Interface Engineering via Photopolymerization-Induced Phase

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Article

Interface Engineering via Photopolymerization Induced Phase Separation for Flexible UV-Responsive Phototransistor Haiyan Peng, Yan Yan, Yingkui Yang, Li Zhou, Wei Wu, Qi-Jun Sun, Jiaqing Zhuang, SuTing Han, Chi-Chiu Ko, ZongXiang Xu, Xiaolin Xie, Robert K. Y. Li, and Vellaisamy A. L. Roy ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b19371 • Publication Date (Web): 07 Feb 2018 Downloaded from http://pubs.acs.org on February 8, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Interface Engineering via Photopolymerization Induced Phase Separation for Flexible UV-Responsive Phototransistor Haiyan Peng,#a,b Yan Yan,#b,c Yingkui Yang,d Li Zhou,b Wei Wu,b Qijun Sun,b Jiaqing Zhuang,b Su-Ting Han,b,c Chi-Chiu Ko,e Zongxiang Xu,f Xiaolin Xie,*a Robert K. Y. Lib and Vellaisamy A. L. Roy*b a.

Key Laboratory for Material Chemistry of Energy Conversion and Storage, Ministry of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.

b.

Department of Materials Science & Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, China.

c.

College of Electronic Science and Technology, Shenzhen University, Shenzhen 518060, China.

d.

School of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074, China.

e.

Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, China.

f.

Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China.

#

These authors contribute equally to this work.

Keywords:

UV

sensor,

photodetector,

phototransistor,

photopolymerization, click chemistry, semiconductor, thiol-ene

ACS Paragon Plus Environment

interface

engineering,

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Interface engineering has been recognized to be substantially critical for achieving efficient charge separation, charge carrier transport and enhanced device performance in emerging optoelectronics. Nevertheless, precise control of interface structure using current techniques remains a formidable challenge. Herein, we demonstrate a facile and versatile protocol wherein in-situ thiol-ene click photopolymerization-induced phase separation is implemented for constructing heterojunction semiconductor interfaces. This approach generates continuous mountain-like heterojunction interfaces that favor efficient exciton dissociation at the interface, while providing a continuous conductive area for hole transport above the interface. This facile, low-temperature paradigm presents good adaptability to both rigid and flexible substrates, offering high performance UV-responsive phototransistors with normalized detectivity up to 6.3 × 1014 cm Hz1/2 W-1 (also called Jones). Control experiments based on ex-situ photopolymerization and in-situ thermal polymerization are also implemented to demonstrate the superiority of this novel paradigm.


Page 2 of 33

Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION The precise construction of predesigned interface between layers has been widely recognized to be critical in emerging optoelectronics, such as photodetectors, sensors, solar cells and optical memories, for achieving precise and efficient control of charge separation, charge carrier transport and enhancement of device performance.1-6 Even though a variety of interfaces such as bulk heterojunction and small molecule/polymer blends have been demonstrated to offer improved optoelectronic performance,5-8 the precise control of interface structures to form predesigned junctions, remains a formidable challenge albeit necessary pursuit. As such, novel paradigms are highly awaited. Since the seminal work of Kolb, Finn and Sharpless,9 click chemistry has been one center of modern chemical science,10-23 due to its unique features including but not limited to atomic economy, reliability, specificity, mild reaction condition, tolerance to solvent, functional orthogonality, and amenability to commercially available starting materials. The marriage of photochemistry and click chemistry endows click reactions the added spatiotemporal control capability.17-23 Nevertheless, despite of the successful deployment of click chemistry on the chemical synthesis,10,17 patterning,22-25 surface functionalization,26,27 materials formation,28 and bio-scaffolds construction,29,30 the advantages of click chemistry is barely explored for precise interface engineering in emerging organic optoelectronics. UV-responsive visible-blind optoelectronic devices have garnered considerable attention for decades because of their immense utility in environmental monitoring, space communication, flame alarming, chemical sensing, biological analysis, and military defense.31,32 To exert a better control of the light detection, field-effect transistor-based33,34 light detectors, namely, phototransistors, have been employed.



Page 4 of 33

These devices typically comprise three-terminals, i.e., source, drain and gate, with light as the “fourth” terminal to generate and/or control the photon induced free charge carriers. These devices have the unique capabilities of realizing light detection, photon modulation, electric field controlled switching and signal magnification in a single device.2,8,35,36 In addition, the field-effect transistor architectures can enable phototransistors, as critical elements, to be merged into modern advanced integrated devices. More importantly, the gate terminal allows for application of an electric bias, which affords an added efficient route to facilitate photoinduced exciton dissociation and subsequent free charge carrier generation, resulting in highly photosensitive and responsive devices with decreased noise.2,8,37 Despite that numerous UV-responsive phototransistors have been reported, the fundamental relationship between interface structure and device performance is not fully disclosed. Herein, we present a novel protocol in which the heterojunction semiconductor interfaces are generated in-situ via a photo-mediated thiol-ene click reaction and subsequent phase separation of homogeneous semiconductor/monomer mixtures. Insitu photopolymerization induced phase separation has been extensively employed to form electro-optical devices such as holographic polymer dispersed liquid crystals with in plane phase separated structures.38-41 Nevertheless, photopolymerization induced phase separation in vertical direction is rare. One smart example has been demonstrated by Broer and co-workers that is known as photo-enforced stratification for single-substrate liquid crystal display, where the liquid crystalline small molecules are controlled underneath the growing polymer.42 In the present situation, the semiconductor

is

pushed

up

to

the

top

of

growing

polymer

during

photopolymerization. This novel approach generates continuous mountain-like heterojunction interfaces that favor efficient exciton dissociation at the interface, while


Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


providing a continuous conductive area for hole transport above the interface, thus offering high performance UV-responsive phototransistors with a normalized detectivity of 6.3 × 1014 Jones. Furthermore, this versatile protocol discards complicated polymer synthesis, and allows for easy design, manufacturing, and functionalization of devices by employing the vast commercially available monomers and semiconductors. The good adaptability to various substrates including rigid silicon wafer and flexible polymer sheets at low temperature promises this in-situ single-step protocol to be employed in numerous practical applications.

RESULTS AND DISCUSSION Photo-mediated thiol-ene click reaction allows for forming ideal, uniform, and homogeneous cross-linked polymer networks in a step-growth polymerization manner (Scheme 1a),14,21 and the broad availability of sulfur as a major by-product in oil industry makes the thiol-ene reaction very easy to access and implement.13 When a trithiol reacts with a triene, a cross-linked network can be formed once the functional group conversion exceeds the gel point conversion of 50% on the basis of FloryStockmayer

criteria.39

mercaptopropionate)

As (i.e.,

a

proof

of

TMPTMP)

concept, and

trimethylolpropane

tris(3-

1,3,5-triallyl-1,3,5-triazine-

2,4,6(1H,3H,5H)-trione (i.e., TATATO) were utilized as the trithiol and triene monomers, respectively, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (i.e., C8-BTBT) was employed as the semiconductor (Scheme 1b). BTBT semiconductors exhibit good UV responsive characteristics,8 and also have good solubility, which allows for low-temperature spin-coating and inkjet printing,43,44 and high carrier mobility (calculated to be up to 40 cm2 V-1 s-1).6,43 When the homogeneous mixture of C8-BTBT, TMPTMP and TATATO is exposed to light in the presence of



photoinitiator, a photopolymerized semiconductor blend is expected via photoclick reaction induced phase separation, as illustrated in Scheme 1c.

Scheme 1. Photopolymerized Semiconductor Blend Formed via Thiol-Ene Photoclick Reaction Induced Phase Separation. (a) Reaction Mechanism of the Photo-Mediated Thiol-Ene Click Reaction. (b) Chemical Structures of C8-BTBT, TMPTMP and TATATO. (c) Photopolymerized Semiconductor Blend Formed via Thiol-Ene Photoclick Reaction Induced Phase Separation Using the Homogeneous Mixture of C8-BTBT, TMPTMP and TATATO.

For precise characterization of the correlation between interface structure and device performance, phototransistors with bottom-gate top-contact architecture were first fabricated on a heavily n-doped silicon wafer (Fig. 1a). The photopolymerized semiconductor blend is formed by in-situ photopolymerization of a homogeneous solution in chloroform comprising stoichiometrically equivalent TMPTMP and TATATO as monomers, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as the photoinitiator, and the p-type semiconductor C8-BTBT. The concentration of C8BTBT in the semiconductor layer is optimized to be 60 wt%. Fourier transform


Page 6 of 33

Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


infrared (FT-IR) spectra confirmed the quantitative reaction between TMPTMP and TATATO which offered a uniform network upon exposure to 20 mW cm-2 of 365 nm light for 30 min (Fig. 1b and Fig. S1).20 Photopolymerization of homogeneous mixture comprising thiol-ene monomers and C8-BTBT led to the formation of a photopolymerized semiconductor blend with a thickness of around 35 nm, in which 12 nm for the bottom polythioether and 23 nm for the top C8-BTBT. The thickness was measured using ellipsometry as detailed in the experimental section.

Figure 1. Photopolymerized phototransistor. (a) Schematic representation of the formed phototransistor with bottom-gate top-contact architecture. (b) FT-IR spectra of the photopolymerized thiol-ene system upon exposure to 20 mW cm-2 of 365 nm light. Both the thiol and ene functional group conversions were calculated to be ~100%, indicating the formation of an ideal cross-linked polythioether network.

The photopolymerized semiconductor blend shows two strong UV-vis absorption peaks centered at 250 and 358 nm, respectively (Fig. 2a), which are primarily dominated by that of C8-BTBT. In addition, it exhibits p-type semiconductor features according to the transfer characteristics and output curves in the formed phototransistor (Fig. 2b and S2). Increasing the negative gate bias (VGS) gives rise to a higher drain-source current (IDS) that eventually reaches saturation. Before 350 nm light exposure, the turn-on gate bias is around -8 V, and the on/off ratio of IDS could reach 1.8 × 104 upon application of a VGS of -30 V. Upon exposure to 4 mW cm-2 of



350 nm UV light, the turn-on gate bias shifts positively to 7 V and the on/off ratio of the IDS decreases to 1.5 × 103 due to the generation of a photocurrent, which is verified by the dramatic increase in the calculated charge carrier mobility from 7.5 × 10-3 to 1.3 × 10-2 cm2 V-1 s-1. Deep electron trapping is expected to result in low mobility, but is profitable for a light detector by increasing the photocurrent/dark ratio.45 The positive shift of turn-on gate bias is assumed to be caused by the increased hole density derived from electron-hole pair formation under UV irradiation.8 The charge carrier density (∆N*) is estimated to be 3.6 × 1012 cm-2 from the shift of the threshold voltage (∆Vth) (i.e., from -11.5 to 1.9 V) based on the equation: ∆N* = Ci∆Vth/e, where Ci is the specific capacitance that is measured to be 28 nF cm-2 (the total capacitance with cross-linked polythioether and 100 nm SiO2 as the insulating layers which were connected in series), and e is the elementary charge (1.6 × 10-19 Coulombs).8 Nevertheless, the higher charge carrier density is not sufficient to offer a higher photocurrent and on/off ratio. To test the hypothesis, another type of phototransistor was also prepared by utilizing thermal polymerization, on the basis of the fact that thiol-ene click reactions can be triggered by heating. Systematic experiments demonstrated that acceptable phototransistors could be formed by treatment at the optimized temperature of 70 oC for 60 min (Fig. S3). Upon exposure to 4 mW cm-2 of 350 nm UV light, the threshold voltage of the thermally cured phototransistor shifts from -6.6 to 5.8 V, giving rise to a charge density of 3.4 × 1012 cm-2, but the mobility of the device is only 6% of that for the photopolymerized phototransistor (7.5 × 10-4 cm2 V-1 s-1), and the on/off ratio decreases sharply from 2.6 × 103 to 73 (Fig. S4). The unsatisfactory performance of the thermally cured phototransistor is suspected to be associated with the non-uniform and disconnected morphology.


Page 8 of 33

Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. UV light response of the photopolymerized phototransistor. (a) UV-vis absorption spectra of C8-BTBT, cross-linked polythioether and photopolymerized semiconductor blend which were spin-cast on UV transparent square quartz slides. (b) Transfer characteristics of the photopolymerized phototransistor in dark and upon exposure to 4 mW cm-2 of 350 nm light. The transfer characteristics were scanned from 10 to -30 V at a step of -0.5 V, and the applied VDS = -30 V. (c) Light response of the photopolymerized phototransistor upon exposure to 4 mW cm-2 of 350 nm light at a VGS = 0 V and VDS = -30 V. A pulse of gate bias (VGS = -30 V and VDS = 0 V) was used to reset the device to the low conductivity state in dark.

Atomic-force microscopy (AFM) images confirm that randomly distributed seaisland crystalline grains are formed by thermal polymerization, which is expected to hinder the charge transport and collection, while a continuous surface with a good uniformity (RMS = 3 nm) is afforded by photopolymerization (Fig. S5). Curing temperature-dependent surface morphology demonstrates that it is hard to achieve comparable device performance via in-situ thermal polymerization owning to the nonuniform feature even at low temperature (Fig. S6). Actually, thermally cured phototransistors are far beyond satisfying not only because of their energy consuming nature, even worse, their bad reliability with remarkable batch-to-batch variations. These results indicate that photopolymerization is superior to thermal polymerization



for constructing a phototransistor, although the crystal structure is identical in all samples, as verified by the out-of-plane X-ray diffraction (XRD) patterns (Fig. S7).44,46 As well-recognized, the photopolymerization kinetics and gelation plays a critical role on the materials properties and devices performance,19,20,38 better device performance is able to be offered with an increase of curing time up to 30 min (Fig. S8 and S9). We characterized the substrate temperature during UV irradiation, and found out that the temperature increased to 40, 65 and 68 ºC after being irradiated for 10, 20 and 30 min. The increased substrate temperature is expected to be helpful for the removal of residual chloroform and increasing the monomer reactivity during photopolymerization, and thus to facilitate the formation of condensed semiconductor. To be noted that, the low temperature in the first 10 min is important for the formation of continuous rather than isolated semiconductor region. The semiconductor C8-BTBT exhibits good light response capability, even without application of a gate bias.8 As displayed in Fig. 2c, the dark current is around 5 × 10-11 A for the phototransistor at VDS of -30 V and VGS of 0 V. Upon exposure to 4 mW cm-2 of 350 nm UV light (VGS = 0 V and VDS = -30 V), the IDS value increases sharply and then reaches a plateau in the order of 10-6 A. When the light is switched off, the maximum IDS declines quickly. The rise time and decay time are measured to be around 21 and 16 s, which are the durations taken to reach 90% and 10% of the maximum of IDS when rising and decaying, respectively. Nevertheless, it would take an extremely long time for the device to return to the low conductivity state because of the optical memory effect (Fig. S10). The phototransistor can be reset by applying a negative gate bias. When a gate voltage pulse (VGS = -30 V and VDS = 0 V) is applied, and the bias removed, the phototransistor is able to return to its low conductivity state. It is interesting that the photocurrent increases after applying the writing-reset


Page 10 of 33

Page 11 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


program, giving rise to a photocurrent/dark ratio of 1.0 × 105, upon exposure to 4 mW cm-2 of 350 nm UV light (VGS = 0 V and VDS = -30 V). The large photocurrent and photocurrent/dark ratio can enable these devices for driving and switching displays.35 In the fourth light response cycle, the rise time is 26 s upon exposure to 4 mW cm-2 of 350 nm UV light (VGS = 0 V and VDS = -30 V), and the decay time is 1 s when switching off the UV light. The photopolymerized phototransistors show no deterioration even after 50 on/off cycles, and they are stable under inert atmosphere for at least 3 months. To be noted, the IDS value is different in Fig. 2b and 2c at the point of VGS = 0 V and VDS = -30 V upon exposure to 350 nm UV light. This difference is supposed to be caused by the rapid scan and slow accumulation of charge carriers during the scan of transfer characteristics. In addition, the difference is expected to be enlarged by rougher interface. The phototransistor responsivity, which directly reflects the sensitivity upon photo-irradiation, is calculated to be 2.5 A W-1, as the product of the generated photocurrent (Jph) divided by the incident optical power (Llight).2 To normalize for variations in the device area and response speed and thus enable comparison

among

different

devices,47 the

normalized

detectivity,

D*

=

(Jph/Llight)/(2eJd)1/2, is usually employed as the figure of merit for light detectors, where Jd is the dark current.2,47 The normalized detectivity is calculated to be 6.3 × 1014 Jones, which is a significant value for a light detector.48 The light response of the phototransistor fabricated via thermal polymerization was measured. Upon exposure to 4 mW cm-2 of 350 nm UV light (VGS = 0 V and VDS = -30 V), the largest photocurrent is 20 times smaller than that for the photopolymerized phototransistor, and the responsivity, photocurrent/dark ratio and normalized detectivity are only 0.1 A W-1, 4.0 × 103, and 2.7 × 1013 Jones, respectively (Fig. S11), confirming that



photopolymerization is a judicious choice for fabricating high performance UV responsive phototransistor.

Figure 3. Emission spectra for (a) the pure C8-BTBT, and (b) photopolymerized semiconductor blend. The significant change in the emission spectra indicates strong electron-trapping at the interface between C8-BTBT and cross-linked polythioether.

To gain deeper insight into the photoresponse of the phototransistor based on photopolymerization, emission spectra are recorded for these semiconductor layers on square quartz slides (Fig. 3). Upon excitation at 350 nm, the emission spectrum of pure C8-BTBT is characterized by three peaks centered at ~370, ~430, and ~740 nm, respectively, and the intensity of the first peak is 3 times larger than that of the second peak. However, the second emission peak of photopolymerized blend is red shifted by around 10 nm, and the emission intensity of the first peak is only 0.8 times of that of the second peak, which implies strong electron trapping at the interface between the semiconductor C8-BTBT and cross-linked polythioether, accompanied by short-range charge-transfer.4,49 Apart from the strong interaction and charge-transfer between the semiconductor C8-BTBT and cross-linked polythioether, the unique interface is expected to be the primary reason for the high light responsivity and fast response speed.


Page 12 of 33

Page 13 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To understand the in-situ photopolymerization-induced phase separation structure of the semiconductor layer, we firstly examine the surface energy of the semiconductor layer via water contact angle experiments. As shown in Fig. 4a-c, the contact angle of photopolymerized polythioether is 66o, indicating its hydrophilic nature. In contrast, both the pristine semiconductor C8-BTBT and in-situ photopolymerized blend exhibit hydrophobicity with a contact angle of 100o, unambiguously demonstrating the phase separation with the small molecule semiconductor layered on the top, distinct from the thermally-cured semiconductor blend (Fig. S12).

Figure 4. Phase separated structure investigation. Contact angle results on the surface of (a) photopolymerized polythioether, (b) C8-BTBT, and (c) in-situ photopolymerized blend of polythioether and C8-BTBT, separately. (d) C1s, (e) N1s, and (f) O1s XPS spectra for the polythioether, C8-BTBT and in-situ photopolymerized blend, respectively.



Since the small molecular C8-BTBT has no oxygen and nitrogen elements and ester groups but the polythioether has, it is easy to identify the vertical structure with C8-BTBT layered on the top surface of polythioether using X-ray photoelectron spectroscopy (XPS) analysis. As illustrated in Fig. 4d, two C1s peaks corresponding to the C-C bond and O-C=O bond, centered at 284.3 and 288.3 eV, respectively, are evident in the XPS profile of the photopolymerized polythioether. Nevertheless, the C1s peak corresponding to the C-C bond is shifted to 283.8 eV for the C8-BTBT film, and no C1s peak related to the O-C=O bond is observed. In addition, the N1s and O1s peaks of the polythioether, respectively centered at 399.9 and 531.5 eV, are not observed for the semiconductor C8-BTBT (Fig. 4e and 4f), in good accordance with the chemical structures of TMPTMP, TATATO and C8-BTBT shown in Scheme 1b. The XPS spectrum of the photopolymerized semiconductor blend is almost identical to that of C8-BTBT, verifying the vertical phase-separated structure with C8-BTBT layered on the top. By contrast, for the thermally cured semiconductor blend, the C1s, N1s, and O1s peaks in the XPS profile are clear and similar to those of polythioether, albeit with different intensities, implying incomplete coverage of polythioether by C8BTBT (Fig. S13 and S14). To be noted, since both polythioether and C8-BTBT hold the Sulphur (S) element, XPS data considering S cannot identify the phase separated structure. After boiling the photopolymerized semiconductor blend in chloroform at 70 oC for 12 h, all small molecules of C8-BTBT are expected to be removed, while leaving the pure cross-linked polythioether on the silicon wafer. The tilted-view scanning electron microscopy (SEM) image confirmed the formation of a tightly cross-linked polymer network with a rough surface (Fig. 5a), completely distinct from the smooth silicon surface (Fig. S15). The atomic-force microscopy (AFM) image demonstrates


Page 14 of 33

Page 15 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the continuous mountain-like rough surface with a RMS of 2.3 nm (Fig. 5b). It should be pointed out that the mountain-like surface is only formed during in-situ photopolymerization of homogeneous mixtures comprising monomers and the small molecule semiconductor. The photopolymerization of pure monomers generated a quite smooth polythioether film only, with a RMS of 0.6 nm (Fig. 5c). Furthermore, the mountain-like interface could be easily tuned by changing the semiconductor content (Fig. S16), leading to dramatically different transfer characteristics and light responses (Fig. S17 and S18). No transistor characteristics are detected for the device with less than 30% C8-BTBT, primarily due to the strong barrier for hole transport that is supposed to occur in the several molecular layers above the interface in fieldeffect transistor devices.50 The high dependence of the structure and performance on the semiconductor concentration makes this approach versatile for tuning the interface of other various optoelectronic devices.

Figure 5. Interface of the semiconductor layer. (a) 25o tilted-view SEM image for the in-situ photopolymerized blend after removal of C8-BTBT by chloroform at 70 oC. (b) AFM image for the in-situ photopolymerized blend after removal of C8-BTBT by chloroform at 70 oC. (c) AFM image for the neat photopolymerized polythioether after treatment by chloroform at 70 oC.

We hypothesize that the in-situ photopolymerization-induced phase separation, which not only affords a certain amount of continuous mountain-like heterojunction



interfaces between the cross-linked polythioether and C8-BTBT for efficient exciton dissociation at the interface, but also provides a continuous conductive area for hole transport and collection on the top of the interface (Fig. 6a). This leads to a high photocurrent, responsivity and fast light response. Though rich mountain-like heterojunction interfaces can also be achieved via thermal polymerization-induced phase separation, the disconnected conductive film with sea-island structures (as evidenced in Fig. S5) dramatically hinders charge transport and collection (Fig. 6b). For further verification, a device was formed through an ex-situ two-step approach, i.e., a smooth polythioether film was prepared via photopolymerization for 30 min, followed by spincoating of the C8-BTBT/chloroform solution and subsequent thermal baking at 70 oC for 30 min (Fig. 6C). The ex-situ two-step prepared phototransistor exhibits better transistor characteristics as the calculated mobility and on/off ratio in dark are 1.0 × 10-1 cm2 V-1 s-1 and 1.5 × 105, separately, before UV light illumination, both are around one order of magnitude higher than the in-situ photopolymerized phototransistor (Fig. S19). The higher mobility and on/off ratio are due to the smoother interface. Nevertheless, the ex-situ two-step prepared device shows much slower photoresponse upon UV illumination, and higher channel current when the UV light is discontinued (Fig. S20). These results indicate that rougher interface generated from the in-situ photopolymerization favors exciton dissociation upon UV light exposure, and facilitates the charge carrier combination in dark.


Page 16 of 33

Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Proposed phase-separated structures and charges distribution. (a) Insitu

photopolymerized

blend

of

polythioether

and

C8-BTBT.

In-situ

photopolymerization-induced phase separation provided rich continuous mountain-like heterojunction interfaces for efficient exciton dissociation at the interface but a continuous conductive area for hole transport and collection above the interface. (b) In-situ thermally cured blend of polythioether and C8-BTBT. In-situ thermal curing led to sea-island structures, in which though rich heterojunction interfaces were created, the disconnected conductive film dramatically hindered charge transport and collection. (c) Ex-situ two-step cured polythioether/C8-BTBT blend. The continuous conductive area on the top facilitated hole transport and collection, but the smooth interface limited exciton dissociation thus afforded slower light response.

A fourth device was also prepared by thermally annealing the blend of poly(methyl methacrylate) (PMMA) and C8-BTBT.8 Surface topography and energy analyses confirm the vertical phase-separated structure of the thermally annealed PMMA/C8-BTBT blend (Fig. S21 and S22), in accordance with the vertical phaseseparated structure of the linear amorphous polymer/C8-BTBT blend directly observed by cross-section transmission electron microscopy.6 The 60 times larger mobility indicates the formation of a much smoother interface in the PMMA/C8-



Page 18 of 33

BTBT blend than in the photopolymerized phototransistor (Fig. S23), and a continuous conductive area for hole transport and collection on the top. Nevertheless, the 61 times lower light responsivity confirms the lack of efficient interface action for exciton dissociation (Fig. S24), which is expected to be primarily led by the smooth interface, though the electron trapping on PMMA surface may be much weaker than that on the polythioether surface. The broad adaptability to various substrates and low-temperature processing capability

of

photopolymerization

allow

for

facile

fabrication

of

flexible

phototransistors. Gold belts that served as gate electrodes were first deposited on a flexible and transparent poly(ethylene terephthalate) (PET) substrate through a shadow mask under vacuum, followed by vacuum deposition of a 30 nm thick Al2O3 layer that served as a dielectric by atomic layer deposition (ALD). To minimize the influence of Al2O3 on the device performance, a hexamethyldisilazane (HMDS) monolayer selfassembly was created on the upper surface of the Al2O3 layer under vacuum.34 A homogeneous solution of the monomers and C8-BTBT in chloroform was then spincoated on the self-assembled monolayer, followed by in-situ photopolymerization to generate the photopolymerized semiconductor blend. A 100 nm thick gold layer was finally deposited on the blend through a shadow mask under vacuum to create the source and drain electrodes (Fig. 7a).


Page 19 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Flexible phototransistors. (a) Schematic illustration on the structure of the flexible phototransistor. (b) Optical picture of the photopolymerized phototransistor arrays on a flexible and transparent PET substrate. (c) Light response of the photopolymerized phototransistor upon exposure to 4 mW cm-2 of 350 nm light at a VGS = 0 V and VDS = -10 V. A pulse of gate bias (VGS = -2 V and VDS = 0 V) was used to reset the device to the low conductivity state in dark.

The phototransistor arrays formed on the PET substrate exhibits good flexibility (Fig. 7b) and good UV-response performance (e.g., rise time of 12 s and decay time of 21 s, separately), upon exposure to 4 mW cm-2 of 350 nm light with application of a VDS of -10 V (Fig. 7c). When switching off the UV light, the IDS decreases and the low conductivity state could be reassumed by applying a small gate bias (VGS = -2 V, VDS = 0 V). Compared with the devices formed on rigid SiO2 coated wafer, the flexible devices show slightly inferior performance. One possible explanation is that the UV ozone treated SiO2 is more hydrophilic than the HMDS modified Al2O3, as evidenced by the water contact angle of 9o and 76o, respectively. The RMS for these interfaces are characterized to be 11.8 and 18.3 nm, separately. Nevertheless, the relatively low reset voltage (VDS = 0 V, VGS = -2 V) may promise the flexible phototransistors to be integrated into wearable devices. Employing high dielectric materials as the insulating layer is envisioned to afford lower reset voltage. These flexible phototransistors also present good repeat capability and comparative performance with the state-of-the-art UV photodetectors (Table 1). Table 1. Figure of merit of the state-of-the-art visible-bind UV photodetectors. Response material

Bias (V)

Iphoto (nA)

Idark (pA)

Iphoto/Idark ratio

Light intensity (mW cm-2)

Rise time (s)


Decay time (s)

Detectivity (Jones)

Responsivity (A W-1)

Ref


-30

C8-BTBT/

(rigid)

-2

polythioether

(flexible)

Page 20 of 33

5000

50

1.0 × 105

4.0

21

16

6.3 × 1014

2.5

this

200

10

2.0 × 104

4.0

12

21

5.6 × 1013

0.1

work

ZnO ultraporous nanoparticle network

2 × 10-4

440

1

3.3 × 105

8.6 × 10-5

250

150

1.5 × 1015

1.4 × 10-2

51

3DNH NiO/ZnO

1

3.4 × 105

18

1.9 × 106

8.0 × 10-5

5

9

3.0 × 1012

13

52

hybrid perovskites

15

5 × 106

1× 106

5 × 103

1.0 × 103

—

—

1.2 × 1010

4.7 × 10-2

53

p-Si/n-ZnO heterojunction

-2

9.6 × 104

3× 106

31.9

3.7 × 10-3

2 × 10-5

2 × 10-5

—

1.3 × 10-2

54

TiO2 nanowires

5

1.6

30

54

5.4 × 10-4

—

—

—

6.9 × 10-5

55

3C-SiC/ZnO nanowire

2

127.7

7 × 102

187.8

2.6 × 10-6

4 × 10-2

6 × 10-2

—

4.8 × 105

56

CONCLUSIONS In summary, we demonstrate a new protocol for constructing high performance UV-responsive phototransistors where the light responsive semiconductor layer is formed by in-situ photopolymerization-induced phase separation, as confirmed by evaluation of the surface energy and chemical composition. The results clearly demonstrate that the in-situ photopolymerization-induced phase separation not only provides a large amount of continuous mountain-like heterojunction interfaces between the cross-linked polythioether and C8-BTBT for efficient exciton dissociation at the interface, but also delivers a continuous conductive area for hole transport and collection above the interface, thus giving a light responsivity up to 2.5 A W-1, photocurrent/dark ratio of 5 orders of magnitude and normalized detectivity up to 6.3 × 1014 Jones, upon exposure to 4 mW cm-2 of 350 nm UV light (VGS = 0 V and VDS = 30 V). Moreover, the continuous mountain-like interface enables a fast light response. Flexile phototransistors have also been successfully fabricated on a PET substrate and


Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


characterized. This low-temperature, facile, and cost-effective photopolymerizationinduced

phase

separation

approach

offers

obvious

advantages

for

the

commercialization of low-cost, large-scale, flexible phototransistors that function as light detectors and photo-switching devices. Considering the broad materials availability, vast chemical versatility, and functionalization capability, this novel paradigm of in-situ photopolymerization-induced phase separation paves the way for construction of other high performance optoelectronic devices in which heterojunction interfaces are desired for efficient charge separation and charge carrier transport, and holds great promise to be integrated with low temperature processing such as printing, solvent processing and roll-to-roll fabrication. EXPERIMENTAL SECTION 1 Chemicals Trimethylolpropane tris(3-mercaptopropionate) (TMPTMP, purity: ≥ 95%), 1,3,5triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione

(TATATO,

purity:

98%),

diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO, purity: 97%), and 2,7dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT, purity: ≥ 99%) were purchased from Sigma-Aldrich. All chemicals were used as received without further purification. 2 Phototransistor fabrication All rigid bottom-gate/top-contact phototransistors were fabricated on heavily doped silicon wafers with a SiO2 layer (100 nm thick) on the top. The silicon wafer was sonicated in a DECON solution and rinsed with deionized water for twice, followed by drying (120 oC, 2 h) in an oven, finally was treated by UVO ozone. To fabricate flexible bottom-gate/top-contact phototransistors, gold belts served as gate electrodes (100 nm thick, 600 nm wide) were firstly deposited on a flexible and



Page 22 of 33

transparent PET substrate through a shadow mask, followed by vacuum deposition of a Al2O3 layer (30 nm thick) that served as a dielectric by ALD at the substrate temperature of 80 oC. Subsequently, hexamethyldisilazane (HMDS) was spin-cast above the Al2O3 layer under vacuum to form a monolayer self-assembly, and then baked (130

o

C, 30 min). Homogeneous solutions comprising stoichiometrically

equivalent TMPTMP and TATATO as monomers (2 mg mL-1), and TPO (0.04 mg mL-1) as the photoinitiator, and the p-type semiconductor C8-BTBT (3 mg mL-1) were prepared in chloroform and spin-cast on these substrates (2000 rpm, 40 s) in the Mbraun nitrogen glovebox. The concentration of C8-BTBT was controlled at 3 mg mL-1 for all solutions. Then, the samples were flood-cured by a 365 nm UV lamp (20 mW cm-2) for 30 min in the glovebox, creating semiconductor blends in-situ via photopolymerization-induced phase separation. Finally, 100 nm thick gold films were deposited (0.2 Å s-1) on the top surface of the photopolymerized semiconductor blends through a shadow mask (L/W = 50 µm/1000 µm) after vacuum evaporation (around 1 × 10-6 torr) in a chamber, which worked as source/drain electrodes in the phototransistors. For the thermally cured phototransistor and the PMMA-based transistor, the semiconductor layers were formed by putting the spin-cast samples on a hot plate (70 oC, 1 h) in the glovebox and then cooled down to room temperature. 3 Thickness measurement To characterize the thickness, thin films were formed on both silicon wafers without SiO2 and 100-nm thick SiO2 coated silicon. Thickness was measured by spectroscopic ellipsometry. Similar results were given for the identical sample on different substrates. The thickness for the neat C8-BTBT and polythioether was 21 and 20

nm,

respectively,

when

formed

independently.

The

thickness

of

the

photopolymerized semiconductor blend was tested to be 35 nm, while the thickness of


Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the bottom polythioether was measured to be 12 nm after the removal of C8-BTBT layer on the top, indicating that the thickness of C8-BTBT was around 23 nm on the top. 4 Electrical characterization The transfer characteristics and light response measurements were conducted on a Keithley 4200 Semiconductor Characterization System in air (humidity: 30% RH: 25 o

C), respectively. One portable UV lamp was used to illuminate the sample when

testing and the light intensity was determined to be around 4 mW cm-2 at 350 nm. The device reliability was confirmed by independent characterization of batches of devices at City University of Hong Kong and South University of Science and Technology of China (around 50 km far away from each other). 5 Surface characterization Contact angle, AFM and XPS measurements were conducted as reported elsewhere.34 The samples for XPS test were prepared on 100 nm thick gold-coated substrates to avoid the influence from the substrate. SEM images were characterized by a JEOL JSM-6335F field emission gun scanning electron microscope. 6 Crystal structures investigation Out-of-plane XRD patterns were recorded using a Bruker D2 Phaser X-ray benchtop diffractometer. Cu tube with 1.5184 Å was used as the tube. 7 Optical absorption Ground state absorptions of solid thin films spin-cast on transparent square quartz slides were characterized by a UV-1700 UV-vis spectrophotometer (Shimadzu). FT-IR absorptions of samples drop-cast on KBr plates were tested on a Fourier Transform Infra-Red Spectrometer (PE Spectrum 2000). 8 Emission properties



Emission spectra were recorded with the spectral mode on an Edinburgh Instruments LP920-KS spectrometer equipped with Princeton Instruments, PI-MAX3 intensified charge-coupled device (ICCD) and a Hamamatsu R928 photomultiplier tube (PMT) detector. The excitation source for the time-resolved emission was the third harmonic output (355 nm; 6-8 ns fwhm pulse width) of a Spectra-Physics Quanta-Ray Q-switched LAB-150 pulsed Nd:YAG laser (10 Hz).57 AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (X.Xie) and [email protected] (V.Roy) Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS We thank the financial support from the Young Scientists Project (51503045) and Key Program (51433002) of the National Natural Science Foundation of China, and the HK project (9440128, RGC T42-103/16-N). SUPPORTING INFORMATION Figure S1-S24 related to the characterizations for the thermally cured phototransistor, the photopolymerized phototransistor formed when changing the curing time and semiconductor content, and the PMMA/C8-BTBT phototransistor. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.

REFERENCES


Page 24 of 33

Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(1) Wang, C.; Liu, Z.; Li, M.; Xie, Y.; Li, B.; Wang, S.; Xue, S.; Peng, Q.; Chen, B.; Zhao, Z.; Li, Q.; Ge, Z.; Li, Z. The Marriage of AIE and Interface Engineering: Convenient Synthesis and Enhanced Photovoltaic Performance. Chem. Sci. 2017, 8, 3750-3758. (2) Dong, H.; Zhu, H.; Meng, Q.; Gong, X.; Hu, W. Organic Photoresponse Materials and Devices. Chem. Soc. Rev. 2012, 41, 1754-1808. (3) Jansen-van Vuuren, R. D.; Armin, A.; Pandey, A. K.; Burn, P. L.; Meredith, P. Organic Photodiodes: The Future of Full Color Detection and Image Sensing. Adv. Mater. 2016,

28, 4766-4802. (4) Granstrom, M.; Petritsch, K.; Arias, A. C.; Lux, A.; Andersson, M. R.; Friend, R. H. Laminated Fabrication of Polymeric Photovoltaic Diodes. Nature 1998, 395, 257-260. (5) Gong, X.; Tong, M.; Xia, Y.; Cai, W.; Moon, J. S.; Cao, Y.; Yu, G.; Shieh, C.-L.; Nilsson, B.; Heeger, A. J. High-Detectivity Polymer Photodetectors with Spectral Response from 300 nm to 1450 nm. Science 2009, 325, 1665-1667. (6) Yuan, Y.; Giri, G.; Ayzner, A. L.; Zoombelt, A. P.; Mannsfeld, S. C. B.; Chen, J.; Nordlund, D.; Toney, M. F.; Huang, J.; Bao, Z. Ultra-High Mobility Transparent Organic Thin Film Transistors Grown by an Off-Centre Spin-Coating Method. Nat. Commun. 2014, 5, 3005. (7) Smith, J.; Zhang, W.; Sougrat, R.; Zhao, K.; Li, R.; Cha, D.; Amassian, A.; Heeney, M.; McCulloch, I.; Anthopoulos, T. D. Solution-Processed Small Molecule-Polymer Blend Organic Thin-Film Transistors with Hole Mobility Greater Than 5 cm2/Vs. Adv. Mater. 2012, 24, 2441-2446. (8) Smithson, C. S.; Wu, Y.; Wigglesworth, T.; Zhu, S. A More Than Six Orders of Magnitude UV-Responsive Organic Field-Effect Transistor Utilizing a Benzothiophene Semiconductor and Disperse Red 1 for Enhanced Charge Separation. Adv. Mater. 2015,

27, 228-233.



Page 26 of 33

(9) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Click Chemistry: Diverse Chemical Function from a Few Good Reactions. Angew. Chem., Int. Ed. 2001, 40, 2004-2021. (10) Xi, W.; Pattanayak, S.; Wang, C.; Fairbanks, B.; Gong, T.; Wagner, J.; Kloxin, C. J.; Bowman,

C.

N.

Clickable

Nucleic

Acids:

Sequence-Controlled

Periodic

Copolymer/Oligomer Synthesis by Orthogonal Thiol-X Reactions. Angew. Chem., Int. Ed. 2015, 54, 14462-14467. (11) Lowe, A. B. Thiol-Ene "Click" Reactions and Recent Applications in Polymer and Materials Synthesis: A First Update. Polym. Chem. 2014, 5, 4820-4870. (12) Lowe, A. B. Thiol-Ene "Click" Reactions and Recent Applications in Polymer and Materials Synthesis. Polym. Chem. 2010, 1, 17-36. (13) Boyd, D. A. Sulfur and Its Role in Modern Materials Science. Angew. Chem., Int. Ed. 2016, 55, 15486-15502. (14) Hoyle, C. E.; Lowe, A. B.; Bowman, C. N. Thiol-Click Chemistry: A Multifaceted Toolbox for Small Molecule and Polymer Synthesis. Chem. Soc. Rev. 2010, 39, 13551387. (15) Xi, W.; Scott, T. F.; Kloxin, C. J.; Bowman, C. N. Click Chemistry in Materials Science.

Adv. Funct. Mater. 2014, 24, 2572-2590. (16) Gong, T.; Adzima, B. J.; Bowman, C. N. A Novel Copper Containing Photoinitiator, Copper(II) Acylphosphinate, and Its Application in Both the Photomediated CuAAC Reaction and in Atom Transfer Radical Polymerization. Chem. Commun. 2013, 49, 79507952. (17) Tasdelen, M. A.; Yilmaz, G.; Iskin, B.; Yagci, Y. Photoinduced Free Radical Promoted Copper(I)-Catalyzed Click Chemistry for Macromolecular Syntheses. Macromolecules 2012, 45, 56-61.


Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(18) Gong, T.; Adzima, B. J.; Baker, N. H.; Bowman, C. N. Photopolymerization Reactions Using the Photoinitiated Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) Reaction. Adv. Mater. 2013, 25, 2024-2028. (19) Peng, H. Y.; Wang, C.; Xi, W. X.; Kowalski, B. A.; Gong, T.; Xie, X. L.; Wang, W. T.; Nair, D. P.; McLeod, R. R.; Bowman, C. N. Facile Image Patterning Via Sequential Thiol-Michael/Thiol-Yne Click Reactions. Chem. Mater. 2014, 26, 6819-6826. (20) Peng, H. Y.; Nair, D. P.; Kowalski, B. A.; Xi, W. X.; Gong, T.; Wang, C.; Cole, M.; Cramer, N. B.; Xie, X. L.; McLeod, R. R.; Bowman, C. N. High Performance Graded Rainbow Holograms Via Two-Stage Sequential Orthogonal Thiol-Click Chemistry.

Macromolecules 2014, 47, 2306-2315. (21) Hoyle, C. E.; Bowman, C. N. Thiol-Ene Click Chemistry. Angew. Chem., Int. Ed. 2010,

49, 1540-1573. (22) Orski, S. V.; Poloukhtine, A. A.; Arumugam, S.; Mao, L. D.; Popik, V. V.; Locklin, J. High Density Orthogonal Surface Immobilization Via Photoactivated Copper-Free Click Chemistry. J. Am. Chem. Soc. 2010, 132, 11024-11026. (23) Adzima, B. J.; Tao, Y.; Kloxin, C. J.; DeForest, C. A.; Anseth, K. S.; Bowman, C. N. Spatial and Temporal Control of the Alkyne–Azide Cycloaddition by Photoinitiated Cu(II) Reduction. Nat. Chem. 2011, 3, 256-259. (24) DeForest, C. A.; Anseth, K. S. Photoreversible Patterning of Biomolecules within ClickBased Hydrogels. Angew. Chem., Int. Ed. 2012, 51, 1816-1819. (25) Gupta, N.; Lin, B. F.; Campos, L.; Dimitriou, M. D.; Hikita, S. T.; Treat, N. D.; Tirrell, M. V.; Clegg, D. O.; Kramer, E. J.; Hawker, C. J. A Versatile Approach to High-Throughput Microarrays Using Thiol-Ene Chemistry. Nat. Chem. 2010, 2, 138-145.



(26) Feng, W. Q.; Li, L. X.; Yang, C. W.; Welle, A.; Trapp, O.; Levkin, P. A. UV-Induced Tetrazole-Thiol Reaction for Polymer Conjugation and Surface Functionalization. Angew.

Chem., Int. Ed. 2015, 54, 8732-8735. (27) Bradley, L. C.; Stebe, K. J.; Lee, D. Clickable Janus Particles. J. Am. Chem. Soc. 2016,

138, 11437-11440. (28) Dondoni, A. The Emergence of Thiol–Ene Coupling as a Click Process for Materials and Bioorganic Chemistry. Angew. Chem., Int. Ed. 2008, 47, 8995-8997. (29) DeForest, C. A.; Polizzotti, B. D.; Anseth, K. S. Sequential Click Reactions for Synthesizing and Patterning Three-Dimensional Cell Microenvironments. Nat. Mater. 2009, 8, 659-664. (30) DeForest, C. A.; Anseth, K. S. Cytocompatible Click-Based Hydrogels with Dynamically Tunable Properties through Orthogonal Photoconjugation and Photocleavage Reactions.

Nat. Chem. 2011, 3, 925-931. (31) Guo, F. W.; Yang, B.; Yuan, Y. B.; Xiao, Z. G.; Dong, Q. F.; Bi, Y.; Huang, J. S. A Nanocomposite Ultraviolet Photodetector Based on Interfacial Trap-Controlled Charge Injection. Nat. Nanotechnol. 2012, 7, 798-802. (32) Han, S.-T.; Peng, H. Y.; Sun, Q. J.; Venkatesh, S.; Chung, K.-S.; Lau, S. C.; Zhou, Y.; Roy, V. A. L. An Overview of the Development of Flexible Sensors. Adv. Mater. 2017,

29, 1700375. (33) Yan, Y.; Huang, L.-B.; Zhou, Y.; Han, S.-T.; Zhou, L.; Zhuang, J.; Xu, Z.-X.; Roy, V. A. L. Self-Aligned, Full Solution Process Polymer Field-Effect Transistor on Flexible Substrates. Sci. Rep. 2015, 5, 15770. (34) Yan, Y.; Huang, L.-B.; Zhou, Y.; Han, S.-T.; Zhou, L.; Sun, Q. J.; Zhuang, J. Q.; Peng, H. Y.; Yan, H.; Roy, V. A. L. Surface Decoration on Polymeric Gate Dielectrics for Flexible


Page 28 of 33

Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Organic Field-Effect Transistors Via Hydroxylation and Subsequent Monolayer SelfAssembly. ACS Appl. Mater. Interfaces 2015, 7, 23464-23471. (35) Wang, H.; Liu, H.; Zhao, Q.; Cheng, C.; Hu, W.; Liu, Y. Three-Component Integrated Ultrathin Organic Photosensors for Plastic Optoelectronics. Adv. Mater. 2016, 28, 624630. (36) Zhang, H.; Hui, J.; Chen, H.; Chen, J.; Xu, W.; Shuai, Z.; Zhu, D.; Guo, X. Synergistic Photomodulation of Capacitive Coupling and Charge Separation toward Functional Organic Field-Effect Transistors with High Responsivity. Adv. Electron. Mater. 2015, 1, 1500159. (37) Guo, Y. L.; Yu, G.; Liu, Y. Q. Functional Organic Field-Effect Transistors. Adv. Mater. 2010, 22, 4427-4447. (38) Peng, H. Y.; Bi, S. G.; Ni, M. L.; Xie, X. L.; Liao, Y. G.; Zhou, X. P.; Xue, Z. G.; Zhu, J. T.; Wei, Y.; Bowman, C. N.; Mai, Y.-W. Monochromatic Visible Light “Photoinitibitor”: Janus-Faced Initiation and Inhibition for Storage of Colored 3D Images. J. Am. Chem.

Soc. 2014, 136, 8855-8858. (39) Peng, H. Y.; Chen, G. N.; Ni, M. L.; Yan, Y.; Zhuang, J. Q.; Roy, V. A. L.; Li, R. K. Y.; Xie, X. L. Classical Photopolymerization Kinetics, Exceptional Gelation, and Improved Diffraction Efficiency and Driving Voltage in Scaffolding Morphological H-PDLCs Afforded Using a Photoinitibitor. Polym. Chem. 2015, 6, 8259-8269. (40) Chen, G. N.; Ni, M. L.; Peng, H. Y.; Huang, F. H.; Liao, Y. G.; Wang, M. K.; Zhu, J. T.; Roy, V. A. L.; Xie, X. L. Photoinitiation and Inhibition under Monochromatic Green Light for Storage of Colored 3D Images in Holographic Polymer-Dispersed Liquid Crystals. ACS Appl. Mater. Interfaces 2017, 9, 1810-1819. (41) Ni, M. L.; Chen, G. N.; Sun, H. W.; Peng, H. Y.; Yang, Z. F.; Liao, Y. G.; Ye, Y. S.; Yang, Y. K.; Xie, X. L. Well-Structured Holographic Polymer Dispersed Liquid Crystals



by Employing Acrylamide and Doping Zns Nanoparticles. Mater. Chem. Front. 2017, 1, 294-303. (42) Penterman, R.; Klink, S. I.; de Koning, H.; Nisato, G.; Broer, D. J. Single-Substrate Liquid-Crystal Displays by Photo-Enforced Stratification. Nature 2002, 417, 55-58. (43) Minemawari, H.; Yamada, T.; Matsui, H.; Tsutsumi, J. y.; Haas, S.; Chiba, R.; Kumai, R.; Hasegawa, T. Inkjet Printing of Single-Crystal Films. Nature 2011, 475, 364-367. (44) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. Highly Soluble [1]Benzothieno[3,2-B]Benzothiophene (BTBT) Derivatives for HighPerformance, Solution-Processed Organic Field-Effect Transistors. J. Am. Chem. Soc. 2007, 129, 15732-15733. (45) Chu, Y.; Wu, X.; Lu, J.; Liu, D.; Du, J.; Zhang, G.; Huang, J. Photosensitive and Flexible Organic Field-Effect Transistors Based on Interface Trapping Effect and Their Application in 2D Imaging Array. Adv. Sci. 2016, 1500435. (46) Liu, C.; Minari, T.; Lu, X.; Kumatani, A.; Takimiya, K.; Tsukagoshi, K. SolutionProcessable Organic Single Crystals with Bandlike Transport in Field-Effect Transistors.

Adv. Mater. 2011, 23, 523-526. (47) Konstantatos, G.; Sargent, E. H. Nanostructured Materials for Photon Detection. Nat.

Nanotechnol. 2010, 5, 391-400. (48) Konstantatos, G.; Howard, I.; Fischer, A.; Hoogland, S.; Clifford, J.; Klem, E.; Levina, L.; Sargent, E. H. Ultrasensitive Solution-Cast Quantum Dot Photodetectors. Nature 2006,

442, 180-183. (49) Labastide, J. A.; Thompson, H. B.; Marques, S. R.; Colella, N. S.; Briseno, A. L.; Barnes, M. D. Directional Charge Separation in Isolated Organic Semiconductor Crystalline Nanowires. Nat. Commun. 2016, 7, 10629.


Page 30 of 33

Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(50) Li, M.; An, C.; Marszalek, T.; Baumgarten, M.; Müllen, K.; Pisula, W. Impact of Interfacial Microstructure on Charge Carrier Transport in Solution-Processed Conjugated Polymer Field-Effect Transistors. Adv. Mater. 2016, 28, 2245-2252. (51) Bo, R.; Nasiri, N.; Chen, H.; Caputo, D.; Fu, L.; Tricoli, A. Low-Voltage HighPerformance UV Photodetectors: An Interplay between Grain Boundaries and Debye Length. ACS Appl. Mater. Interfaces 2017, 9, 2606-2615. (52) Nasiri, N.; Bo, R.; Fu, L.; Tricoli, A. Three-Dimensional Nano-Heterojunction Networks: A Highly Performing Structure for Fast Visible-Blind UV Photodetectors. Nanoscale 2017, 9, 2059-2067. (53) Maculan, G.; Sheikh, A. D.; Abdelhady, A. L.; Saidaminov, M. I.; Haque, M. A.; Murali, B.; Alarousu, E.; Mohammed, O. F.; Wu, T.; Bakr, O. M. CH3NH3PbCl3 Single Crystals: Inverse Temperature Crystallization and Visible-Blind UV-Photodetector. J. Phys. Chem.

Lett. 2015, 6, 3781-3786. (54) Wang, Z.; Yu, R.; Wang, X.; Wu, W.; Wang, Z. L. Ultrafast Response P-Si/N-ZnO Heterojunction Ultraviolet Detector Based on Pyro-Phototronic Effect. Adv. Mater. 2016,

28, 6880-6886. (55) Tsai, T. Y.; Chang, S. J.; Weng, W. Y.; Hsu, C. L.; Wang, S. H.; Chiu, C. J.; Hsueh, T. J.; Chang, S. P. A Visible-Blind TiO2 Nanowire Photodetector. J. Electrochem. Soc. 2012,

159, J132-J135. (56) Zhang, X.; Liu, B.; Yang, W.; Jia, W.; Li, J.; Jiang, C.; Jiang, X. 3D-Branched Hierarchical 3C-SiC/ZnO Heterostructures for High-Performance Photodetectors.

Nanoscale 2016, 8, 17573-17580. (57) Chu, W.-K.; Ko, C.-C.; Chan, K.-C.; Yiu, S.-M.; Wong, F.-L.; Lee, C.-S.; Roy, V. A. L. A Simple Design for Strongly Emissive Sky-Blue Phosphorescent Neutral Rhenium



Complexes: Synthesis, Photophysics, and Electroluminescent Devices. Chem. Mater. 2014, 26, 2544-2550.


Page 32 of 33

Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC


Interface Engineering via Photopolymerization-Induced Phase

Recommend Documents