Porphyrins/Phthalocyanines Cathode-lnterlayer Materials And Their Applications In Organic Solar Cells

In recent years, the power conversion efficiency (PCE) of organic solar cells(OSCs) higher than10%has been achieved with rapid development. To improvethe PCE of PSCs, great deal of progress has been made in the synthesis of newmaterials, device structure optimization and interface technology. Moreover, theinterface of an electrode and an active layer has well attracted increased attentionto improve device efficiency by minimizing charge collection/extraction barriersand forming ohmic contact between an electrode and an active layer. Manymaterials such as LiF, metal oxides, alcohol/water soluble polymer and organicsmall molecules used as cathode interlayers have successfully enhanced the PCEof OSCs. Compared to other cathode interfacial layer materials, advantages ofalcohol/water-soluble polymeric or organic materials are apparent in the OSCsdue to their simple and vacuum-free procedure to form film during the devicefabrication. In my doctoral thesis, we have synthesized a series ofporphyrin/phthalocyanine derivatives and studied their physical and chemicalproperties. Then the porphyrin/phthalocyanine derivatives were employed ascathode interlayers to fabricate OSCs.1. In chapter II, we have synthesized three ionic porphyrin derivatives: Zn-TPyPMeI, Zn-TPyPAdBr and MnCl-TPyPAdBr. They were employed ascathode interlayers to fabricate OSCs by spin-casting method. The PCDTBT andPC71BM blend films were used as active layers. The OSCs with porphyrinscathode interlayers showed obviously higher short circuit current (Jsc), opencircuit voltage (Voc), the fill factor (FF) and PCE than those without interlayers.The highest PCE,6.86%, was achieved for the device with MnCl-TPyPAdBr asan interlayer. The photovoltaic performance of the cathode interfacial layermaterials has been controlled by changing the outside functional groups andcenter coordination metals of H2-TPyP, which provides useful information forpreparation of more excellent cathode-interlayer materials.2. In chapter III, the group of2-(dimethylamino) ethanethiol had substitutedeight β positions of zinc phthalocyanine and then methylation reaction wasemployed to afford ZnPc[S(CH2)2N(CH3)3I]8. ZnPc[S(CH2)2N(CH3)3I]8wasemployed as cathode interlayer to fabricate OSCs by spin-casting method. ThePCDTBT and PC71BM blend films were used as active layers. The OSCs withcathode-interlayer material ZnPc[S(CH2)2N(CH3)3I]8showed obviously higherJsc, Voc, FF and PCE than those without interlayers. The PCE has furtherincreased to7.06%.3. In chapter IV, we have synthesized three ionic phthalocyanine derivatives:VOPc(OPyC2H5Br)8, VOPc(OPyC4H9Br)8and VOPc(OPyC6H13Br)8bychanging the alkyl chains attached to the pyridine functional groups of2,3,9,10,16,17,23,24-octakis (3-pyridyloxy) vanadylphthalocyanine (VOPc(OPy)8). They were employed as cathode interlayers to fabricate OSCs byspin-casting method. The PTB7and PC71BM blend films were used as activelayers. In this chapter, we have utilized simple organic synthesis to change the alkyl chains attached to the pyridine functional groups of VOPc(OPy)8.Increasing the alkyl chains not only weaken intermolecular interactions, but alsopromote the wettability of the cathode interfacial material on the surface of theactive layer. It provides helpful information for the development of highperformance and high-quality-film cathode interfacial materials4. In chapter V, we have synthesized three alcohol soluble phthalocyaninederivatives: ZnPc(OC4H9OPyCH3I)8, ZnPc(OC6H13OPyCH3I)8and ZnPc(OC8H17OPyCH3I)8by adding different alkoxy chains to eight positions of2,3,9,10,16,17,23,24-octakis-[N-methyl-(3-pyridyloxy)] zincylphthalocyanineiodide (1:8)(ZnPc(OPyCH3I)8). They were employed as cathode interlayers tofabricate OSCs by spin-casting method. The PTB7and PC71BM blend filmswere used as active layers. The highest PCE,8.73%, was achieved for the devicewith ZnPc(OC4H9OPyCH3I)8as an interlayer. Because phthalocyanine moleculehas a very large π-conjugated system, it is very easy to assemble, which leads toa coarse film. Therefore, such a chemical modification provides the moleculewith an ideal balance between the solubility and intermolecular π-π stacking byadding different alkoxy chains to eight positions of ZnPc(OPyCH3I)8. The highconformational flexibility of the alkoxy chains affords phthalocyaninederivatives sufficient solubility in methanol, which promotes the wettability ofthe cathode interfacial materials on the surface of the active layer. Weakerintermolecular π-π stacking in the phthalocyanine derivatives during the filmformation realizes the uniform deposition on the lying organic layer. Atomicforce microscopy (AFM), contact angle characterizations and othermeasurements were used to study the morphology of the cathode interlayer. Thephthalocyanine derivatives were also introduced into the OSCs based on different active layers to demonstrate their universality acting as cathodeinterlayers. It is worth noting that ZnPc(OC8H17OPyCH3I)8has very goodsolubility in ethanol. The ZnPc(OC8H17OPyCH3I)8film as a CIL prepared fromethanol solution can also remarkably enhance OSCs performance. These resultssuggest a possible approach to fabricate high-performance OSCs with greenersolvents. It provides helpful information for the development of highperformance and environment-friendly cathode interfacial materials.