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) × 10⁵ cm⁻¹. Bulk heterojunction OPV devices based on pairing SMBDT-S and SMBDT-SF respectively with PC₇₁BM 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.

我们已经开发了基于苯并[1,2- b：4,5- b' ]二噻吩（BDT）的新型小分子电子给体SMBDT-S和SMBDT-SF，其以噻吩侧链为核心单元并具有罗丹宁末端-封端单元以提高开路电压（V _oc），这是限制小分子有机光伏（OPV）性能的因素之一。SMBDT-S和SMBDT-SF供体分子表现出出色的热稳定性和高结晶度。发现SMBDT-S具有1.85 eV的宽带隙，具有最高的占据分子轨道（HOMO）能级为$-$5.56 eV。SMBDT-SF中的氟化导致相同的带隙为1.86 eV，甚至更低的HOMO能级为$-$5.72 eV。SMBDT-S和SMBDT-SF都具有（1.4–1.5）×10 ⁵  cm ^-1的大薄膜吸收系数。将SMBDT-S和SMBDT-SF分别与PC ₇₁ BM电子受体配对的体异质结OPV器件显示V _oc高达1.18 eV，这是报道的全小分子太阳能电池的最高V _oc之一。这些结果表明，引入氟原子和烷硫基侧链是降低HOMO能级并提高OPV中V _oc的有效策略。