Synthesis And Research Of Organic/Polymeric Solar Cell Materials

Recently, bulk heterojunction polymer solar cells (PSCs), which are based on conjugated polymer donor and fullerene derivative acceptor materials, have attracted much attention in recent years, due to their advantages of easy fabrication, simple device structure, low cost, light weight, and capability to be fabricated into flexible devices. The maximum power conversion efficiency (PCE) of the PSCs has increased quickly to over8%. But the efficiency still needs to be further improved for the demand of commercialization, which at least exceed to10%. Therefore, present studies of the PSCs are mainly focused on increasing PCE of the devices, and the key point to increase the PCE is the design and synthesis of high-efficiency conjugated polymer donor and fullerene derivative acceptor photovoltaic materials.Chapter1briefly introduce the research progress, mechanism and effect factors of bulk heterojunction polymer solar cells, mainly focus on the conjugated polymer donor materials development.Chapter2synthesized and characterized a series of D-A type conjugated polymer, namely, BDT-CzBCN, BDT-CzBCHO and BDT-CzBNO2, with benzo[1,2-b:4,5-b’]dithio-phene (BDT) and carbazole donor-unit as backbone and different accept-unit, CN, CHO, NO2as side chain. Due to the different electron deficiency ability of the accept-unit, three polymers had different LUMO level with the order of BDT-CzBNO2>BDT-CzBCN> BDT-CzBCHO (absolute value) which was consistent to the Common rules that strong accepter-unit can lead to a lower LUMO. After analysis, it was found that extinction coefficient was the main factor that affects the photoelectric conversion efficiency.Chapter3synthesized and described a series of of low band gap polymers, PDTS-DTPP and PDTP-DTPP, with4,4’-Dioctyl-2,6-dibromodithieo[3,2-b:2’,3’-d]-silole (DTS) or N-(2-Ethylhexyl)dithieno[3,2-b:20,30-d]pyrrole (DTP) as donating units and diketopyrrolopyrrole (DPP) as accepting units. These polymers possessed a broader absorption extending to micrometers with the optical band gap of1.37eV and1.23eV which can well matched with the solar spectrum and enhance photocurrent. However, because of the high HOMO level of the polymers, the Voc was limited and the power conversion efficiency was low. Therefore, to find the low band-gap materials with a suitable HOMO level is the access to obtain high efficiency photovoltaic devicesIn chapter4. a p-type9-fused-ring super-molecular compound c was synthesized by3steps which can be easily formed nanoribbons by solution self-assembly. The performance of transistors with different morphology was studied and the performance of the device fabricated with nanoribbon was perfect with the mobility of0.05cm2V-1s-1which was1000times higher than the spin coating one. The advantageous carrier mobility made it may be the substitute of PCBM to be the acceptor in organic bulk heterojunction solar cells. Further optimization of these transistors and applications in OPVs is still in progress.