Thiophene spacers impart crystallinity and enhance the efficiency of benzotrithiophene-based conjugated polymers for bulk heterojunction photovoltaics
Thiophene spacers impart crystallinity and enhance the efficiency of benzotrithiophene-based conjugated polymers for bulk heterojunction photovoltaics
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DOI：
10.1039/c2py20819a
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发表时间：
2013-01
影响因子：
4.6
通讯作者：
Shang-Che Lan;Po-An Yang;Menghua Zhu;Chia-Min Yu;Jian-Ming Jiang;K. Wei
中科院分区：
文献类型：
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作者：
Shang-Che Lan;Po-An Yang;Menghua Zhu;Chia-Min Yu;Jian-Ming Jiang;K. Wei
在这项研究中，我们合成了具有苯并三噻吩（BTT）单元作为供体和苯并噻二唑（BT）和苯并恶二唑（BO）单元分别作为受体，通过4-十二烷基噻吩间隔基连接的供体-受体共轭共聚物PBTT 4 BT和PBTT 4 BO。间隔单元的存在不仅增强了合成聚合物的溶解性，而且增强了它们在固态下的分子堆积;这两种聚合物都表现出良好的结晶度，如在它们的X射线衍射曲线中在（100）平面中的d-间距为23.8 A所证明的。当我们在本体异质结光伏器件应用中使用这些合成的聚合物时，由于PBTT 4 BO的溶解性差，结合PBTT 4 BO/PC61 BM作为活性层的最佳器件表现出3.2%的低效率，而结合更可溶的PBTT 4 BT和PC 71 BM的最佳器件表现出4.4%的效率，其比PBTTBT/PC 71 BM器件的高出1.5%，其中PBTTBT是通过在没有任何间隔基的情况下使BTT和BT单元共聚而形成的。热退火后，PBTT 4 BT/PC 71 BM器件的效率进一步提高到5.6%，VOC值为0.72 V，JSC值为11.58 mA cm-2，填充因子为67%。退火后的PBTT 4 BT/PC 71 BM活性层具有纳米级的网状形貌，棒状PBTT 4 BT结构有利于电荷的分离和传输，因此，退火后的PBTT 4 BT/PC 71 BM光伏器件的功率转换效率比铸态的PBTT 4 BT/PC 71 BM器件有很大提高.
In this study we synthesized the donor–acceptor conjugated copolymers PBTT4BT and PBTT4BO featuring benzotrithiophene (BTT) units as donors and benzothiadiazole (BT) and benzoxadiazole (BO) units, respectively, as acceptors, linked through 4-dodecylthiophene spacers. The presence of the spacer units enhanced not only the solubility of the synthesized polymers but also their molecular packing in the solid state; both of these polymers exhibited good crystallinity, as evidenced by a d-spacing of 23.8 A in the (100) plane in their X-ray diffraction curves. When we used these synthesized polymers in bulk heterojunction photovoltaic device applications, the optimal device incorporating PBTT4BO/PC61BM as the active layer exhibited a low efficiency of 3.2%, due to the poor solubility of PBTT4BO, whereas the optimal device incorporating the more-soluble PBTT4BT and PC71BM displayed an efficiency of 4.4%, which is substantially 1.5% higher than that for the PBTTBT/PC71BM device, where PBTTBT was formed by copolymerizing BTT and BT units without any spacer. After thermal annealing, the efficiency of the PBTT4BT/PC71BM device improved further to 5.6%, with a VOC value of 0.72 V, a JSC value of 11.58 mA cm−2 and a fill factor of 67%. The annealed PBTT4BT/PC71BM active layer possessed a nanoscaled network-like morphology with rod-like PBTT4BT domains that were beneficial for charge separation and transport; accordingly, the power conversion efficiency of the annealed PBTT4BT/PC71BM photovoltaic device was enhanced greatly over that of the as-cast PBTT4BT/PC71BM device.