Abstract
Semiconducting polymers are composed of elongated conjugated polymer backbones and side chains with high solubility and mechanical properties. The combination of these two features results in a high processability and a potential to orient the conjugated backbones in thin films and nanofibers. The thin films and nanofibers are usually composed of highly crystalline (high charge transport) and amorphous parts. Orientation of conjugated polymer can result in enhanced charge transport or optical properties as it induces increased crystallinity or preferential orientation of the crystallites. After summarizing the potential strategies to exploit molecular order in conjugated polymer based optoelectronic devices, we will review some of the fabrication processes to induce molecular orientation. In particular, we will review the cases involving molecular and interfacial interactions, unidirectional deposition processes, electrospinning, and postdeposition mechanical treatments. The studies presented here clearly demonstrate that process-controlled molecular orientation of the conjugated polymer chains can result in high device performances (mobilities over 40 cm2·V−1·s−1 and solar cells with efficiencies over 10%). Furthermore, the peculiar interactions between molecularly oriented polymers and polarized light have the potential not only to generate low-cost and low energy consumption polarized light sources but also to fabricate innovative devices such as solar cell integrated LCDs or bipolarized LEDs.
Highlights
Conjugated polymers have been raising an increasing interest over the past two decades as they represent a low-cost alternative to silicon technology and can be considered as the most promising candidates for the generation of optoelectronic devices [1, 2]
Understanding these correlations from both theoretical and experimental points of view represents a major achievement to increase the performances of conjugated polymer devices such as polymer solar cells (PSCs), polymer light-emitting devices (PLEDs), or polymer field-effect transistors (PFETs)
As we described in the previous part of this review, addition of TCB to the active layer solution for both PFETs and PSCs can be beneficial as it induces a high degree of polymer crystallization
Summary
Conjugated polymers have been raising an increasing interest over the past two decades as they represent a low-cost alternative to silicon technology and can be considered as the most promising candidates for the generation of optoelectronic devices [1, 2]. A large number of scientific papers have been published on the effect of the process conditions over the resulting morphology, trying to understand the correlation between morphology and performances [5,6,7] Understanding these correlations from both theoretical and experimental points of view represents a major achievement to increase the performances of conjugated polymer devices such as polymer solar cells (PSCs), polymer light-emitting devices (PLEDs), or polymer field-effect transistors (PFETs). To fabricate thin films with these complimentary properties, a balance between deformability and charge transport needs to be obtained [8] Another peculiar property of conjugated polymers is that, being macromolecules, the long chains can be oriented which may lead to enhanced polymer crystallinities or enhanced directional charge mobility. After summarizing the potential strategies to improve device performances through molecular orientation, we will review some of the methods to induce molecular orientation of conjugated polymer chains at the nanoscale and correlate the resulting morphologies with the optical and electrical properties of the films and devices
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