Synthesis and characterization of n-type organic semiconductors and their potential applications in solar cells and sensors for sport
Date of Issue2017-05-11
School of Materials Science and Engineering
During the past two decades, organic solar cells (OSCs) have attracted wide attention due to several advantages of light weight, low cost, easy processing and flexibility. Meanwhile, various usages of OSCs in wearable electronics recently imply the potential wide application of this technique in the area of sport. Growth of Power Conversion Efficiency (PCE) of OSCs has reached higher than 10% for single junction OSCs mainly through design and synthesis of novel donors (p-type semiconductors materials), optimization of film morphology and device development. However, one lagging area is the development of novel electron acceptors (n-type semiconductors materials). Nowadays, fullerene derivatives, such as PC61BM and PC71BM, are still the dominant acceptors due to their superior charge transporting properties. However, these two acceptors suffer from some intrinsic shortcomings, such as high production cost, difficult functionalization and limited absorption etc. Therefore, developing novel acceptors that can overcome the above-mentioned disadvantages is highly desirable to obtain even higher PCE. In addition to the usage of n-type semiconductors in electronic materials, their usage in sensor is also important for providing novel materials to fulfill the rapid development of wearable sensor for in situ monitor. My Ph. D research, focusing on providing novel n-type semiconductors for OSCs and sensors, can be briefly divided into the following several parts. Firstly, I focused on developing novel n-type building blocks for OSCs acceptors. By adopting the intramolecular double Friedel-Crafts-acylation (F-C acylation) method, various novel types of fused-heteroaromatic diones were obtained. Secondly, I designed and synthesized two novel fullerene-based acceptors: TQMA and TQBA considering from the idea of increasing simultaneously the absorption and LUMO energy. Occupying the matched energy level and improved film morphology, acceptor TQMA exhibited best PCE of 2.8% with donor P3HT. Thirdly, due to the toughness of functionalization for fullerene, I shifted the focus on developing other novel n-type semiconductor for non-fullerene acceptors. Considered that fullerene may have isotropic charge transport due to its 3D ball-like shape, I designed and synthesized a novel non-fullerene acceptor Me-PDI4 with tetrahedral architecture based on PDI unit. It has complementary absorption with donor materials PBDTTT-C-T, amorphous film morphology and suitable energy level and exhibited moderate PCE of 2.73%. Fourthly, I attempted to design and synthesize other novel n-type building block based on NDI. 1) I synthesized a novel NDI-core-extended building block NTI, which had single α thiophene vacant position for further transformation. Through coupling, I synthesized a series of NTI dimer and trimer, which showed not only good electron mobility, but also promising PCE about 2.5%. Further optimization elevated the value to 7%. 2) Through one-step simple thionation of NDI, I synthesized a series of S-NDI compounds with enhanced absorption and mobility as well as adjustable LUMO energy level. Although the PCE is not so promising, this method provides a useful way for further OSCs acceptor development. Finally, I designed and synthesized a K+ probe TM-1 based on n-type materials naphthalimide and 1-aza-18-crown-6 effectively within four steps. Interestingly, with different excited wavelength, it had different emission spectrum. The probing ability of TM-1 to K+ ion was studied. In conclusion, in this thesis, several n-type semiconductors for OSCs acceptors based on fullerene or non-fullerene materials have been designed and synthesized. Their photovoltaic properties were also investigated in depth. These works contributed, to some extent, to the development of the OSCs from the viewpoints of materials synthesis and methods innovations. In addition, n-type semiconductor used for sensor in this thesis also provides an alternative perspective to design novel sensor in the future.