Advanced Ellipsometric Characterization of Conjugated Polymer Films

Abstract

Conjugated polymers are attracting worldwide attention due to their potential for use as the active layer in advanced electronic, optoelectronic, and energy harvesting applications, and their cost-effective and low thermal budget processing traits. As the technologies based on these materials develop, new and more sensitive characterization techniques are needed. Recent progress on the use of spectroscopic ellipsometry as a highly sensitive and non-invasive method to obtain fundamental information about conjugated polymer fi lms is reviewed. After a brief introduction to the practical details of the technique, the use of ellipsometry to determine optical parameters that provide insight into fi lm morphology is described, including physical phase and molecular orientation, and resulting electronic structure. The characterization of layered systems and the use of in-situ ellipsometry as a means to gain understanding of the kinetics that occur during fi lm deposition and post-deposition thermal and solvent vapor treatment is also discussed.

Sequential Processing for Organic Photovoltaics: Design Rules for Morphology Control by Tailored Semi‐Orthogonal Solvent Blends

“…[69][70][71][72][73][74] In these measurements the changes in a conjugated polymer fi lm's refractive index and thickness are monitored in a non-absorbing spectral region while the sample is exposed to controlled amounts of the co-solvent vapor (for experimental details, see the Supporting Information (SI)). Since most of the previous work on SqP is focused on P3HT, [ 20,22,37,38,48,56,57 ] we begin by examining the volume changes of swollen thin fi lms of P3HT that have varying degrees of crystallinity.…”

Plasmonic electrodes for bulk-heterojunction organic photovoltaics: a review

“…58 While most conjugated polymers tend to have optical transition dipole moments oriented along the polymer backbone chain direction [hence, transition dipoles are typically in-plane due to the edge-on and face-on orientations that most conjugated polymers take during the solution-deposition process, Figs. 9(a) and 9(b)], [100][101][102][103][104] polymers such as PVK, with the conjugation occurring on the side group rather than the polymer backbone itself, satisfy the requirement for an out-of-plane transition dipole moment. 105 Additionally, polymer chains may align in the out-of-plane direction under certain circumstances, such as during electrochemical polymerization of P3HT in the vertically oriented pores of an AAO membrane, as evidenced by photoluminescence anisotropy studies.…”

Exploring the origin of high optical absorption in conjugated polymers

“…The ability to tune the magnitude of absorption could strongly impact applications, for example, by reducing the required thickness -and thereby relaxing constraints on transport -for efficient photocurrent generation in photodetectors or solar cells, by increasing the radiative efficiency of solar cells 17 or by increasing the luminance from light emitting diodes. Figure 1 illustrates the remarkable uniformity of extinction coefficient across a wide range of conjugated polymers, as measured using spectroscopic ellipsometry 18 . Polymers of different chemical structure, self-organising tendency and optical gap lead to a maximum value of  of 0.90.1, where the complex refractive index  = nr + i.…”