Nitrogen-Containing Aromatic Heterocycles Based Narrow Band-Gap Donor Polymers And Bulk-hetcrojunction Solar Cells

Polymer solar cells(PSCs), as one kind of novel solar cells, are becoming increasinglymore and more attractive academically and industrially, because of its versatile merits in lightweight, cheap price, feasible fabrication, large-scale area and easy structure tuning. In theresearch field of PSCs, the preparation of low band-gap donor materials is the important issue.As an ideal donor material, it must exist broad solar absorption, high short current density,high open circuit voltage and high fill factor.Therefore, in this dissertation, we designed and synthesized novel D-A narrow band-gappolymers; and through the fine tuning by the different substituted groups, the polymers withdifferent HOMO energy levels were obtained, which can tune the open circuit voltage inPSCs feasibly.Preliminarily, an octyloxy substituted benzofunazan derivative was synthesized. Thisderivative had good solubility in common organic solvents, which was beneficial forenhancing the polymers’ solubility in polymerization and acquiring the narrow band-gappolymers with high molecular weight. Moreover, it had good planarity which can increasepolymrs’ solar absorption. Through the polymerization between this derivative and carbazole,indocarbazole or thiophene, a series of narrow band-gap polymers based on octyloxysubstituted benzofunazan were synthesized. In these polymers, the one containing octyloxysubstituted benzofunazan derivative and carbazole had the best photovoltaic performance withthe power conversion efficiency of5.48%.Furthermore, a series of different groups substituted triphenylamine based narrowband-gap polymers were designed and synthesized. Through the decoration by theelectron-donating alkyl and alkoxy groups, and electron-withdrawing trifluoromethyl groupsin triphenylamine, the HOMO energy levels of target polymers could be adjusted feasibly, andultimately the open circuit voltages in these PSCs were tuned. The electorn-donating alkyland alkoxy groups in triphenylamine can increase the HOMO energy level and decrease theopen circuit voltage in PSCs; on the other hand, the electron-withdrawing trifluoromethlygroups could decrease the HOMO energy level and increase the open circuit voltage. Finally,the open circuit voltages in PSCs based on these narrow band-gap polymers can be tuned between0.70V and1.00V.At last, two fluorene-derivatives based polymers, which were substituted by the C=Ndouble bonds in9-position, were designed and prepared. Through the substitution in9-position by the C=N double bonds, it can increase the molecular planarity which wasbeneficial for enhancing the π-π stacking between the polymer main chains. On the other side,the electron-withdrawing C=N double bonds can decrease the polymers’ band gap whichwould increase the polymers’ solar absorpation. The photovoltaic properties based on thesepolyfluorenes can reach to the power conversion efficiency of about0.5%.