The Study Of Photovoltaic Performance Based On Polycyclic D-A Conjugated Polymers

The advanced development on polymers solar cells (PSCs) was summarized in this thesis. While compared to inorganic solar cells, the PSCs show a lower power conversion efficiency(PCE). Application of conjugated polymer materias with outstanding property is one of the most important strategies to enhance the PCE of PSCs. The superiority of polycyclic D-A(donor-acceptor) polymer in PSCs comes from their extended conjugation systems facilite π-electron delocalization through the polymer backbone, reducing the bandgap and enhancing light-absorbance of the materials. In the other side, their molecular planarity favors the cofacial π-π stacking of polymer chains in the solid film, improving the charge carrier mobility. Now, the development of polycyclic conjugated D-A polymers in PSCs is rare, and high PCE hasn’t been achieved.In this work, the effects of a series of new polycyclic D-A polymers on the performance of PSCs were studied as donor materials in PSCs. The thermogravimetric anaylyses, cyclic voltammetry and UV-vis absorption spectra were used to study the effects of chemical structure of the polycyclic D-A conjugated polymers on thermostability, electrochemical properties and optical properties, respectively. In addition, the effect of carrier mobilities and active layer morphology on the photovoltaic performances were also investigated. In this work, the specific research contents and results are as follows,(1)The Poly{2,5-thiophene-alt-2,8-(4,10-bis(2-hexyldecyl))thieno[2’,3’:5,6]-pyrido-[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione} with a pentacyclic aromatic lactam acceptor unit, thieno[2’,3’:5,6]pyrido[3,4-g]thieno[3,2-c]-isoquinoline-5,11(4H,10H)-dione (TPTI) and a thiophene donor unit, was studied as donor materials in PSCs. It possesses outstanding thermostability up to434℃, and it is adequate for the application in PSCs. The film of PThTPTI got a good absorption spectra and the absorption maxima for PThTPTI in chloroform and film are583nm and623nm, respectively. The absorption onset in film locates at666nm, and thus resulted a moderate bandgap of1.86eV. On the other side, PThTPTI shows a low HOMO energy level of-5.42eV, which may lead to a high open-circle voltage(Voc). In this work, the chemical additive of DIO can effectively improve the photovoltaic performance. The optimized conventional device of PThTPTI:PC71BM bulk heterojunction PSCs afforded a PCE of7.21%, with a Voc of0.92V, a Jsc of12.47mA/cm2, and a fill factor of62.8%. The Solar cells with an inverted configuration of ITO/ZnO/PThTPTI:PC7,BM/MoO3/Ag showed a superior PCE of7.8%, with an enhanced Jsc of13.69mA/cm2and a better FF of65.6%. The inverted solar cells of PThTPTI could still have original PCE of90%after exposing in N2333hours. XRD results indicated that polymer PThTITP is partially crystalline, which accounts for its good hole mobility of1.4×10-3cm2V-1s-1.(2) The electrochemical properties, absorption and photovoltaic performance of a series of donor-acceptor (D-A) conjugated polymers (P1-P4) containing a novel pentacyclic aromatic lactam acceptor unit, thieno[2’,3’:5,6]pyrido[3,4-g]thieno[3,2-c]-isoquinoline-5,11(4H,10H)-dione (TPTI), with a donor unit, benzo-[1,2-b:4,5-b’]dithiophene (BDT) or dithieno [3,2-b:2’,3’-d]silole (DTS) were studied. The four polymers own good thermostability above300℃, which is suitable for application in PSCs. Their also possesses a deep HOMO energy level below-5.30eV, which may result a high Voc-The effects of side chains on TITP and BDT or DTS donor unit on different physical-chemical properties and photovoltaic performance were investigated. The conventional heterojunction PSCs based on Pl:PC71BM showed a highest PCE of5.30%among the four polymers.(3)The thermostability, absorption spectra, electrochemical properties and application in PSCs of new tetracyclic conjugated polymer poly{1,3-bis(4’-hexylthiophen-2-yl)-9H-indeno[1,2-b]thieno[3,4-e]pyrazin-9-one-4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b’]dithiophene}(P5) were investiaged. P5film gave a absorption range of300-1100nm and a low bandgap of1.12eV. PSCs based on P5gave a PCE of1.93%and had a broad spectral response in EQE (300-1020nm).