The Design, Synthesis And Characterization Of 2D-Conjugated Polymer Donor Materials By Electron-Donating Side Chains Engineering For Polymer Solar Cells

With the rapid development of society, the demand of energy is increasing. However, the huge needed of traditional fossil energy, which is non-renewable, will lead to their exhaustionand enormous environmental pollution. Therefore, with its inexhaustible and clean, solar energy has attached much attention in recent years. Polymer solar cells(PSCs) have been considered to be one of the effective approach to utilize solar energy for lowcost renewable energy technology due to their unique advantages of light weight, easy fabrication and the capability to be produced on large area flexible substrates.As we known, one of the main driving force to promote the development of the polymer solar cells is the innovation of polymer donor materials. The structure of polymer donorcan be divided into two parts are conjugated backbone and side chains. It is well known that the π-conjugated backbone is the most important component in determining most of the PSC-related physicochemical properties of the conjugated polymers. Therefore, most of the research interest is placed on the polymeric backbone when designing a polymer donor. Furthermore, more and more studies have demonstrated that side chains also have considerable effect, not only in improving the solubility of polymers for solution-processed device fabrication, but also in molecular packing, electron affinity and thus the PSC device performance.. In this dissertation, we arefocusing on the design and synthesis of new conjugated polymer donors with different electron donating sidechain for broader absorption band and suitably energy levels to improve the photovoltaic properties. The main results are as follows:(1) Two electron-donating side chains(octylthio and methoxy) were strategically attached on BDTT unit to develop two new polymers(PBDTT-OS-TT-EF and PBDTTOS-TT-CF) as donor materials for polymer solar cells based on TT acceptor unit. PBDTT-OS-TT-EF and PBDTT-OS-TT-CF show broad absorption spectra and low-lying HOMO energy level of 5.34 e V and 5.46 e V, respectively. The Voc of PSC device based on PBDTT-OS-TT-CF:PC70BM(1:1.5, w/w) is as high as 1.00 V, which is the highest value for the devices based on TT-base polymers.(2) Three different electron-donating side chains(isooctyloxy, isooctylthio and isooctyl) were respectively attached on BDTT unit to develop three new polymers(PBDTT-S-DPP, PBDTT-O-DPP and PBDTT-DPP) as donor materials for polymer solar cells based on DPP acceptor unit. These three polymers show broad absorption spectra and low-lying HOMO energy level of-5.47 e V、-5.48 e V and-5.41 e V, respectively. The hole mobilities measured by SCLC of these three polymers reached 2.27×10-3 cm2 V-1 s-1, 8.56×10-3 cm2 V-1 s-1 and 1.78×10-3 cm2 V-1 s-1, respectively. The power conversion efficiency of the PSC based on PBDTT-S-DPP: PC70BM(1:2, w/w) is 4.64% with the open-voltaic circuit(Voc) of 0.80 V.(3) Isooctyloxy as electron-donating side chains was attached on thiophene π-bridge to develop three new D-A conjugated polymers(PBDTTS-OT-BT, PBDTTO-OT-BT and PBDTT-OT-BT) as donor materials for polymer solar cells based on BDTT donor unit and BT acceptor unit. These three polymers show very similar broad absorption spectra and the absorption edge of PBDTTS-OT-BT is 880 nm. Due to the high HOMO energy level,the Voc values of the PSC based on these three polymers are lower than 0.7 V. The power conversion efficiency of the PSC based on PBDTTS-OT-BT:PC70BM(1:1, w/w) is 3.15%.