Jiang Haiying, Pan Feilong, Zhang Lianjie, Zhou Xiaobo, Wang Zhen, Nian Yaowen, Liu Cang, Tang Wei, Ma Qiao, Ni Zhenyu, Chen Mingjun, Ma Wei, Cao Yong, Chen Junwu
Institute of Polymer Optoelectronic Materials & Devices, State Key Laboratory of Luminescent Materials & Devices , South China University of Technology , Guangzhou 510640 , P. R. China.
State Key Laboratory for Mechanical Behavior of Materials , Xi'an Jiaotong University , Xi'an 710049 , P. R. China.
ACS Appl Mater Interfaces. 2019 Aug 14;11(32):29094-29104. doi: 10.1021/acsami.9b08722. Epub 2019 Aug 2.
To thoroughly disclose the role of the siloxane-terminated side chain with different substituent positions, three difluorobenzotriazole-dithienylbenzodithiophene (FTAZ-BDTT)-based polymers PBZ-1Si, PBZ-2Si, and PBZ-3Si with the siloxane-terminated side chain on the FTAZ unit (PBZ-1Si), on the BDTT unit (PBZ-2Si), and both on BDTT and FTAZ units (PBZ-3Si), respectively, were synthesized. The different side chain substitutions have slight influences on absorption behavior, thermal stability, and frontier molecular orbitals but have shown a great effect on the aggregation of the polymers. Grazing-incidence wide-angle X-ray scattering measurements reveal that, relative to PBZ-1Si with branched alkyl on the BDTT unit, polymers PBZ-2Si and PBZ-3Si, bearing the siloxane-terminated side chains on the BDTT unit, exhibit smaller π-π stacking distances and larger crystal coherence lengths, suggesting that adopting the siloxane-terminated side chain on the BDTT unit can promote the interchain π-π interaction and the ordering of molecular packing. With IT-M as the non-fullerene acceptor, among the three polymers, the PBZ-2Si-based active layer possesses the highest ordered crystals for both polymers and IT-M as well as the purest domain, which affords efficient exciton dissociation, the most balanced hole-electron transport, and reduced recombination, leading to the highest short-circuit current density () and fill factor (FF) and then the highest power conversion efficiency (PCE) of 11.14%. In contrast, PBZ-1Si- and PBZ-3Si-based devices show lower PCEs of 8.98 and 9.92%, respectively. Moreover, PBZ-2Si:IT-M also exhibits good thickness tolerance, and its thick active layer of 240 nm shows the most limited decrease of efficiency after 77 days of storage, supplying good potential for mass fabrication. Our work suggests that the fine pairing of a siloxane-terminated side chain and an alkyl side chain is beneficial for the optimizing of a conjugated polymer donor toward high-performance non-fullerene polymer solar cells.
为了全面揭示不同取代位置的硅氧烷封端侧链的作用，分别合成了三种基于二氟苯并三唑-二噻吩基苯并二噻吩（FTAZ-BDTT）的聚合物PBZ-1Si、PBZ-2Si和PBZ-3Si，其硅氧烷封端侧链分别位于FTAZ单元（PBZ-1Si）、BDTT单元（PBZ-2Si）以及BDTT和FTAZ单元上（PBZ-3Si）。不同的侧链取代对吸收行为、热稳定性和前沿分子轨道有轻微影响，但对聚合物的聚集有很大影响。掠入射广角X射线散射测量表明，相对于BDTT单元带有支链烷基的PBZ-1Si，BDTT单元带有硅氧烷封端侧链的聚合物PBZ-2Si和PBZ-3Si表现出更小的π-π堆积距离和更大的晶体相干长度，这表明在BDTT单元上采用硅氧烷封端侧链可以促进链间π-π相互作用和分子堆积的有序性。以IT-M作为非富勒烯受体，在这三种聚合物中，基于PBZ-2Si的活性层对于聚合物和IT-M都具有最高的有序晶体以及最纯净的区域，这实现了高效的激子解离、最平衡的空穴-电子传输以及减少的复合，从而导致最高的短路电流密度（）和填充因子（FF），进而实现了11.14%的最高功率转换效率（PCE）。相比之下，基于PBZ-1Si和PBZ-3Si的器件的PCE较低，分别为8.98%和9.92%。此外，PBZ-2Si:IT-M还表现出良好的厚度耐受性，其240 nm厚的活性层在储存77天后效率下降最为有限，为大规模制造提供了良好的潜力。我们的工作表明，硅氧烷封端侧链和烷基侧链的良好配对有利于优化共轭聚合物供体以用于高性能非富勒烯聚合物太阳能电池。
