Design, Synthesis And Properties Of Low-Band-Gap Polymers For Polymeric Solar Cells

Over the last years, there has been an increasing interest in polymeric solar cells (PSCs). Conjugated polymers are now recognized as the emerging semiconductors due to their low cost, ease of processing and flexibility. However, compared to inorganic materials, conjugated polymers have some serious limitations for photovoltaic materials because of their relatively low mobility of charge carriers and their narrow absorption bands that have poor coverage with solar spectrum. In this thesis, a series of conjugated polymers, containing of fluorene-fluorenone, bezeole- squaraines, naieran- squaraines and pyrroles-squaraines in the main chain, were synthesized and applied to the PSCs. The thermal, optical and photovoltaic properties of the polymers were studied by the numbers.Two novel low-band-gap conjugated polymers based on fluorene having fluorenone and dicyanomethylenefluorene as the electron acceptor in the main chain were synthesized. Thiophene as a electronic bridge linked the donor with the acceptor. Furthermore they possess satisfactory thermal stability and machinability. The long alkyl chain had improved the resolvable properties of resulting polymers. The UV-Vis absorption of polymers PBTOF and PBTCNF lied in the region of 300~700nm, where had a good coverage with the visible light. The polymers PBTOF and PBTCNF exhibit a correspondingly low band gap of 1.94eV and 1.86eV. For the PBTCNF/PCBM photovoltaic device, it has maximum energy conversion effciency (ECE) of 0.016%, and open-circuit voltage (Voc) of 0.75V, Isc of 0.079mA/cm2, fill factor (FF) of 0.258.Two novel low-band-gap polyfluorene maintaining the benthipzole-squaraines in the main chain were synthesized through the Suzuki coupling reaction. It was worthy to note that the deochsibenbuzole was synthesized first time by the method of microwave technique. Furthermore they possess satisfactory thermal stability. The UV-Vis absorption of polymers PFSQM and PFSQD lied in the region of 300~850nm, where had a good coverage with the visible light.A new method of polycondensation was inducted into the polymerization of the naieran and squaric acid. Two polymers PDNPS1 and PDNPS2 with the low band gap of 1.28 and 1.32eV and broad absorption of 400~900nm were obtained .There polymers with long conjugated length was synthesized through polycondensation between fluorene-ene-pyrrole derivate, benzene-ene-pyrrole derivate and squaric acid. The resulting polymers PFVPyS1, PFVPyS2 and PFVPyS3 have the broader absorptions of 400~1100nm, and exhibit extremely low band gaps of 1.194eV, 1.23eV and 1.19eV. For the PFVPyS/PCBM photovoltaic device, it has maximum energy conversion effciency (ECE) of 0.24%, and open-circuit voltage (Voc) of 0.60V, Isc of 1.06mA/cm2, fill factor (FF) of 0.38.