Fabrication of low band-gap polymer solar cells using chemical vapor deposition polymerization

摘要

For the first time, insoluble poly(isothianaphthene-3,6-diyl) (PITN(3,6)) thin-film has been successfully deposited from 3,4-diethynylithiophene via chemical vapor deposition polymerization. PITN(3,6) with an optical band-gap of about 1.8 eV, is a conjugated polymer with its backbone constructed through phenyl rings. The low band-gap was expected from an idea that the quinoid state of the polymer could be stabilized by the thiophene ring fused into the phenyl ring. Electrochemical analysis further provided the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels with values of 5.0 eV and 3.2 eV respectively. PITN(3,6) was also synthesized through more conventional liquid-solution based synthesis (Bergmann cyclization). The structural analysis showed there were undesirable side reactions during the process leaving terminal alkyne groups and five membered thiophene rings within PITN(3,6) thin-film while PITN(3,6) deposited by CVDP showed very clean structure. Finally, a bi-layer heterojunction between carbonized poly(p-phenylenevinylene) and PITN(3,6) was fabricated. Without optimization, an open circuit voltage of about 300 mV was measured. Ultimately, CVDP can realize multi-layer organic optoelectronic devices on any platform because of its low substrate temperature and highly conformal coating capability.