Benzodithiophene-based wide-bandgap small-molecule donors for organic photovoltaics with large open-circuit voltages
Benzodithiophene-based wide-bandgap small-molecule donors for organic photovoltaics with large open-circuit voltages
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DOI：
10.1016/j.orgel.2020.105996
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发表时间：
2021
影响因子：
3.2
通讯作者：
E. Lee;Duyen K. Tran;Jihun Park;Wonyoung Ko;S. Jenekhe;Y. Hwang
中科院分区：
文献类型：
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作者：
E. Lee;Duyen K. Tran;Jihun Park;Wonyoung Ko;S. Jenekhe;Y. Hwang
以苯并[1，2-B：4，5-b ']二噻吩（BDT）为原料，以噻吩侧链为核心单元，以若丹宁为封端单元，合成了新型小分子电子给体SMBDT-S和SMBDT-SF，以提高小分子有机光催化剂（OPV）的开路电压（Voc）。SMBDT-S和SMBDT-SF供体分子具有优异的热稳定性和高结晶度。发现SMBDT-S具有1.85 eV的宽带隙，最高占据分子轨道（HOMO）能级为− 5.56 eV。SMBDT-SF中的双折射导致相同的带隙为1.86 eV，甚至更低的HOMO能级为− 5.72 eV。SMBDT-S和SMBDT-SF都具有较大的薄膜吸收系数，为（1.4-1.5）× 10 5 cm− 1。基于分别将SMBDT-S和SMBDT-SF与PC 71 BM电子受体配对的本体异质结OPV器件显示出高达1.18 eV的Voc，这是所报道的全小分子太阳能电池的最高Voc之一。这些结果表明，引入氟原子和烷硫基侧链是有效的策略，以降低HOMO能级和提高OPV的V。
We have developed new small-molecule electron donors, SMBDT-S and SMBDT-SF, based on benzo [1, 2-b: 4, 5-b’] dithiophene (BDT) with thiophene side chains as a core unit and rhodanine end-capping units to enhance the open-circuit voltage (V oc), which is one of the factors limiting performance of small-molecule organic photovoltaics (OPVs). The SMBDT-S and SMBDT-SF donor molecules exhibited excellent thermal stability and high crystallinity. SMBDT-S was found to have a wide bandgap of 1.85 eV with the highest occupied molecular orbital (HOMO) energy level of− 5.56 eV. The fluorination in SMBDT-SF led to the same bandgap of 1.86 eV with an even lower-lying HOMO energy level of− 5.72 eV. Both SMBDT-S and SMBDT-SF have large thin-film absorption coefficients of (1.4–1.5)× 10 5 cm− 1. Bulk heterojunction OPV devices based on pairing SMBDT-S and SMBDT-SF respectively with PC 71 BM electron acceptor showed V oc as high as 1.18 eV, which is among the highest V oc reported for all-small-molecule solar cells. These results demonstrate that introducing fluorine atoms and alkylthio side chains are effective strategies to downshift the HOMO energy level and enhance the V oc in OPVs.