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Controllable Growth and Charge Carrier Transport of Fibrillar Microstructure of Semiconducting Polymers in Field-Effect Transistors and Photovoltaics

Periodic Reporting for period 1 - FibrillarMICROSTRUCT (Controllable Growth and Charge Carrier Transport of Fibrillar Microstructure of Semiconducting Polymers in Field-Effect Transistors and Photovoltaics)

Reporting period: 2017-03-01 to 2019-02-28

The semiconductor technology based on inorganic semiconductors has dramatically accelerated the development of economy, health, information and energy in our modern life. In contrast, the discovery of conducting polymers in the late 1970s opened a new way for semiconductor technology (Nobel Prize in Chemistry 2000). In comparison to their inorganic counterparts, organic semiconductors exhibit obvious advantages such as low cost, light weight, mechanical flexibility, compatibility with plastic substrates, and mass production of large-area electronic devices. Due to their unique electrical properties, organic semiconductors hold a great potential in applications of organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In particular, several European multinational corporations (e.g. Philips, BASF, Siemens) and spin-off companies (e.g. CDT, Plastic Logic, Heliatek) are paving the way to a new business.
Considerable achievements have been made for conjugated polymers, but so far it is still a great challenge to tune the microstructure of semiconducting polymers in a controllable way, which allows us to further improve the device performance for both OFETs and OPVs and to deeply understand the mechanism of charge carrier transport in organic electronics.
The primary objective of this project is using solution processing to efficiently realize the controllable growth of fibrillar microstructure such as fiber size and orientation for the exactly same polymer(s), to systematically investigate the impact of their microstructure on charge carrier transport in both OFETs and OPVs (multidisciplinary), and finally to reveal the intrinsic mechanism of charge carrier transport in semiconducting polymers (interdisciplinary).
This project has resulted in seven publications in the high-impact scientific journals such as Nature Communications, Accounts of Chemical Research and Journal of the American Chemical Society.
In the field of OFETs, the Researcher reported the first polymer monolayer transistors with the record field-effect mobility over 3 cm2 V-1 s-1, which has been published in Nature Communications with the first authorship of the Researcher. Meanwhile, the Researcher summarized the recent progress and commented on the future developments of the OFET field, which was published in Accounts of Chemical Research with the first authorship of the Researcher.
In the field of OPVs, the impact of device polarity on the performance of polymer-fullerene solar cells was demonstrated (Adv. Energy. Mater.; as the first author). Further morphological optimization, with the combination of retroreflective foil, afforded a power conversion efficiency of 9.6%, among the highest for DPP-based polymer solar cells.
On the other hand, this project has supported the establishment of internal and external collaborations, and generated other four scientific research articles with the co-authorship of the Researcher. For instance, the Researcher contributed to the optical simulation for single-component solar cells (JACS 2017) and all-polymer solar cells (JACS 2018) for external collaboration. The Researcher also created close collaboration internally by measuring field-effect mobility for siloxane DPP-based polymers (RSC Advances).
These published results have also been presented as oral talks in the international and topical conferences including 14th European Conference on Molecular Electronics (2017 Dresden), International Conference on Hybrid and Organic Photovoltaics (2018 Benidorm), The International Conference on Science and Technology of Synthetic Metals (2018 Busan) and FMS annual meeting (2018 Zwolle).
In addition, the Researcher and colleagues recently has proposed a novel controllable way to modulate the polymorphism of conjugated polymers. In particular, two semi-crystalline aggregated phases were generated, which has been rarely reported. These two aggregated phases show distinctly different optical, structural and optoelectronic properties. These results go well beyond the present state of the art and a few other papers are in preparation.
As mentioned in the above section, the investigation on polymorphism is another important part of main results for this project, and a few high impact publications will be expected. More interestingly, the finding about polymorphism also initially realized the local-dependent functionalization, holding potential for developing programmable ink formulations for next-generation electronic devices.