Imperial College London

DrHyojungCha

Faculty of Natural SciencesDepartment of Chemistry

 
 
 
//

Contact

 

h.cha

 
 
//

Location

 

G22Molecular Sciences Research HubWhite City Campus

//

Summary

 

Publications

Publication Type
Year
to

59 results found

Windle CD, Wieczorek A, Xiong L, Sachs M, Bozal-Ginesta C, Cha H, Cockcroft JK, Durrant J, Tang Jet al., 2020, Covalent grafting of molecular catalysts on C(3)N(x)H(y)as robust, efficient and well-defined photocatalysts for solar fuel synthesis, CHEMICAL SCIENCE, Vol: 11, Pages: 8425-8432, ISSN: 2041-6520

Journal article

Sachs M, Cha H, Kosco J, Aitchison CM, Francàs L, Corby S, Chiang C-L, Wilson A, Godin R, Fahey-Williams A, Cooper A, Sprick S, McCulloch I, Durrant JRet al., 2020, Tracking charge transfer to residual metal clusters in conjugated polymers for photocatalytic hydrogen evolution, Journal of the American Chemical Society, Vol: 142, Pages: 14574-14587, ISSN: 0002-7863

Semiconducting polymers are versatile materials for solar energy conversion and have gained popularity as photocatalysts for sunlight-driven hydrogen production. Organic polymers often contain residual metal impurities such as palladium (Pd) clusters that are formed during the polymerization reaction, and there is increasing evidence for a catalytic role of such metal clusters in polymer photocatalysts. Using transient and operando optical spectroscopies on nanoparticles of F8BT, P3HT, and the dibenzo[b,d]thiophene sulfone homopolymer, P10, we demonstrate how differences in the timescale of electron transfer to Pd clusters translate into hydrogen evolution activity optima at extremely different residual Pd concentrations. For F8BT nanoparticles with common Pd concentrations of >1000 ppm (>0.1 wt. %), we find that residual Pd clusters quench photogenerated excitons via energy and electron transfer on the fs – ns timescale, thus outcompeting reductive quenching. We spectroscopically identify reduced Pd clusters in our F8BT nanoparticles from the µs timescale onwards and show that the predominant location of long-lived electrons gradually shifts to the F8BT polymer when the Pd content is lowered. While a low yield of long-lived electrons limits the hydrogen evolution activity of F8BT, P10 exhibits a substantially higher hydrogen evolution activity which we demonstrate results from higher yields of long-lived electrons due to more efficient reductive quenching. Surprisingly, and despite the higher performance of P10, long-lived electrons reside on the P10 polymer rather than on the Pd clusters in P10 particles, even at very high Pd concentrations of 27,000 ppm (2.7 wt. %). In contrast, long-lived electrons in F8BT already reside on Pd clusters before the typical timescale of hydrogen evolution. This comparison shows that P10 exhibits efficient reductive quenching but slow electron transfer to residual Pd clusters whereas the opposite is the case for F8

Journal article

Lee J, Cha H, Yao H, Hou J, Suh Y-H, Jeong S, Lee K, Durrant JRet al., 2020, Toward Visibly Transparent Organic Photovoltaic Cells Based on a Near-Infrared Harvesting Bulk Heterojunction Blend, ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 32764-32770, ISSN: 1944-8244

Journal article

Cha H, Zheng Y, Dong Y, Lee HH, Wu J, Bristow H, Zhang J, Lee HKH, Tsoi WC, Bakulin AA, McCulloch I, Durrant JRet al., 2020, Exciton and Charge Carrier Dynamics in Highly Crystalline PTQ10:IDIC Organic Solar Cells, ADVANCED ENERGY MATERIALS, ISSN: 1614-6832

Journal article

Wu J, Lee J, Chin Y-C, Yao H, Cha H, Luke J, Hou J, Kim J-S, Durrant Jet al., 2020, Exceptionally low charge trapping enables highly efficient organic bulk heterojunction solar cells, Energy & Environmental Science, Vol: 13, Pages: 2422-2430, ISSN: 1754-5692

In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells. Employing transient optoelectronic and photoemission spectroscopies, we find that this blend exhibits greatly suppressed charge trapping into electronic intra-bandgap tail states compared to other polymer/non-fullerene acceptor solar cells, attributed to lower energetic disorder. The presence of tail states is a key source of energetic loss in most organic solar cells, as charge carriers relax into these states, reducing the quasi-Fermi level splitting and therefore device VOC. DFT and Raman analyses indicate this suppression of tail state energetics disorder could be associated with a higher degree of conformational rigidity and uniformity for the Y6 acceptor. We attribute the origin of such conformational rigidity and uniformity of Y6 to the presence of the two alkyl side chains on the outer core that restricts end-group rotation by acting as a conformation locker. The resultant enhanced carrier dynamics and suppressed charge carrier trapping are proposed to be a key factor behind the high performance of this blend. Low energetic disorder is suggested to be a key factor enabling reasonably efficient charge generation in this low energy offset system. In the absence of either energetic disorder or a significant electronic energy offset, it is argued that charge separation in this system is primarily entropy driven. Nevertheless, photocurrent generation is still limited by slow hole transfer from Y6 to PM6, suggesting pathways for further efficiency improvement.

Journal article

Lee J, Lee J-H, Yao H, Cha H, Hong S, Lee S, Kim J, Durrant JR, Hou J, Lee Ket al., 2020, Efficient and photostable ternary organic solar cells with a narrow band gap non-fullerene acceptor and fullerene additive, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 6682-6691, ISSN: 2050-7488

Journal article

Kosco J, Bidwell M, Cha H, Martin T, Howells CT, Sachs M, Anjum DH, Gonzalez Lopez S, Zou L, Wadsworth A, Zhang W, Zhang L, Tellam J, Sougrat R, Laquai F, DeLongchamp DM, Durrant JR, McCulloch Iet al., 2020, Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles, NATURE MATERIALS, Vol: 19, Pages: 559-+, ISSN: 1476-1122

Journal article

Cha H, Li J, Li Y, Kim SO, Kim YH, Kwon SKet al., 2020, Effects of Bulk Heterojunction Morphology Control via Thermal Annealing on the Fill Factor of Anthracene-based Polymer Solar Cells, Macromolecular Research, ISSN: 1598-5032

© 2020, The Polymer Society of Korea and Springer. Here we report a polymeric semiconductor (ODATT) comprising alkoxy anthracene (ODA) and thienothiophene (TT) polymerized by stille coupling reaction with the Pd catalyst. The optical properties of the polymer: PC71BM blend films are used by the UV-Visible absorption spectroscopy. The ODATT blends with PC71BM exhibit a maximal power conversion efficiency of 2.2% via thermal annealing treatment. Morphological analysis of the polymer: PC71BM blend films demonstrate the influence of ODATT polymer segregation on device performance by atomic force microscopy and transmission electron microscopy. We confirmed that ODATT has enhanced fill factor after thermal annealing treatment from the reduced series and shunt resistance from morphological enhancement. [Figure not available: see fulltext.].

Journal article

Wu J, Luke J, Lee HKH, Tuladhar PS, Cha H, Jang S-Y, Tsoi WC, Heeney M, Kang H, Lee K, Kirchartz T, Kim J-S, Durrant JRet al., 2019, Tail state limited photocurrent collection of thick photoactive layers in organic solar cells, Nature Communications, Vol: 10, ISSN: 2041-1723

Weanalyseorganic solar cells with four differentphotoactive blends exhibiting differing dependencies ofshort-circuit current upon photoactive layer thickness.These blends and devices are analysedbytransient optoelectronic techniques ofcarrier kinetics and densities, airphotoemission spectroscopyof material energetics, Kelvin probe measurements of work function, Mott-Schottky analyses of apparent doping density and by device modelling. We concludethat,for the device series studied, the photocurrent losswith thick active layersis primarilyassociatedwith the accumulation of photo-generated charge carriers in intra-bandgap tail states.This charge accumulation screens the device internal electricalfield, preventing efficient charge collection. Purification of one studied donor polymer is observed to reduce tail statedistribution anddensity and increase the maximal photoactive thickness forefficient operation. Ourwork suggests that selectingorganic photoactive layerswith a narrow distribution of tail states isa keyrequirement for the fabrication of efficient, high photocurrent, thick organic solar cells.

Journal article

Sung MJ, Hong J, Cha H, Jiang Y, Park CE, Durrant JR, An TK, Kwon SK, Kim YHet al., 2019, Acene-Modified Small-Molecule Donors for Organic Photovoltaics, Chemistry - A European Journal, Vol: 25, ISSN: 0947-6539

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Invited for the cover of this issue is the group of Tae Kyu An at the Korea National University of Transportation, Soon-Ki Kwon and Yun-Hi Kim at the Gyeongsang National University. The image depicts organic photovoltaics, in which fused acene cores have been used to modulate the conjugation lengths and the bulk heterojunction morphologies. Read the full text of the article at 10.1002/chem.201902177.

Journal article

Sung MJ, Hong J, Cha H, Jiang Y, Park CE, Durrant JR, An TK, Kwon S-K, Kim Y-Het al., 2019, Acene-Modified Small-Molecule Donors for Organic Photovoltaics, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 25, Pages: 12316-12324, ISSN: 0947-6539

Journal article

Cha H, Fish G, Luke J, Alraddadi A, Lee HH, Zhang W, Dong Y, Limbu S, Wadsworth A, Maria IP, Francas L, Sou HL, Du T, Kim J-S, McLachlan MA, McCulloch I, Durrant JRet al., 2019, Suppression of Recombination Losses in Polymer:Nonfullerene Acceptor Organic Solar Cells due to Aggregation Dependence of Acceptor Electron Affinity, ADVANCED ENERGY MATERIALS, Vol: 9, ISSN: 1614-6832

Journal article

Green JP, Cha H, Shahid M, Creamer A, Durrant JR, Heeney Met al., 2019, Dithieno[3,2-b:2,3-d]arsole-containing conjugated polymers in organic photovoltaic devices, Dalton Transactions, Vol: 48, Pages: 6676-6679, ISSN: 1477-9234

Arsole-derived conjugated polymers are a relatively new class of materials in the field of organic electronics. Herein, we report the synthesis of two new donor polymers containing fused dithieno[3,2-b:2′,3′-d]arsole units and report their application in bulk heterojunction solar cells for the first time. Devices based upon blends with PC71BM display high open circuit voltages around 0.9 V and demonstrate power conversion efficiencies around 4%.

Journal article

Speller EM, Clarke AJ, Aristidou N, Wyatt MF, Francàs L, Fish G, Cha H, Lee HKH, Luke J, Wadsworth A, Evans AD, McCulloch I, Kim JS, Haque SA, Durrant JR, Dimitrov SD, Tsoi WC, Li Zet al., 2019, Toward improved environmental stability of polymer:fullerene and polymer:non-fullerene organic solar cells: a common energetic origin of light and oxygen induced degradation, ACS Energy Letters, Vol: 4, Pages: 846-852, ISSN: 2380-8195

With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation.

Journal article

Seok H, Jeong S-G, Kim K-S, Junyent-Ferre AA, Cha H, Kim Met al., 2019, Instantaneous Reactive Power Reduction of Ripple-Free Resonant Buck Converter Using Bidirectional Switch, 34th Annual IEEE Applied Power Electronics Conference and Exposition (APEC), Publisher: IEEE, Pages: 3174-3179, ISSN: 1048-2334

Conference paper

Dong Y, Cha H, Zhang J, Pastor E, Tuladhar PS, McCulloch I, Durrant JR, Bakulin AAet al., 2019, The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation, Journal of Chemical Physics, Vol: 150, ISSN: 0021-9606

Recent progress in organic photovoltaics (OPVs) has been enabled by optimization of the energetic driving force for charge separation, and thus maximization of open-circuit voltage, using non-fullerene acceptor (NFA) materials. In spite of this, the carrier dynamics and relative energies of the key states controlling the photophysics of these systems are still under debate. Herein, we report an in-depth ultrafast spectroscopic study of a representative OPV system based on a polymer donor PffBT4T-2OD and a small-molecule NFA EH-IDTBR. Global analysis of the transient absorption data reveals efficient energy transfer between donor and acceptor molecules. The extracted kinetics suggest that slow (∼15 ps) generation of charge carriers is followed by significant geminate recombination. This contrasts with the "reference" PffBT4T-2OD:PC71BM system where bimolecular recombination dominates. Using temperature-dependent pump-push-photocurrent spectroscopy, we estimate the activation energy for the dissociation of bound charge-transfer states in PffBT4T-2OD:EH-IDTBR to be 100 ± 6 meV. We also observe an additional activation energy of 14 ± 7 meV, which we assign to the de-trapping of mobile carriers. This work provides a comprehensive picture of photophysics in a system representing new generation of OPV blends with a small driving force for charge separation.

Journal article

Hong J, Wang C, Cha H, Kim HN, Kim Y, Park CE, An TK, Kwon S-K, Kim Y-Het al., 2019, Morphology Driven by Molecular Structure of Thiazole-Based Polymers for Use in Field-Effect Transistors and Solar Cells., Chemistry, Vol: 25, Pages: 649-656

The effects of the molecular structure of thiazole-based polymers on the active layer morphologies and performances of electronic and photovoltaic devices were studied. Thus, thiazole-based conjugated polymers with a novel thiazole-vinylene-thiazole (TzVTz) structure were designed and synthesized. The TzVTz structure was introduced to extend the π conjugation and coplanarity of the polymer chains. By combining alkylthienyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT) or dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (DTBDT) electron-donating units and a TzVTz electron-accepting unit, enhanced intermolecular interactions and charge transport were obtained in the novel polymers BDT-TzVTz and DTBDT-TzVTz. With a view to using the polymers in transistor and photovoltaic applications, the molecular self-assembly in and their nanoscale morphologies of the active layers were controlled by thermal annealing to enhance the molecular packing and by introducing a diphenyl ether solvent additive to improve the miscibility between polymer donors and [6,6]phenyl-C71-butyric acid methyl ester (PC71 BM) acceptors, respectively. The morphological characterization of the photoactive layers showed that a higher degree of π-electron delocalization and more favorable molecular packing in DTBDT-TzVTz compared with in BDT-TzVTz leads to distinctly higher performances in transistor and photovoltaic devices. The superior performance of a photovoltaic device incorporating DTBDT-TzVTz was achieved through the superior miscibility of DTBDT-TzVTz with PC71 BM and the improved crystallinity of DTBDT-TzVTz in the nanofibrillar structure.

Journal article

Cha H, Tan C-H, Wu J, Dong Y, Zhang W, Chen H, Rajaram S, Narayan KS, McCulloch I, Durrant JRet al., 2018, An analysis of the factors determining the efficiency of photocurrent generation in polymer:nonfullerene acceptor solar cells, Advanced Energy Materials, Vol: 8, ISSN: 1614-6832

Herein, a meta‐analysis of the device performance and transient spectroscopic results are undertaken for various donor:acceptor blends, employing three different donor polymers and seven different acceptors including nonfullerene acceptors (NFAs). From this analysis, it is found that the primary determinant of device external quantum efficiency (EQE) is the energy offset driving interfacial charge separation, ΔECS. For devices employing the donor polymer PffBT4T blended with NFA and fullerene acceptors, an energy offset ΔECS = 0.30 eV is required to achieve near unity charge separation, which increases for blends with PBDTTT‐EFT and P3HT to 0.36 and ≈1.2 eV, respectively. For blends with PffBT4T and PBDTTT‐EFT, a 100 meV decrease in the LUMO of the acceptor is observed to result in an approximately twofold increase in EQE. Steady state and transient optical data determine that this energy offset requirement is not associated with the need to overcome the polymer exciton binding energy and thereby drive exciton separation, with all blends studied showing efficient exciton separation. Rather, the increase in EQE with larger energy offset is shown to result from suppression of geminate recombination losses. These results are discussed in terms of their implications for the design of donor/NFA interfaces in organic solar cells, and strategies to achieve further advances in device performance.

Journal article

Hong J, Sung MJ, Cha H, Park CE, Durrant JR, An TK, Kim Y-H, Kwon S-Ket al., 2018, Understanding Structure-Property Relationships in All-Small-Molecule Solar Cells Incorporating a Fullerene or Nonfullerene Acceptor, ACS APPLIED MATERIALS & INTERFACES, Vol: 10, Pages: 36037-36046, ISSN: 1944-8244

Journal article

Francas Forcada L, Burns E, Steier L, Cha H, Solà-Hernández L, Li X, Shakya Tuladhar P, Bofill R, García-Antón J, Sala X, Durrant Jet al., 2018, Rational design of a neutral pH functional and stable organic photocathode., Chemical Communications, Vol: 2018, ISSN: 1359-7345

In this work we lay out design guidelines for catalytically more efficient organic photocathodes achieving stable hydrogen production in neutral pH. We propose an organic photocathode architecture employing a NiO hole selective layer, a PCDTBT:PCBM bulk heterojunction, a compact TiO2 electron selective contact and a RuO2 nanoparticle catalyst. The role of each layer is discussed in terms of durability and function. With this strategically designed organic photocathode we obtain stable photocurrent densities for over 5 h and discuss routes for further performance improvement.

Journal article

Kim K, Jeon J, Ha YH, Cha H, Park CE, Kang M, Jhon H, Kwon SK, Kim YH, An TKet al., 2018, Ambipolar charge transport of diketopyrrolepyrrole-silole-based copolymers and effect of side chain engineering: Compact model parameter extraction strategy for high-voltage logic applications, Organic Electronics, Vol: 54, Pages: 1-8, ISSN: 1566-1199

© 2017 The copolymers P24DPP-silole and P29DPP-silole, each composed of diketopyrrolopyrrole (DPP) and silole derivatives, were synthesized using a Stille coupling reaction, and their electrical performances in organic field-effect transistors (OFETs) and circuits were investigated. While both the as-spun OFETs exhibited quite low field-effect hole mobility values, the OFETs subjected to thermal annealing at 150 °C exhibited typical ambipolar transport characteristics with average hole and electron mobility values of 1 × 10−1 cm2/(V s) and 2 × 10−3 cm2/(V s). Because the compact model was necessary to perform circuit design with the synthesized OFETs, a strategy for extracting compact model parameters was proposed for high-voltage logic circuit applications by using the industry standard compact Berkeley short-channel IGFET model (BSIM).

Journal article

Cha H, Wheeler S, Holliday S, Dimitrov SD, Wadsworth A, Lee HH, Baran D, McCulloch I, Durrant JRet al., 2018, Influence of blend morphology and energetics on charge separation and recombination dynamics in organic solar cells incorporating a nonfullerene acceptor, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X

Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T-2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC71BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T-2OD:FBR blends. This is assigned to the smaller LUMO-LUMO offset of the PffBT4T-2OD:FBR blends relative to PffBT4T-2OD:PC71BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T-2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells.

Journal article

Hong J, Ha YH, Cha H, Kim R, Kim YJ, Park CE, Durrant JR, Kwon S-K, An TK, Kim Y-Het al., 2017, All-Small-Molecule Solar Cells Incorporating NDI-Based Acceptors: Synthesis and Full Characterization, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 44667-44677, ISSN: 1944-8244

Journal article

Cha H, Wu J, Wadsworth A, Nagitta J, Limbu S, Pont S, Li Z, Searle J, Wyatt MF, Baran D, Kim J-S, McCulloch I, Durrant JRet al., 2017, An efficient, "burn in" free organic solar cell employing a nonfullerene electron acceptor, Advanced Materials, Vol: 29, ISSN: 0935-9648

A comparison of the efficiency, stability, and photophysics of organic solar cells employing poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3'″-di(2-octyldodecyl)-2,2';5',2″;5″,2'″-quaterthiophen-5,5'″-diyl)] (PffBT4T-2OD) as a donor polymer blended with either the nonfullerene acceptor EH-IDTBR or the fullerene derivative, [6,6]-phenyl C71 butyric acid methyl ester (PC71 BM) as electron acceptors is reported. Inverted PffBT4T-2OD:EH-IDTBR blend solar cell fabricated without any processing additive achieves power conversion efficiencies (PCEs) of 9.5 ± 0.2%. The devices exhibit a high open circuit voltage of 1.08 ± 0.01 V, attributed to the high lowest unoccupied molecular orbital (LUMO) level of EH-IDTBR. Photoluminescence quenching and transient absorption data are employed to elucidate the ultrafast kinetics and efficiencies of charge separation in both blends, with PffBT4T-2OD exciton diffusion kinetics within polymer domains, and geminate recombination losses following exciton separation being identified as key factors determining the efficiency of photocurrent generation. Remarkably, while encapsulated PffBT4T-2OD:PC71 BM solar cells show significant efficiency loss under simulated solar irradiation ("burn in" degradation) due to the trap-assisted recombination through increased photoinduced trap states, PffBT4T-2OD:EH-IDTBR solar cell shows negligible burn in efficiency loss. Furthermore, PffBT4T-2OD:EH-IDTBR solar cells are found to be substantially more stable under 85 °C thermal stress than PffBT4T-2OD:PC71 BM devices.

Journal article

Cha H, Park CE, Kwon S-K, An TKet al., 2017, Ternary blends to achieve well-developed nanoscale morphology in organic bulk heterojunction solar cells, ORGANIC ELECTRONICS, Vol: 45, Pages: 263-272, ISSN: 1566-1199

Journal article

Sung MJ, Kim Y, Lee SB, Lee GB, An TK, Cha H, Kim SH, Park CE, Kim YHet al., 2016, New dithienophosphole-based donor-acceptor alternating copolymers: Synthesis and structure property relationships in OFET, Dyes and Pigments, Vol: 125, Pages: 316-322, ISSN: 0143-7208

© 2015 Elsevier Ltd. Two donor-acceptor conjugated copolymers comprised of a novel dithienophosphole (DTP) as the acceptor unit and bithiophene (BT) or decylthiophenebenzodithiophene (DTBDT) as the donor unit were synthesized and characterized to elucidate the relationship between donor-acceptor (D-A) architecture and organic field-effect transistors (OFETs) performance. These characteristics of D-A copolymers were affected by the structural suitability of donor and acceptor units. Poly(DTP-BT) had an ordered structure that facilitated charge carrier transfer. The crystallinity of poly(DTP-BT) increased as annealing temperature (Tann) increased. In contrast, poly(DTP-DTBDT) was amorphous regardless of Tann due to the long alkyl chains of the DTBDT units. OFET devices made with poly(DTP-BT) and annealed at 200°C exhibit a highly crystalline morphology and a relatively high field-effect mobility (4.9 × 10-3 cm2/(V·s)).

Journal article

Lee J, Cha H, Kong H, Seo M, Heo J, Jung IH, Kim J, Shim HK, Park CE, Kim SYet al., 2015, Synthesis of triarylamine-based alternating copolymers for polymeric solar cell, Polymer, Vol: 55, Pages: 4837-4845, ISSN: 0032-3861

© 2014 Elsevier Ltd. Two donor-acceptor alternating copolymers based on electron-rich triarylamine, di(1-(6-(2-ethylhexyl))naphthyl)phenylamine (DNPA), and electron-deficient benzothiadiazole and benzoselenadiazole derivatives were designed and synthesized via Suzuki coupling reaction. The resulting triarylamine-based alternating copolymers PDNPADTBT and PDNPADTBS showed good solubility in common organic solvents and good thermal stability. The optical band gaps determined from the onset absorption were 1.93 and 1.81 eV, respectively. By introducing the naphthalene ring into the triarylamine, copolymers had relatively deep HOMO energy levels of -5.48 and -5.45 eV, which led to a high open circuit voltage (Voc) and good air stability for photovoltaic application. Bulk heterojunction solar cells were fabricated with a structure of ITO/PEDOT-PSS/copolymers-PC70BM/LiF/Al by blending the copolymer with PC70BM. Both blend systems showed remarkably high Voc near 0.9 V, and the highest performance of 2.2% was obtained from PDNPADTBT, with Voc = 0.88 V, Jsc = 7.4 mA/cm2, and a fill factor of 34.4% under AM 1.5 G.

Journal article

Back JY, An TK, Cheon YR, Cha H, Jang J, Kim Y, Baek Y, Chung DS, Kwon SK, Park CE, Kim YHet al., 2015, Alkyl chain length dependence of the field-effect mobility in novel anthracene derivatives, ACS Applied Materials and Interfaces, Vol: 7, Pages: 351-358, ISSN: 1944-8244

© 2014 American Chemical Society. We report six asymmetric alkylated anthracene-based molecules with different alkyl side chain lengths for use in organic field-effect transistors (OFETs). Alkyl side chains can potentially improve the solubility and processability of anthracene derivatives. The crystallinity and charge mobility of the anthracene derivatives may be improved by optimizing the side chain length. The highest field-effect mobility of the devices prepared here was 0.55 cm2/(V s), for 2-(p-pentylphenylethynyl)anthracene (PPEA). The moderate side chain length appeared to be optimal for promoting self-organization among asymmetric anthracene derivatives in OFETs, and was certainly better than the short or long alkyl side chain lengths, as confirmed by X-ray diffraction measurements.

Journal article

Kim MJ, An TK, Kim SO, Cha H, Kim HN, Xiofeng T, Park CE, Kim YHet al., 2015, Molecular design and ordering effects of alkoxy aromatic donor in a DPP copolymer on OTFTs and OPVs, Materials Chemistry and Physics, Vol: 153, Pages: 63-71, ISSN: 0254-0584

© 2014 Elsevier B.V. All rights reserved. Two p-type polymers, PONDPP and PTADPP were synthesized by Suzuki coupling reaction to investigate the effect of alkoxy aromatic donor units in diketopyrrolopyrrole (DPP)-based copolymers on OTFTs and OPVs. PONDPP containing dialkoxynaphthalene exhibits excellent field-effect performances, with a hole mobility of 0.324 cm2/V while PTADPP containing dialkoxyanthracene exhibits mobility of 4.5 × 10-3 cm2/V at 200 °C annealing. Bulk heterojunction type polymer solar cells based on these polymers as the electron donor materials, with PC71BM as the acceptor, showed maximum power conversion efficiency (PCE) of 0.9% for PONDPP and 1.1% for PTADPP under AM 1.5 illumination. From photophysical and structural studies, we found that naphthalene unit was introduced to the DPP unit to enhance more the molecular ordering compared to anthracene unit.

Journal article

An TK, Park SJ, Ahn ES, Jang SH, Kim Y, Kim K, Cha H, Kim YJ, Kim SH, Park CE, Kim YHet al., 2015, Solvent boiling point affects the crystalline properties and performances of anthradithiophene-based devices, Dyes and Pigments, Vol: 114, Pages: 60-68, ISSN: 0143-7208

© 2014 Elsevier Ltd. All rights reserved. We investigated the effects of the solvent boiling point on organic field-effect transistor (OFET) device performances in devices prepared using two newly synthesized anthradithiophene derivatives: 9,10-di(4′-pentylphenylethynyl)-anthra[2,3-b:6,7-b′]dithiophene (DPPEADT) and 9,10-bi([9′,9′-dimethyl-fluoren-2-ylethynyl])-anthra[2,3-b:6,7-b′]dithiophene (DFEADT). DPPEADT exhibited a distinct crystalline morphology whereas DFEADT was amorphous. We characterized the relationship between the molecular structures, film morphologies, and OFET device performances in devices prepared using solvents having one of three different boiling points (chlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene). 1,2,4-Trichlorobenzene, which provided the highest boiling point among the solvents tested and acted as a good solvent for DPPEADT, significantly improved the field-effect mobilities of DPPEADT devices up to 0.16 cm2/V by enhancing the crystallinity of the film. OFETs based on amorphous DFEADT films prepared using the three solvents did not provide enhanced electrical performances. The differences between the transistor performances were attributed to the degree of π-overlap, the molecular structures, and the morphological properties of the films.

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=00872014&limit=30&person=true