Charge photogeneration and transport in side-chain carbazole polymers and co-polymers

The photoconductivity, hole mobility and charge photogeneration efficiency of a series of side-chain carbazole homopolymers and copolymers (with azo side-chains) have been investigated. Cyclic voltammetry measurement of frontier orbitals energies show that the HOMO energy is determined by the nature and the position of attachment of the linker between the main chain and the carbazole, the azo-moiety being not relevant in this respect. Hole mobility is not influenced by the HOMO energy but seems to depend on the degree of conformational mobility of the side-chains, reaching values of the order of 10−3 cm2 V−1 s−1 in the best cases. The HOMO energy is instead extremely important when considering photogeneration efficiency, that can change by 10 orders of magnitude depending on the density of the carbazole side-chains in co-polymers and on the linker nature and attachment position.

Graphical abstractIn side-chain carbazole homopolymers and copolymers, the nature of the linker between the main chain and the carbazole moiety controls HOMO energy levels and charge photogeneration afficiency but not charge mobility.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► HOMO energy depends on the nature and site of attachment of chain/chromophore linker. ► HOMO energy controls charge photogeneration but not charge mobility. ► High charge mobility was measured in side-chain carbazole (co)polymers.