇₁BM can give a highest power conversion efficiency of only 0.835%.