Integrated Calendar

In this talk, we present results for photoconductivity in substituted carbazoles. We identify the mechanism for photocarrier generation using spectral response and PL quenching in these materials. Using a simple model for transport, we estimate the mobility-lifetime product in these materials and also show that in favourable circumstances it is possible to get information about microstrucure from transport measurements. Finally we show that side groups influence the exciton binding energy in these materials.

Contacts and interfaces are key elements of, and contributors to, the performance of organic thin film devices. Due to the range of band gaps, and electron affinities and ionization energies displayed by organic molecular and polymer semiconductors, ohmic injection or extraction of charge carriers into and from organic semiconductors is always a challenge. The search for high quality, technologically viable, environmentally stable high and low work function contacts has therefore been intensive since the inception of the field. Notable efforts of the past few years have included materials like transition metal oxides for high work function contacts and a range of self-assembled monolayer schemes or surface adsorption of electron-donating molecules for low work function contacts. This talk presents two new methods to achieve good contacts, the first based on the ex-situ lamination of ultra-thin (~10 nm) doped polymer layers on organic films; the second based on the solution-deposition of a thin layer of a polymer containing aliphatic amine groups (PEIE or PIE).
The first part of the talk describes the challenge of spatially-confining chemical doping for contact purposes in a polymer film and how lamination can help circumvent the problem. We demonstrate that a properly laminated organic/organic heterojunction is transparent to charge carrier transport.[1] Finally, we show a drastic improvement in hole injection in P3HT and TFB via lamination of p-doped ultra-thin layers of the same materials.[2]
The second part of the talk addresses the “universal”, air-stable, reduction by ~ 1 eV or more of the work function of materials as different as ITO, ZnO, Au, Ag, Al, PEDOT:PSS or graphene, via solution-based application of ultra-thin films of PEIE or PIE. Application to several different organic devices is demonstrated. A preliminary explanation of the phenomenon is provided.[3]

[1]. A. Shu et al., (submitted)
[2]. A. Dai et al., (submitted)
[3]. Y. Zhou et al., Science, 336, 327 (2012)