Vertebrate poxviruses encode homologs of cellular cupro-zinc superoxide dismutases (Cu-Zn SOD). In this study we have examined the molecular genetic properties of two Cu-Zn SOD homologs encoded by the Shope fibroma virus (SFV) and myxoma virus. These Leporipoxvirus proteins should be catalytically inactive as judged by the point mutations which alter a key catalytic arginine and restructure the predicted Cu-binding domain. This prediction was confirmed using in situ gel assays and recombinant proteins produced both in bacteria and in mammalian cells. Western blot analysis showed that these proteins are produced in abundance late in infection and can, upon exposure to oxidizing conditions, form disulfide cross-linked dimers. They are also virion components and not essential for growth in culture or virulence. Leporipoxvirus Cu-Zn SOD homologs affected two phenotypes. First, deletion of the myxoma M131R gene caused the mutant virus to grow better ( approximately 10-fold) in culture than does the wild-type parent. Second, expression of either native or recombinant Leporipoxvirus proteins is accompanied by a decline in cellular Cu-Zn SOD activity. We concluded that these gene products can somehow modulate the activity of host Cu-Zn SODs, but what advantage is thus gained by the virus remains to be established.
The introduction of fluorine (F) atoms onto conjugated polymer backbone has verified to be an effective way to enhance the overall performance of polymer-based bulk-heterojunction (BHJ) solar cells, but the underlying working principles are not yet fully uncovered. As our attempt to further understand the impact of F, herein we have reported two novel fluorinated analogues of PCDTBT, namely, PCDTFBT (1F) and PCDT2FBT (2F), through inclusion of either one or two F atoms into the benzothiadiazole (BT) unit of the polymer backbone and the characterization of their physical properties, especially their performance in solar cells. Together with a profound effect of fluorination on the optical property, nature of charge transport, and molecular organization, F atoms are effective in lowering both the HOMO and LUMO levels of the polymers without a large change in the energy bandgaps. PCDTFBT-based BHJ solar cell shows a power conversion efficiency (PCE) of 3.96 % with high open-circuit voltage (VOC) of 0.95 V, mainly due to the deep HOMO level (-5.54 eV). To the best of our knowledge, the resulting VOC is comparable to the record VOC values in single junction devices. Furthermore, to our delight, the best PCDTFBT-based device, prepared using 2 % v/v diphenyl ether (DPE) additive, reaches the PCE of 4.29 %. On the other hand, doubly-fluorinated polymer PCDT2FBT shows the only moderate PCE of 2.07 % with a decrease in VOC (0.88 V), in spite of the further lowering of the HOMO level (-5.67 eV) with raising the number of F atoms. Thus, our results highlight that an improvement in efficiency by tuning the energy levels of the polymers by means of molecular design can be expected only if their truly optimized morphologies with fullerene in BHJ systems are materialized.
Two small molecule donor materials (DTGe(FBTTh2)2 and DTGe(FBTBFu)2) incorporating the dithienogermole (DTGe) moiety with fluorobenzothiadiazole (FBT) and bithiophene (Th2) or benzofuran (BFu) end‐capping groups are synthesized and their properties as donor materials in small molecule bulk heterojunction type (BHJ) solar cells are investigated. The DTGe(FBTTh2)2 with Th2 end groups shows outstanding solar cell characteristics with efficiencies up to 6.4% using a standard BHJ architecture and 7.3% using a ZnO optical spacer, while the BFu end‐capped DTGe(FBTBFu)2 has slightly wider band gaps and yields slightly higher open circuit voltage (VOC) at the expense of short circuit current (JSC) and fill factor (FF). In this study, the DTGe‐based molecules are systematically compared to the dithienosilole (DTSi)‐based analogues, which are currently among the highest power conversion efficiency (PCE) small molecule solar cell donor materials known. The JSC produced by the DTGe molecule is found to be similar to, or slightly higher than the Si analogue, despite similar absorption characteristics, however, the PCE is similar to the Si analogues due to small decreases in VOC and FF. This report marks the first small molecule BHJ based on a Ge‐containing heterocycle with PCE over 7%.
The synthesis and characterization of two new small molecular donor materials, DTGe(ThFBTTh) and DTGe(FBTTh), are presented for application in organic solar cells. These two materials represent structural evolutions of the high-efficiency, dithienogermole (DTGe)-cored small molecule DTGe(FBTTh), in which the conjugation length in the backbone was extended by incorporating additional thiophene units. Using the same molecular framework, we have evaluated how the anchoring sequence of heterocyclic units influences material properties and function in solar cell devices. It was found that incorporating additional thiophene units into the backbone, regardless of the position in the molecular platform, caused a small reduction in band gaps; however, both highest occupied molecular orbitals and lowest unoccupied molecular orbital energy bands were at lower energies when the thiophenes were incorporated near the terminus of the molecule. The film morphologies of both materials could be controlled by either thermal or solvent vapor annealing to yield phase separation on the order of tens of nanometers and improved crystallinity. Peak power-conversion efficiencies of 3.6% and 3.1% were obtained using DTGe(ThFBTTh) and DTGe(FBTTh), after solvent vapor treatment and thermal annealing, respectively. Our study provides a detailed analysis of how the ordering sequence of heterocyclic building blocks influences the properties and function of organic solar cells.
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