Imperial College London

DrKatherineStewart

Faculty of Natural SciencesDepartment of Physics

Research Associate
 
 
 
//

Contact

 

k.stewart17 Website

 
 
//

Location

 

Huxley BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

9 results found

Stewart K, Pagano K, Tan E, Daboczi M, Rimmele M, Luke J, Eslava S, Kim J-Set al., 2023, Understanding Effects of Alkyl Side-Chain Density on Polaron Formation Via Electrochemical Doping in Thiophene Polymers, ADVANCED MATERIALS, ISSN: 0935-9648

Journal article

Tan E, Kim J, Stewart K, Pitsalidis C, Kwon S, Siemons N, Kim J, Jiang Y, Frost JM, Pearce D, Tyrrell JE, Nelson J, Owens RM, Kim Y-H, Kim J-Set al., 2022, The role of long-alkyl-group spacers in glycolated copolymers for high performance organic electrochemical transistors, Advanced Materials, Vol: 34, ISSN: 0935-9648

Semiconducting polymers with oligoethylene glycol sidechains have attracted strong research interest for organic electrochemical transistor (OECT) applications. However, key molecular design rules for high-performance OECTs via efficient mixed electronic/ionic charge transport are still unclear. Herein, we synthesize and characterize new glycolated copolymers (gDPP-TTT and gDPP-TTVTT) with diketopyrrolopyrrole (DPP) acceptor and thiophene-based (TTT or TTVTT) donor units for accumulation mode OECTs, where a long-alkyl-group (C12 ) attached to DPP unit acts as a spacer distancing the oligoethylene glycol from the polymer backbone. gDPP-TTVTT shows the highest OECT transconductance (61.9 S cm-1 ) and high operational stability, compared to gDPP-TTT and their alkylated counterparts. Surprisingly, gDPP-TTVTT also shows high electronic charge mobility in field-effect transistor, suggesting efficient ion injection/diffusion without hindering its efficient electronic charge transport. The elongated donor unit (TTVTT) facilitates the hole polaron formation more localized to the donor unit, leading to faster and easier polaron formation with less impact on polymer structure during OECT operation, as opposed to the TTT unit. This is supported by molecular dynamics (MD) simulation. We conclude that these simultaneously high electronic and ionic charge transport properties are achieved due to the long-alkyl-group spacer in amphipathic sidechains, providing an important molecular design rule for glycolated copolymers. This article is protected by copyright. All rights reserved.

Journal article

Lee HKH, Stewart K, Hughes D, Barbe J, Pockett A, Kilbride RC, Heasman KC, Wei Z, Watson TM, Carnie MJ, Kim J-S, Tsoi WCet al., 2022, Proton radiation hardness of organic photovltaics: an in-depth study, Solar RRL, Vol: 6, Pages: 1-10, ISSN: 2367-198X

Recent developments of solution-processed bulk-heterojunction organic photovoltaic (OPV) cells have demonstrated power conversion efficiencies (PCEs) as high as 18% for single-junction devices. Such a high PCE in addition to its desirable lightweight property and high mechanical flexibility can realize high specific power and small stowed volume, which are key considerations when choosing PV for space missions. To take one important step forward, their resilience to ionizing radiation should be well studied. Herein, the effect of proton irradiation at various fluences on the performance of benchmark OPV cells is explored under AM0 illumination. The remaining device performance is found to decrease with increasing proton fluence, which correlates to changes in electrical and chemical properties of the active layer. By redissolving the devices, the solubility of the active layer is found to decrease with increasing proton fluence, suggesting that the active materials are likely cross-linked. Additionally, Raman studies reveal conformational changes of the polymer leading to a higher degree of energetic disorder. Despite a drop in performance, the retaining percentage of the performance is indeed higher than the current market-dominating space PV technology—III–V semiconductor-based PV, demonstrating a high potential of the OPV cell as a candidate for space applications

Journal article

Xu W, Du T, Sachs M, Macdonald TJ, Min G, Mohan L, Stewart K, Lin C-T, Wu J, Pacalaj R, Haque SA, McLachlan MA, Durrant JRet al., 2022, Asymmetric charge carrier transfer and transport in planar lead halide perovskite solar cells, Cell Reports Physical Science, Vol: 3, Pages: 1-17, ISSN: 2666-3864

Understanding charge carrier extraction from the perovskite photoactive layer is critical to optimizing the design of perovskite solar cells. Herein, we demonstrate a simple time-resolved photoluminescence method to characterize the kinetics of charge transport across the bulk perovskite and charge transfer from the perovskite layer to the interlayers, elucidating the dependence of these dynamics on film thickness, grain boundaries (GBs), and interlayers. Using asymmetric laser excitation, we selectively probe charge transport by generating charges both close to and far from the heterojunction interface and correlate these results with device performance. We observe that both film thickness and GBs affect the asymmetry between electron and hole charge transport across the bulk perovskite and charge transfer from the bulk perovskite to the respective interlayers.

Journal article

Kyeong M, Lee J, Daboczi M, Stewart K, Yao H, Cha H, Luke J, Lee K, Durrant JR, Kim J-S, Hong Set al., 2021, Organic cathode interfacial materials for non-fullerene organic solar cells, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 13506-13514, ISSN: 2050-7488

Journal article

Limbu S, Stewart K, Nightingale J, Yan H, Balamurugan C, Hong S, Kim J, Lee K, Kwon S, Kim J-Set al., 2021, Solid-State Ionic Liquid: Key to Efficient Detection and Discrimination in Organic Semiconductor Gas Sensors, ACS APPLIED ELECTRONIC MATERIALS, Vol: 3, Pages: 2152-2163

Journal article

Stewart K, Limbu S, Nightingale J, Pagano K, Park B, Hong S, Lee K, Kwon S, Kim J-Set al., 2020, Molecular understanding of a π-conjugated polymer/solid-state ionic liquid complex as a highly sensitive and selective gas sensor, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 8, Pages: 15268-15276, ISSN: 2050-7526

Journal article

Kwon S, Pak Y, Kim B, Park B, Kim J, Kim G, Jo Y-R, Limbu S, Stewart K, Kim H, Kim B-J, Jang S-Y, Kang H, Min J-W, Kim J-S, Jung GY, Lee Ket al., 2020, Molecular-level electrochemical doping for fine discrimination of volatile organic compounds in organic chemiresistors, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 16884-16891, ISSN: 2050-7488

Journal article

Nightingale J, Pitsalidis C, Pappa A-M, Tan E, Stewart K, Owens RM, Kim J-Set al., 2020, Small molecule additive for low-power accumulation mode organic electrochemical transistors, Journal of Materials Chemistry C, Vol: 8, Pages: 8846-8855, ISSN: 2050-7526

A small molecule additive, dodecylbenzenesulfonate (DBSA), is added to the electrolyte in OECTs to improve the device performance.

Journal article

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=01432899&limit=30&person=true