Thickness dependent absorption and polaron photogeneration in poly-(2-metoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene)

Abstract

A comprehensive photocurrent spectra analysis of the ITO/PEDOT:PSS/MEH-PPV/Al devices with three different poly-(2-metoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) or MEH-PPV thin-film thicknesses is used to investigate charge carrier photogeneration in this polymer. The photocurrent is calculated based on the hole polaron drift-diffusion model including Poole-Frenkel (P-F) transport. Two mechanisms (monomolecular and Langevin-type bimolecular) for hole polaron recombination are considered separately. The MEH-PPV absorption coefficient spectra dependence on the thin film thickness is experimentally determined and included in our model. By comparing the simulated photocurrent spectra to measured data in the wide range of bias voltages and for devices with different MEH-PPV film thicknesses the polaron photogeneration quantum efficiency (θp) as a function of the electric field is extracted. The θp curves obtained for different devices are perfectly fitted by the P-F expression. It is shown that polaron photogeneration process in the thin MEH-PPV films is affected by the film thickness. A unique polaron photogeneration model which accounts for the field and thickness dependences is achieved when one of the P-F parameters is left to be thickness dependent.

Complementing Graphenes: 1D Interplanar Charge Transport in Polymeric Graphitic Carbon Nitrides

“…A reasonable range for the absorption coeffi cient in typical organic crystals and (in)organic semiconductors is 10 to 10 4 5 cm −1 . [37][38][39] For both scenarios, this region is only reached in the 1D case, while especially the 3D transport calls for very low excitation densities and absorption coeffi cients. Given the proven photocatalytic activity of the samples, [ 2,18 ] we consider such low absorption values unrealistic.…”