Design, Synthesis And Properties Of Organic Photoelectronic Materials Based On Dithienocoronenediimide, Benzobisthiadiazole And Bithiazole

Organic field-effect transistors (OFETs) and organic solar cells (OSCs) have attracted great attention due to their low weight, low cost, solution-processing ability and their potential application in flexible devices. Designing and synthesizing new OFET/OSC semiconductors is one of the hottest areas in the research of organic photoelectronic materials.In this thesis, a series of polymers and small molecules were designed and synthesized and their application in OFET/OSC was studied.In Chapter 1, the basic knowledge about OFET and OSC was introduced, including the functioning principles, parameters of OFET/OSC devices and the development of OFET/OSC semiconductors. The design strategies and main content of this thesis were also outlined.In Chapter 2, dithienocoronenediimide (DTC) was coupled with several benzothiadiazole (BT)-based monomers and three polymers with deep LUMO energy levels were obtained. The OFET devices based on P(DTC-TT-BT) showed balanced charge transport mobility, with hole mobility of 0.018 cm2V-1s-1 and 0.019 cm2V-1s-1 .In Chapter 3, DTC was coupled with BDT, IDT and IDTT to gain three polymers, P(DTC-BDT), P(DTC-IDT) and P(DTC-IDTT). The OSC devices with P(DTC-IDT)/P(DTC-IDTT) as donor were fabricated and photovoltage behaviors were observed. The devices based on P(DTC-IDT) and P(DTC-IDTT) both showed high Vocs which are approximate to 1 eV.In Chapter 4, benzobisthiadiazole (BBT) was coupled with BT monomers. Different side chains, i. e.2-octyldodecyl chain and siloxane-terminated hexyl chain, were introduced to the main chain, respectively. As a result, two polymers, P(BBT-BT) and P(BBT-Si-BT) were obtained. The two polymer showed very narrow bandgap (? 1eV) and p-type OFET characteristics. For the devices of the two polymers, P(BBT-BT) showed higher mobility of 1.04 × 10-2 cm2V-1s-1 . The films of P(BBT-BT) had higher crystallinity than that of P(BBT-Si-BT), suggesting that the side chain has significant influence on the packing of polymers. A polymer with higher side chain density, namely P(BBT-BT-C), was also designed and synthesized for comparison. The photophysics and electrochemistry behavior of P(BBT-BT-C) was also researched.In Chapter 5, BBT was coupled with (E)-1,2-di(thiophen-2-yl)ethane (TVT) and 1,2-di(thiophen-2-yl)ethyne (TET), respectively. Four polymers, P(BBT-20-TVT), P(BBT-Si-TVT), P(BBT-20-TET) and P(BBT-Si-TET) were prepared and they all showed p-type OFET behaviors. Among the polymers, devices based on P(BBT-Si-TVT) showed the highest mobility of 1.17x 10'3 cm2V-1s-1 . The higher mobility of P(BBT-Si-TVT) than others could be ascribed to the enhanced planarity caused by TVT unit and the lower steric hindrance of siloxane-terminated hexyl chain.In Chapter 6, bithiazole was coupled with BBT to obtain two polymers, P(BBT-20-BTz) and P(BBT-24-BTz). Both of the polymers had quite planar configurations and deep HOMO energy levels. The OFET devices based on P(BBT-20-BTz) and P(BBT-24-BTz) exhibited air stability and high on/off ratios above 105. The high on/off ratios are the highest among the reported BBT-based polymers. P(BBT-20-BTz) displayed mobility up to 0.11 cm2V-1s-1 .In Chapter 7, bithiazole was coupled with DTC, perylene bisimide (PBI) and naphthalene diimide (NDI), respectively. As a result, four polymers, P(DTC-24-BTz), P(DTC-20-BTz), P(PBI-BTz) and P(NDI-BTz) were designed and synthesized. OSC devices were fabricated with P(DTC-20-BTz)/P(PBI-BTz) as acceptors, and the devices all showed photovoltage behaviors, illustrating that P(DTC-20-BTz) and P(PBI-BTz) have the electron-transport ability. The PCEs of devices based on P(DTC-20-BTz) and P(PBI-BTz) were 0.46%and 1.04%, respectively. The better performance of P(PBI-BTz) could be ascribed to the its non-planar configuration.In Chapter 8, we designed and synthesized four small molecule acceptors for OSC on the basis of thienobenzene-fused perylene bisimide. The four acceptors are SdiPBI-BT-20, SdiPBI-BT-11, diPBI-BT and diPBI-BT-IDT. The OSC devices based on diPBI-BT and diPBI-BT-IDT showed PCEs of 1.08%and 1.25%, respectively. SdiPBI-BT-20 exhibited better performance, with Voc of 0.95 V and a high FF of 68.7%, which are among the highest values of non-fullerene devices. SdiPBI displayed a PCE of 6.71%, which is much higher than diPBI-BT and diPBI-BT-IDT. The three molecules all showed high Vocs above 0.95 V, implying that thienobenzene-fused perylene bisimide is a potential building block to design novel non-fullerene small molecule acceptors for OSC.