Nicolas Blouin

Poly(2,7-carbazole)s: Structure−Property Relationships

Conjugated polymers combine the interesting optical and electrical properties of metals with the processing advantages and mechanical properties of traditional synthetic polymers. With clever use of a variety of synthetic tools, researchers have prepared highly pure polymers with optimized physical properties during the past 30 years. For example, the synthesis of well-defined polyacetylenes, polyphenylenes, polythiophenes, polyfluorenes, and other conjugated polymers have significantly improved the performance of these polymeric materials. However, one important class of conjugated polymers was missing from this chemical inventory: easy access to well-defined poly(2,7-carbazole)s and related polymers. This Account highlights advances in the synthesis of poly(2,7-carbazole) derivatives since they were first reported in 2001. Starting from 2-nitro-biphenyl derivatives, 2,7-functionalized carbazoles are typically obtained from Cadogan ring-closure reactions. In a second step, Yamamoto, Stille, Suzuki, or Horner-Emmons coupling polymerization leads to various poly(2,7-carbazole) derivatives. We discuss the characterization of their optical and electrical properties with a strong emphasis on the structure-property relationships. In addition, we carefully evaluate these polymers as active components in light-emitting diodes, transistors, and photovoltaic cells. In particular, several low band gap poly(2,7-carbazole) derivatives have revealed highly promising features for solar cell applications with hole mobilities of about 3 x 10(-3) cm2 V(-1) s(-1) and power conversion efficiencies up to 4.8%. Finally, we show how these new synthetic strategies have led to the preparation of novel poly(heterofluorene) derivatives and ladder-type conjugated polymers.

Highly efficient organic solar cells based on a poly(2,7-carbazole) derivative

We have studied the utilization of PCDTBT, an alternating poly(2,7-carbazole) derivative, in organic bulk heterojunction solar cells. The effect of polymer molecular weight, PCDTBT:[60]PCBM ratio, and active layer thickness on the device performance is reported. The best performance was obtained when the number-average molecular weights (Mn) are around 20 kDa with a polydispersity index around 2.2. Both PCDTBT:[60]PCBM ratio and active layer thickness affect the light absorption and the charge transport properties. By optimizing these two parameters, power conversion efficiency (PCE) up to 4.35% was reached under calibrated AM1.5G illumination of 100 mW cm−2. When blended with [70]PCBM, PCDTBT exhibited a PCE up to 4.6%.

Poly(2,7-carbazole)s and Related Polymers

This chapter reviews the recent progress made in the synthesis and characterization of carbazole-based oligomers and polymers. In fact, four classes of those p-type semiconducting materials will be presented: oligomers and polymers derived from carbazoles, indolo[3,2-b]carbazoles, diindolo[3,2-b:2′,3′-h]carbazoles, and bisindenocarbazoles. Synthetic pathways used to obtain ladder-type polymers with rod-like structure will also be reported. The characterization of the optical and electrical properties will be discussed with a strong emphasis on the structure–property relationships. Great attention will also be paid to the performances obtained with these materials used as active layers in different types of devices such as field-effect transistors, light-emitting diodes, photovoltaic cells, and thermoelectric devices.