A flexible n-type organic semiconductor for optoelectronics

Abstract

n-Type organic semiconductors are important for a range of optoelectronic applications including organic photovoltaic devices, light-emitting diodes, and field effect transistors (FETs). In spite of this clear motivation there has been significantly less development of n-type compounds relative to p-type systems. We have developed a simple, small molecule n-type material, 2-[(7-{9,9-di-n-propyl-9Hfluoren-2-yl}benzo[c][1,2,5]thiadiazol-4-yl)methylene]malononitrile (K12), that can be processed either by spin-coating from solution or evaporation in vacuum. The thermal properties of K12 enable the film morphology to be controlled at easily accessible temperatures allowing the charge mobility to be tuned over two orders of magnitude. The electron mobility in the films was found to be independent of the initial processing conditions (solution or evaporation).

A Narrow Optical Gap Small Molecule Acceptor for Organic Solar Cells

“…The key to the design of YF25 is that the dicyanovinyl-benzothiadiazole unit provides the electron affi nity, [16][17][18] which coupled with the dithienosilole unit leads to the narrow optical gap (1.7 eV). The energy levels of YF25 , 60-PCBM, and P3HT estimated from cyclic voltammetry In Figure 1 c we present the thin fi lm absorption spectra of YF25 and 60-PCBM.…”

Pentacene/K12 solar cells formed by organic vapor phase deposition

“…10 K12 has been reported to have an electron mobility of 10 −3 cm 2 ∕Vs. 17 Although this mobility is lower than that of PEN (up to 40 cm 2 ∕Vs), 13 a recent article by Armin et al 20 reports that balanced carrier mobilities are not the key enabling factor for high-performance photovoltaics.…”

“…PEN was deposited with a rate of 0.2 nm∕s. K12 was synthesized as described in literature 17 and deposited at a rate of 1.1 nm∕s. The chamber pressure was set to 0.9 hPa.…”

“…17 To form homogenous thin films on large areas, organic vapor phase deposition (OVPD) technology can be used. 18 In this work, we report on the deposition of the molecule K12 in single layers as well as in bilayer devices consisting of a PEN/K12 heterojunction on indium tin oxide (ITO) by OVPD (right inset of Fig.…”

Novel materials for bulk heterojunction thin film organic photovoltaic devices - research and application

“…The effect of film morphology on the charge mobility has been investigated by two methods; first, in an organic field effect transistor configuration (undertaken by Ms Karyn Mutkins), and second, using the Photoinduced Charge Extraction in Linearly Increasing Voltage (PhotoCELIV) method (Dr Almantas Pivrikas and Mr Karsten Krueger). [130][131][132] In addition, K12 can be processed either by spin coating from solution or evaporation in vacuum and films formed by both methods were studied to determine whether the initial processing conditions (solution or evaporation) influence the electron mobility of the final film. Given the work undertaken by others, only a brief summary of the key results will be given here.…”