Synthesis And Photovoltaic Properties Of Novel Low Bandgap Conjugated Copolymers Based On 2,7-Cabazole

π-conjugated polymers have attracted much attention for the pontential use as the donor materials in the polymer photovoltaic solar cells (PPVCs). Although the energy conversion efficiency of 4~7% of PPVCs have been achieved recently, it is necessary to improve the efficiency for commercial use. The optical active polymers, currently used in PPVCs devices are typically low bandgap conjugated polymer. In order to match solar terrestrial radiation, and thus improving the device efficiency, many researchers have foucsed on the synthesis of novel conjugated polymers with extending absorption.As compared with other conjugated polymer donors, poly(2,7-carbazole) derivatives (Cz) exhibit some unique merits such as excellent thermal stability duo to the rigid biphenyl structure, high hole mobility, low energy lying highest occupied molecular orbital (HOMO), and therefore can result in high air stability and high Voc. And the N-H could be modified by alkyl to give the polymer good solubility and processablity.The absorbency spectrum of poly(2,7-carbazole) derivatives could be tuned by copolymerization of 2,7-carbazole and other monomers. When copolymerized with low bandgap unit, the absorbency spectrum would red-shift because of the intramolecular charge transfer effect, thus enabling the photocurrent generation from lower energy photons.In this dissertation, the low bandgap units of 5,5-(4,7-di-2-thienyl-2,1,3-Benzoselenadia zole) (DBSe), 2,5-bis(3-octylthiophene-2-yl)-thiazole[5,4-d] thiazole (Tz), 5,7-(di-2-thienyl)- theno[3,4-b][1,4]pyrazine] (DTP), 2,3-dimethyl-5,7-(di-2-thienyl)-theno[3,4-b][1,4]pyrazine] (DMTP), 5,5-(4′,7′-di-3,4-ethylene dioxythiophene-2-yl)-2′,1′,3′-benzothiadiazole] (EBTE) were copolymerized with N-9′-heptadecanyl-2,7-carbazole by Suzuki polycondensation. And five series of low bandgap polymers were prepared to red-shift the absorbency spectrum of the copolymer.In charpter 3, alternating copolymer of Cz and DBSe (PCzDBSe) was synthesed. The spectrum response is extended to 750nm, which was 56nm red-shifted compared with its S analogue(PCDTBT). The hole mobility is estimated to be 3.9×10-4cm~2V-1s-1. Polymer solar cells (PSCs) based on the blends of PCzDBSe and [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) with a weight ratio of 1: 4 were fabricated. Under AM 1.5 (AM, air mass), 100 mW/cm~2 illumination, the devices were found to have an open-circuit (Voc) of 0.75V, a short-circuit current density (Jsc) of 7.23mA/cm~2, a fill factor (FF) of 45% and a power conversion efficiency (PCE) of 2.58%. The primary results indicate that PCzDBSe is a promising donor for polymer solar cells.In charpter 4, five copolymers based on Cz, Tz and DBT were prepared. The absorption of the polymer was red-shifted with the increasing content of DBT, and the spectrum response is extended to 696nm when the DBT content is 37.5%. Polymer solar cells were fabricated using the blend of the copolymer and PCBM as the active layer. Under AM 1.5(AM, air mass), 100 mW/cm~2 illumination, the bset device performances were recorded to be an open-circuit (Voc) of 0.85V, a short-circuit current density (Jsc) of 6.27mA/cm~2, a fill factor (FF) of 60.55% and a power conversion efficiency (PCE) of 3.45%, when the weight ratio of PCzTzDBT37:PCBM was 1:2.In charpter 5, Cz is copolymerized with DTP and DMTP The absorption response is extended to 819nm (PCzDTP) and 803nm (PCzDMTP). Polymer solar cells (PSCs) based on the blends of the two polymers and PCBM were fabricated. Under AM 1.5(AM, air mass), 100 mW/cm~2 illumination, a power conversion efficiency (PCE) of 0.41~0.99% was recorded. In charpter 6, Cz is copolymerized with EBTE. The spectrum response of PCzEBTE (726nm) is 58nm red-shift compared with its thiophene analogue PCzDBT, because the electron-donating effect of EDOT is stronger than thiophene. Polymer solar cells (PSCs) based on the blends of PCzEBTE and PCBM with a weight ratio of 1: 4 were fabricated. Under AM 1.5(AM, air mass), 100 mW/cm~2 illumination, the devices were found to have an open-circuit (Voc) of 0.8V, a short-circuit current density (Jsc) of 2.22mA/cm~2, a fill factor (FF) of 36% and a power conversion efficiency (PCE) of 0.64 %.