不同桥联二噻吩低带隙给受体共聚物的电子结构和光物理性质的理论研究

摘要

通过计算吸收光谱性质区分用于体异质结聚合物太阳能电池的两种不同桥联低带隙给受体共聚物PCPDTBT和PSBTBT激发态特征的差异,进而通过电荷转移态(CT)特征考察二者实现电荷分离的难易程度.利用密度泛函理论的B3LYP和CAM-B3LYP方法计算PSBTBT和PCPDTBT(n=1～4)的电子结构和光谱性质.结果表明,PSBTBT与PCPDTBT的吸收光谱相似,与太阳光谱的匹配能力相当.而激子解离能表明二者的电荷转移态(CT)电荷分离的难易程度也相当.然而用Si原子取代C原子后,C-Si键长明显长于C-C键长,降低了噻吩环和烷基链间的空间位阻,从而可能有利于其结晶度的提高,更有利于载流子的传输,因此从理论上说明PSBTBT也可能具备高效太阳能电池给体材料的潜质.%The excited state characteristics of two low band gap donor-acceptor copolymers with different bridging atoms used in bulk heterojunction solar cells were analyzed through their absorption spectra. The charge transfer state features were investigated to distinguish their abilities of charge separations. The electronic structures and spectral properties of PSBTBT and PCPDTBT( n = 1-4) were investigated based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The results show that the absorption spectrum of PSBTBT is similar to that of PCPDTBT and they have similar abilities to match with the solar spectra. Meanwhile their capabilities of charge separations for the charge transfer state are simi lar to each other in terms of exciton binding energy. However when the carbon atom was replaced by the sili con atom in the main chain of the conjugated polymer the C-Si bond is significantly longer than the C—Cbond which reduces the steric hindrance between the alkyl groups and the thiophene ring. Thus this replace ment may be beneficial to the improvement of the crystallinity and increment of the carrier transport ability.These results indicate that PSBTBT may be a promising polymer material for application in polymer solar cells.