基于二噻吩并咔唑与苯并噻二唑的 D-A 型共轭聚合物的合成与表征

Because of charge transfer between donor (D) and acceptor (A) segments, D-A conjugated polymers generally have narrower band gaps, larger molecular dipole moments, and stronger intermolecular interaction, which are favorable for achieving high charge-carrier mobility. Thus, the D-A conjugated polymers is a research focus in the field of organic solar cell materials. On the other hand, fused aromatics are characterized with rigid and coplanar configurations and small reorganization energy, thereby are widely used in the design and synthesis of D-A conjugated polymers. Therefore, in this thesis, a series of D-A conjugated polymers were synthesized using dithieno[2,3-b:7,6-b]carbazole (C1) or dithieno[3,2-b:6,7-b]carbazole (C2) as donor unit and benzothiadiazole (BT) as acceptor unit, and their photophysical, electrochemical, carrier transporting and photovoltaic properties were studied in detail. The main achievements are as follows: 1. Two polymers P(BT-C1) and P(BT-C2) based on dithienocarbazole and alkoxy substituted benzothiadiazole were synthesized, and they are both amorphous. Although their molecular structures are almost the same except the positions of S atoms in dithienocarbazole units, they exhibited reverse relative absorption intensity in long and short wavelength regions. As indicated by theoretical simulation, these two polymers display distinct backbone conformation. The backbone of P(BT-C1) was curved, while that of P(BT-C2) was almost linear. Consequently, the carrier mobility of OTFT device based on P(BT-C2) was 5.4×10-3 cm2V-1s-1, higher than 1.9×10-3 cm2V-1s-1 of OTFT device based on P(BT-C1). The HOMO energy level of P(BT-C2) was 0.2 eV deeper than that of P(BT-C1), thus, the open-circuit voltage (Voc) of the OSC device based on P(BT-C2) was obviously higher. However, the short-circuit current density (Jsc) and fill factor (FF) of the OSC device based on P(BT-C1) were higher because of more obvious phase separation of its blend film with PC71BM. As a result, PCEs of the OSC devices based on two polymers were almost the same, which were both around 5%. 2. Two polymers P(C6BT-C2) and P(C6BT2F-C2) using C2 as donor and benzothiadiazole or fluoro-benzothiadiazole as acceptor were synthesized. Compared to P(BT-C2), P(C6BT-C2) exhibited higher thermal stability, deeper HOMO energy level and red-shifted absorption spectrum. After introducing F atoms into BT unit, the HOMO energy level of P(C6BT2F-C2) decreased to -5.20 eV from -5.00 eV of P(C6BT-C2). Meanwhile, the band gap was also reduced slightly. Theoretical simulation indicated that two polymers displayed more planar but more curved backbones, as compared to P(BT-C2). Upon thermal annealing at 150 oC, OTFT devices based on P(C6BT-C2) and P(C6BT2F-C2) exhibited mobilities of 4.8×10-3 and 4.9×10-3 cm2V-1s-1, respectively. Probably due to poor phase separation between polymers and PC71BM in the blend films, Jsc and FF values of the OSC devices based on P(C6BT-C2) and P(C6BT2F-C2) were relatively low and the PCEs of both polymers were below 2%