Synthesis And Photovoltaic Properties Of Low Bandgap Polymers Based On Fused Ring Containing Two Thiophenes

The advances on polymers solar cells (PSCs) were summarized in this dissertation.Polymers donor materials in active layer affect power conversion efficiency (PCE) ofPSCs greatly. In order to obtain the high-efficiency polymers with low bandgaps andbroad absorption, two series of polymers containing new fused-ring electron acceptorsbenzo[1,2-b:4,5-c′]dithiophene-4,8-dione (BDTD) orcyclopenta[2,1-b:3,4-c′]dithiophene-4-one (CPDTO) were designed and synthesized.The molecular structures of these organic intermediates and polymers P1-P6werecharacterized by1H NMR and13C NMR. The thermal stability, optical properties,electrochemical properties of P1-P6were studied by thermogravimetric analyses,UV-vis absorption spectra, and cyclic voltammetry. Furthermore, the photovoltaicproperties of polymers were investigated by bulk heterojunction solar cells with P1-P6as donor materials. The main study results are listed below.1. Novel fused-ring electron acceptor unit benzo[1,2-b:4,5-c′]dithiophene-4,8-dione(BDTD) and polymers P1-P2containing BDT or DTS were synthesized. P1and P2exhibited excellent thermal stability and low bandgaps, which are1.78eV and1.63eV for P1and P2, respectively. The absorption red-shifts from solution to solid areobvious and are25nm and40nm for P1and P2, respectively. P1and P2bothpossessed low-lying HOMO energy level, which are-5.49eV and-5.33eV for P1andP2and close to ideal HOMO energy level. Low-lying HOMO leads to high Voc. PSCsbased on P1/PC61BM and P2/PC61BM achieved high PCE of2.18%and4.33%,respectively.2. Novel fused-ring electron acceptor unit cyclopenta[2,1-b:3,4-c′]dithiophene-4-one(CPDTO) and polymers P3-P6containing BDT, DTS, carbazole or fluorene weresynthesized. All polymers possess excellent solubility and low-lying HOMO energylevels, indicating that CPDTO is a good electron acceptor unit. P3and P4exhibitedlow bandgaps, broad UV-vis absorption and obvious red-shifts from solution to solid,which are46nm and19nm for P1and P2, respectively. Polymer solar cells with aconfiguration of ITO/PEDOT:PSS/P3:PC71BM/Ca/Al were fabricated and achieved aPCE of2.72%.