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This journal is©The Royal Society of Chemistry 2019 Chem. Soc. Rev., 2019, 48, 1431--1433 | 1431
Cite this: Chem. Soc. Rev., 2019,
48, 1431
Materials chemistry in flexible electronics
Xiaodong Chen,a John A. Rogers,bcd Stephanie P. Lacour,e Wenping Huf andDae-Hyeong Kimgh
a Innovative Centre for Flexible Devices (iFLEX), School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore.
E-mail: [email protected] Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USAc Center for Bio-Integrated Electronics, Northwestern University, Evanston, Illinois 60208, USAd Departments of Biomedical Engineering, Neurological Surgery, Chemistry, Mechanical Engineering, Electrical Engineering, and Computer Science, Simpson Querrey
Institute for Nano/Biotechnology, Northwestern University, Evanston, Illinois 60208, USA. E-mail: [email protected] Bertarelli Foundation Chair in Neuroprosthetic Technology, Laboratory for Soft Bioelectronic Interfaces, Institute of Microengineering, Institute of Bioengineering, Centre
for Neuroprosthetics, Ecole Polytechnique Federale de Lausanne (EPFL), 1202 Geneva, Switzerland. E-mail: [email protected] Tianjin Key Laboratory of Molecular Optoelectronic Science, Department of Chemistry, School of Science, Tianjin University & Collaborative Innovation Center of Chemical
Science and Engineering (Tianjin), Tianjin 300072, China. E-mail: [email protected] Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 08826, Republic of Koreah Institute of Chemical Processing (ICP), Seoul National University, Seoul 08826, Republic of Korea. E-mail: [email protected]
Xiaodong Chen
Xiaodong Chen is a Professor ofMaterials Science and Engineeringand Professor (by courtesy) ofPhysics and Applied Physics atNanyang Technological University(NTU), Singapore. He received hisBS degree in chemistry from FuzhouUniversity (China) in 1999, MSdegree in physical chemistry fromthe Chinese Academy of Sciencesin 2002, and PhD degree inbiochemistry from the Universityof Muenster (Germany) in 2006.After working as a postdoctoral
fellow at Northwestern University (USA), he started hisindependent research career as a Singapore National ResearchFoundation (NRF) Fellow and Nanyang Assistant Professor at NTUin 2009. Since 2016, he is full professor at NTU. His researchinterests include mechano-materials and devices, integrated nano–bio interfaces, and cyber–human interfaces. He has been recognizedby several awards, including the Mitsui Chemicals-SNIC IndustryAward in Materials and Nano-chemistry (2018), Singapore NRFInvestigatorship (2016), Small Young Innovator Award (2015), andSingapore NRF Fellowship (2009).
John A. Rogers
John A. Rogers is the LouisSimpson and Kimberly QuerreyProfessor of Materials Scienceand Engineering, Biomedical Engi-neering and Medicine at North-western University, with affiliateappointments in Mechanical Engi-neering, Electrical and ComputerEngineering and Chemistry, wherehe is also Director of the newlyendowed Center for Bio-IntegratedElectronics. He has publishedmore than 650 papers, is a co-inventor on more than 100
patents and he has co-founded several successful technologycompanies. His research has been recognized by many awards,including a MacArthur Fellowship (2009), the Lemelson-MIT Prize(2011), the Smithsonian Award for American Ingenuity in thePhysical Sciences (2013), the MRS Medal (2018) – and most recentlythe Benjamin Franklin Medal from the Franklin Institute (2019). Heis a member of the National Academy of Engineering, the NationalAcademy of Sciences and the American Academy of Arts and Sciences.
DOI: 10.1039/c9cs90019e
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1432 | Chem. Soc. Rev., 2019, 48, 1431--1433 This journal is©The Royal Society of Chemistry 2019
Why this themed issue
Electronic components are going to befully portable, wearable, and even implant-able soon for the purposes of smart lifeassistance, rehabilitation, and even humanenhancement. Chemists and materialsscientists are proposing and developingnew materials and fabrication strategies toachieve the final goal of fully bio-integratedelectronics. These technological innova-tions in materials, processes, and devicedesign could give rise to a dramaticimprovement in the performance ofwearable and implantable electronics.
The combination of soft materials andactive electronic materials to achieve highflexibility and stretchability of electronicdevices has been extensively exploredin the past two decades. Materials chem-istry played key roles in this exploration,including developing new active materials,new soft elastic substrates, and new inte-gration processes of both. Traditionalactive materials, like silicon, gold, silver,carbon, and so on, have been repurposedthrough novel structural designs andintegration processes. New organic-basedelectronic components and elastic substrateshave also been developed. Although the
mobility, conductivity, and stability ofthese organic materials are waiting tobe optimized, this opens many new oppor-tunities toward the next generation ofbio-integrated electronics. Also, newsoft elastic substrates are becomingabundant and multi-functional with newsupramolecules, polymers, hydrogels, andother biomaterials based on the latestgenetic and synthetic biology technologies.These branches are growing very fast, andit is time to review and analyse all theseefforts, sum up the first stage, and drawthe next blueprint.
To showcase recent advances in thisemerging field, this themed issue wrapsup the recent efforts in the importantflexible and stretchable materials andelectronics areas and focuses on thechallenges remaining to point out futureresearch directions. The issue bringstogether contributions from leading expertsand covers the following three criticalaspects of materials chemistry in flexibleelectronics.
(1) Processing materials for highperformance flexible electronics
To achieve high-performance flexible andstretchable electronics, organic materialsand nanoscale materials are regarded asgreat candidates for such devices due to
Wenping Hu
Wenping Hu is a Professor of theSchool of Science, TianjinUniversity. He got his BS degreefrom Hunan University in 1993,MS degree from the Institute ofMetal Research, ChineseAcademy of Sciences in 1996 andPhD degree from the Institute ofChemistry, CAS (ICCAS) in 1999.Then he joined Osaka Universityand Stuttgart University as aresearch fellow of the JapanSociety for the Promotion ofSciences and Alexander von
Humboldt Fellowship, respectively. In 2003 he worked in NipponTelephone and Telegraph, and then returned to ICCAS again as afull professor. He focuses on organic optoelectronics, especiallyorganic semiconducting crystals, organic field-effect materialsand devices.
Dae-Hyeong Kim
Dae-Hyeong Kim obtained BSand MS degrees in ChemicalEngineering from Seoul NationalUniversity, Korea, in 2000 and2002, respectively. He received hisPhD degree in Materials Scienceand Engineering from theUniversity of Illinois at UrbanaChampaign in 2009. From 2009to 2011, he was a post-doctoralresearch associate at the Univer-sity of Illinois. He joined SeoulNational University in 2011 andis currently an Associate Professor
in the School of Chemical and Biological Engineering of SeoulNational University. He has published more than 100 papers and50 international and domestic patents. He has been recognized withseveral awards including the George Smith Award (2009), MRSGraduate Student Award (2009), Green Photonics Award (2011), TR35 award (2011), Hong Jin-ki Creative Award (2015), SCEJ Award(2016), and the Korea Young Scientist Award (2017).
Stephanie P. Lacour
Stephanie P. Lacour holds the Bertarelli FoundationChair in Neuroprosthetic Technology at the School ofEngineering at the Ecole Polytechnique Federale deLausanne. She received her PhD in ElectricalEngineering from INSA de Lyon, France in 2001, andcompleted postdoctoral research at Princeton University(USA) and the University of Cambridge (UK). SinceJanuary 2017, she is full professor in Microengineeringand Bioengineering at EPFL. She is a co-foundingmember and the current director of the EPFL Center forNeuroprosthetics. She is the recipient of the 2006 MITTR35, the 2011 Zonta award, the 2014 WEF YoungScientist, and she was selected as one of the 2015World Economic Forum Young Global Leaders.
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This journal is©The Royal Society of Chemistry 2019 Chem. Soc. Rev., 2019, 48, 1431--1433 | 1433
their ease of processing and excellentflexibility. Three reviews are dedicatedto elucidating how materials have beenprocessed for high performance flexibleelectronics. Significant progress in utilizingnanomaterials to achieve high-performancestretchable conductive nanocomposites forsoft electronics, optoelectronics, and energyharvesting devices is reviewed by Kimet al. (DOI: 10.1039/C8CS00706C). Howconductive nanomaterials can be inte-grated with inkjet-based manufacturingprocesses is also a key to facilitating thetranslation between research results andindustrial application of flexible electronics,which is summarized by Magdassi et al.(DOI: 10.1039/C8CS00738A). Colloidalnanocrystals of bulk group IV, III–V,II–VI, IV–VI, I–III–VI2 and metal–halide per-ovskite semiconductors are excellentfor thin film and flexible electronics. Kagan(DOI: 10.1039/C8CS00629F) summarizeshow to precisely control the synthesisand assembly of semiconducting nano-crystals for flexible electronic devices.
Three reviews are involved in elaboratingon the application of organic materials inflexible electronics. The progress andchallenges of organic crystalline materialsand their processing technologies for flex-ible transistors and resistive switchingdevice applications are summarized byHu et al. (DOI: 10.1039/C8CS00406D)and Li et al. (DOI: 10.1039/C8CS00614H).And how to design non-fullerene electronacceptors for organic solar cells isreviewed in-depth by Wadsworth et al.(DOI: 10.1039/C7CS00892A). Besides,Stadlober et al. (DOI: 10.1039/C8CS00928G)summarize the integration of ferroelectricpolymers in flexible electronics for smartsensor applications.
(2) Unusual mechanical properties ofelectronic materials and devices
In addition to the processing of activematerials, obtaining the desired mechan-ical properties of flexible devices is an
important focus for flexible deviceresearch to sustain compliance with thedynamic environments where the devicesoperate. A commonly adopted method isto integrate active materials with softmaterials such as silicone elastomersand hydrogels. A tutorial review by Skovet al. (DOI: 10.1039/C8CS00963E) con-cludes how to tailor the composition ofsilicone elastomers to achieve desiredmechanical and chemical properties insoft electronics applications. Further,Zhao et al. (DOI: 10.1039/C8CS00595H)provide a review on how to realize hydro-gel bioelectronics by discussing themechanism of tissue–electrode interac-tions and the uniqueness and rationalguidelines of hydrogels in bioelectronics.Not only soft and flexible substrates havebeen surveyed, active materials and flex-ible substrates need to be engineered andintegrated strategically. Cheng et al. (DOI:10.1039/C8CS00609A) summarize how tosoften gold through materials chemistryfor stretchable electronics. And Pei et al.(DOI: 10.1039/C8CS00834E) have surveyedmorphological/nanostructural controlsfor intrinsically stretchable organic elec-tronics to obtain both mechanical flexibil-ity and electrical properties.
From materials to devices, theassembly of multiple materials and deviceunits always requires delicate design.Both molecular design and mechanicaldesign for active materials and integrateddevices to proactively modulate mechan-ical properties of mechano-adaptabledevices are reviewed by Chen et al.(DOI: 10.1039/C8CS00801A). This greatprogress has undoubtedly promoted thefield of flexible electronics towards theapplication of wearable and implantabledevices.
(3) Wearable and implantableapplications of flexible electronics
Next-generation wearable devices shouldbe beneficial toward personalized
medicine to provide predictive analyticsand treatment. Gao et al. (DOI: 10.1039/C7CS00730B) sum up the mechanismsand recent progress in molecular analy-sis in sweat, tears, saliva, blood, etc. forwearable biosensors. Research towardssingle-platform, cost-effective, portableand fully-functional systems woulddefinitely continue progress towardsrealizing continuous personalized healthmonitoring. Furthermore, implantabledevices for neural interfaces have pro-duced further refinement in the spatio-temporal resolution, cell-type selectivity,and long-term stability of neural inter-faces. To conform with these issues,fiber-based neural probes were devel-oped and Anikeeva et al. (DOI: 10.1039/C8CS00710A) review how fiber-basedprobes work in the emerging studies ofnerve growth and repair.
Final remarks
We do hope the readers enjoy the mate-rials chemistry in flexible electronicsissue presented here, and find it inspir-ing for their future research with bloom-ing ideas and progress to further usherthe prosperity of this field. This researchis absolutely multi-disciplinary, and therelated chemical, electrical, and biome-dical investigations are closely involvedeach other. Near the end, we would liketo express our sincere appreciation toall the authors for their fabulous con-tributions to this themed issue. Withthe issue containing these excellentreview articles, we believe researchersin various fields will get a broaderand deeper understanding of flexibleelectronics. We do hope to witness moreexciting research milestones in this areain the future. Finally, we would liketo thank all the editorial staff membersof Chemical Society Reviews for theirstrong support.
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