基于不同功能的苯并噻二唑为受体单元和低聚噻吩为给体单元的D-A-D-A-D型有机小分子光伏材料的理论计算研究

设计了四个以四联噻吩为中心给电子单元,联二噻吩为末端给电子单元,不同功能的苯并噻二唑(DOBT,BT,FBT和FFBT)为吸电子单元的有机小分子太阳能电池给体材料,分别称为DOBT-8T,BT-8T,FBT-8T和FFBT-8T.在B3LYP/6-31G(d)基组的水平上利用密度泛函和含时密度泛函理论对四个小分子进行了理论计算.详细分析了吸电子单元苯并噻二唑的结构修饰对小分子给体材料性能的影响.理论计算结果显示,不同功能的苯并噻二唑单元的引入对小分子给体材料的几何结构、禁带宽度、HOMO与LUMO能级、轨道电子密度分配、能量驱动力、开路电压和分子中的原子电荷(NPA)都有重要调节作用.相比于其它分子,以FBT为吸电子单元的FBT-8T,显示了最窄的带隙和较低的HOMO能级值.以FFBT为吸电子单元的FFBT-8T,获得了最低的HOMO能级和较为合适的禁带宽度.利用Scharber模型分别计算了基于小分子/PC61BM为活性层的光伏器件的能量转换效率(PCE),基于FBT-8T/PC61BM和FFBT-8T/PC61BM的光伏器件,将获得的PCE分别高达约4.7%和5.2%.在以上研究的基础上,推测FBT-8T和FFBT-8T是潜在的高性能的有机小分子体异质结光伏给体材料.

Effect of Structure Modification of Benzothiadiazole Acceptor Unit on the D-A-D-A-D Typed Oligothiophene Based Donor Materials for Organic Small Molecules Solar Cells:A Theoretical Study

Four D-A-D-A-D structured organic small molecules(OSMs)DOBT-8T,BT-8T,FBT-8T and FFBT-8T have been designed for organic solar cells,which contain tetrathiophene as the core donor unit,bithiophene as the termial donor unit,combining different electron-withdrawing fragments DOBT,BT,FBT and FFBT as acceptor unit,respectively.The designed four OSMs were analyzed using density functional theory(DFT)and time dependent-DFT(TDDFT)calculations at B3LYP/6-31G(d)level.The effects of structure modification of benzothiadiazole acceptor unit on modulating the electron-donating ability of OSMs were fully investigated.Results showed that the geometrical structure,the band-gap,HO-MO/LUMO energy levels,orbital spatial distribution,energetic driving force,open-circuit voltage and NPA atomic charge of these OSMs can be systematically altered by varying the electron-withdrawing properties with different benzothiadiazole acceptor units.Compared to other OSMs,FBT-8T displayed the more narrowed Eg and relatively deeper HOMO level with FBT as acceptor.FFBT-8T exhibited the most deep-lying HOMO level of the four designed OSMs and suitable Eg value by using FFBT as acceptor.The power conversion efficiencies(PCEs)of ca.4.7%and ca.5.2%were achieved by the photovoltaic devices based on FBT-8T:PC61BM and FFBT-8T:PC61BM systems,respectively,predicting with Scharber models.On the basis of these results,FBT-8T and FFBT-8T as potential OSMs donor materials for high-efficiency organic bulk hetero-junction solar cell were proposed.