Fine-Tuning the Energy Levels of a Nonfullerene Small-Molecule Acceptor to Achieve a High Short-Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells
Fine-Tuning the Energy Levels of a Nonfullerene Small-Molecule Acceptor to Achieve a High Short-Circuit Current and a Power Conversion Efficiency over 12% in Organic Solar Cells
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DOI：
10.1002/adma.201704904
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发表时间：
2018-01-18
影响因子：
29.4
通讯作者：
Chen, Yongsheng
中科院分区：
文献类型：
--
作者：
Kan, Bin;Zhang, Jiangbin;Chen, Yongsheng
有机太阳能电池优化需要仔细平衡材料系统的电流-电压输出。在这里，这样的优化使用超快光谱作为一种工具，以优化材料的带隙，而不改变超快电子物理的报告。通过对NFBDT的D和A单元进行修饰，设计了一种新的受体-供体-受体（A-D-A）型小分子受体NCBDT。与NFBDT相比，NCBDT的最高占据分子轨道（HOMO）能级主要由于D单元上的额外辛基而上移，最低未占据分子轨道（LUMO）能级由于A单元的取代而下移。NCBDT具有1.45 eV的低光学带隙，其将吸收范围向近红外区域扩展，向下延伸至约860 nm。然而，60 meV的降低LUMO水平的NCBDT几乎不改变V-oc水平，和海拔的NCBDT HOMO不具有实质性的影响的材料的物理性质。因此，对于NCBDT和NFBDT为基础的系统，观察到一个异常缓慢（约400 ps），但最终有效的电荷生成介导的界面电荷对状态，然后有效的电荷提取。因此，PBDB-T：NCBDT器件的功率转换效率超过12%，是溶液处理有机太阳能电池中最好的。
Organic solar cell optimization requires careful balancing of current-voltage output of the materials system. Here, such optimization using ultrafast spectroscopy as a tool to optimize the material bandgap without altering ultrafast photophysics is reported. A new acceptor-donor-acceptor (A-D-A)-type small-molecule acceptor NCBDT is designed by modification of the D and A units of NFBDT. Compared to NFBDT, NCBDT exhibits upshifted highest occupied molecular orbital (HOMO) energy level mainly due to the additional octyl on the D unit and downshifted lowest unoccupied molecular orbital (LUMO) energy level due to the fluorination of A units. NCBDT has a low optical bandgap of 1.45 eV which extends the absorption range toward nearIR region, down to approximate to 860 nm. However, the 60 meV lowered LUMO level of NCBDT hardly changes the V-oc level, and the elevation of the NCBDT HOMO does not have a substantial influence on the photophysics of the materials. Thus, for both NCBDT- and NFBDT-based systems, an unusually slow (approximate to 400 ps) but ultimately efficient charge generation mediated by interfacial charge-pair states is observed, followed by effective charge extraction. As a result, the PBDB-T: NCBDT devices demonstrate an impressive power conversion efficiency over 12%-among the best for solution-processed organic solar cells.