图4 申请人课题组最近开发的BTP-Se的分子结构、形貌和光伏性能表征
为了解决上述一些问题,申请人课题组近期在不对称Y系列FREAs的结构修饰方面开展了一些工作。首先在Y6分子的稠环中心核和2FIC端基之间插入不同数量(1~4)的乙烯基π桥,得到一系列乙烯基π桥修饰的超窄带隙Y系列FREAs。随插入π桥数量的增加,它们的HOMO能级逐渐的提升而最低未占有分子轨道(LUMO)能级只有略微的下降,Egopt显著减小;当只插入一个乙烯基π桥得到的不对称FREA分子BTP-1V-2F,HOMO和LUMO能级比Y6略微上升,但是其吸光范围拓宽了52 nm,与PM6共混制备的单结二元器件获得14.24%的效率,这也是基于超窄带隙(Egopt ≤1.29 eV)FREA的单结二元OSCs最高效率之一[24];在此基础上我们还采用杂稠环策略,将中心缺电子核的苯并噻二唑替换成苯并硒二唑单元,合成一种新的FREA分子BTP-Se(结构如图2所示),其紫外-可见-近红外光谱吸光边缘拓宽至1000 nm,Egopt降低至1.24 eV,当其与PBDB-T共混制备二元器件,PCE为14.2%,这是基于PBDB-T二元器件的最高值之一,其器件的Jsc达到28.66 mA cm-2,这是所有单结二元OSCs最高值[25]。申请人通过梳理文献发现,报道超高Jsc值基本都是通过三元共混或者叠层器件实现[26-28],如果能通过分子工程对BTP-Se分子的π桥进一步优化结构,保持超高Jsc的同时有效提升开路电压和填充因子,采用聚合化FREA策略应用于all-OSCs,其器件效率还有很大的提升潜力。
本项目针对缺乏高性能poly-FREA受体材料问题,申请人拟对课题组前期开发的FREA分子BTP-Se开展多层次分子工程:不对称结构中π桥单元的替换,引入单溴取代氰基茚酮端基,与不同单元聚合化FREA,最终获得一系列具有超高短路电流的聚合物受体材料。通过调控分子结晶性、能级、吸光和均衡电荷传输性能,筛选和高性能聚合物给体材料(PM6、D18和PBDB-T)匹配的poly-FREA,制备二元电池并优化,实现超高电流密度效率18%以上的all-OSCs。本项目全面考察不对称π桥单元对poly-FREA吸收光谱、能级、固相聚集性能的调控,揭示受体材料分子结构对活性层的载流子迁移率、相分离形貌和光伏性能的影响规律;研究其与聚合物給体配伍因素,结合器件工程探究电池器件能量损失机制。本项目深化分子工程提高光伏性能的研究理念,对探索解决高效率全聚合物太阳能电池的关键科学问题和推动全聚合物太阳能电池应用研究具有重要意义。
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