Brittle PCDTPT Based Elastic Hybrid Networks for Transparent Stretchable Skin‐Like Electronics

Organic semiconductors offer the opportunity to develop intrinsically stretchable skin‐like electronics for future applications. However, the lack of intrinsically stretchable materials is still a fundamental challenge, originating from the brittle nature of most organic semiconductors with the fracture strain at a few percent (<10%). Here, a stretchable semiconductor composite is reported by blending the brittle poly[4‐(4,4‐dihexadecyl‐4H‐cyclopenta[1,2‐b:5,4‐b′]dithiophen‐2‐yl)‐alt‐[1,2,5]thiad‐iazolo [3,4‐c] pyridine] (PCDTPT) semiconductor with the crack‐onset strain only at 5% and the styrene‐ethylene‐butylene‐styrene elastomer. This blend films present the increased crack‐onset strain up to 182% and superior optical transparency (>95% at 550 nm), with mobility as high as 2.31 cm2 V−1 s−1. The depth‐dependence light absorption spectra and the conductive atomic force microscopy images in horizontal and vertical directions of the blend film confirm the nonuniform distribution of PCDTPT fibers with sandwiched structure, which weakens the effect of device configuration on mobility. Compared with the conventional uniform film, the sandwiched film weakens the effect of device configuration on mobility. The fully transparent stretchable transistors with the blend films show the outstanding ductility and high optical transparency. This work opens up a feasible path for brittle organic semiconductors used in the transparent stretchable transistor, presenting their promising potential in future see‐through skin‐like electronics.

the original crack-onset strain higher than 20%. As we addressed above, the fracture strain of most polymer semiconductors is at a few percent. [21] If these brittle polymer semiconductors can be applied to prepare the all-stretchable OFETs, the flexible material selection will greatly push the development of high-performance intrinsically stretchable electronics.
Here, we demonstrate that a brittle polymer semiconductor, poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)alt- [1,2,5]thiadiazolo [3,4-c] pyridine] (PCDTPT) with the original crack-onset strain only at 5%, can be successfully combined with the styrene-ethylene-butylene-styrene (SEBS) elastomer, to achieve full-transparency intrinsically stretchable semiconductor material. The depth-dependence light absorption spectra and the conductive atomic force microscopy (AFM) images in horizontal and vertical directions of the blend film confirm the nonuniform distribution of PCDTPT fibers with a sandwiched structure, which weakens the effect of device configuration on mobility. The resulting blend semiconductor films exhibit charge mobility as high as 2.31 cm 2 V −1 s −1 , outstanding ductility up to 182%, superior optical transparency (>95% at 550 nm), and the fully stretchable devices show good conformability to the deforming human skin. These results provide new insight for utilizing versatile organic semiconductors for transparent stretchable skin-like electronic devices and help the researchers to consider the effect of the nonuniform component distribution on device performance for device design in stretchable electronics.

Results and Discussion
The stretchable semiconductor layers with high optical transparency were formed by directly spin-coating the blending solution with different PCDTPT/SEBS ratios, as shown in Figure 1a. When the amount of the PCDTPT polymer is reduced, the blend films could obtain high optical transparency in the visible spectra (400-700 nm), as shown in Figure 1b. Specifically, the blend film with the ratio of SEBS over 75 wt% presents the transmission of over 95% at 550 nm. Figure 1c shows a photo attached with a blended film with 75 wt% SEBS. The invisible film on the photo proves the good transparency of the PCDTPT/ SEBS film. This excellent optical transparency of the blend film renders them suitable for future invisible electronics. [33,34] As mentioned earlier, most of the active semiconductor polymers used in the current stretchable composite system possess stretchability with a crack-onset strain of over 20%. Here, a more brittle polymer with the crack-onset strain of 5% as the active semiconductor is shown to successfully achieve high stretchability. Figure 1d gives the previously reported crackonset strain of the semiconductor materials in intrinsically stretchable OFETs, including intrinsic polymer (open symbols), polymer/elastomer (filled symbols), polymer/small molecule (half-filled symbols). For comparison, the original crack-onset strain of the active semiconductors is also given in Figure 1d. For the stretchable OFETs, the most extensively used active semiconductor materials are DPP-based polymers, which generally present the original crack-onset strain of 20-110%. P3HT and IDT-BT, with the original crack-onset strain respectively at 30% and 97-130%, have also been used. In our work, the PCDTPT with the original crack-onset strain of 5% is combined with the elastic SEBS, and the obviously improved stretch capability up to 182% can be clearly seen in Figure 1d. This result indicates the outstanding mechanical performance of the material by blending the brittle organic semiconductor polymer and the elastomer. Due to the high elasticity, the film could obtain stable mechanical robustness, including poking, stretching, twisting, and crumpling ( Figure 1e). These encouraging results demonstrate the ability of the brittle semiconductor polymer to achieve transparent and stretchable material, which provides more choices for transparent stretchable skin-like electronics.
The optical images of the blend films with different SEBS contents at different degrees of strain are shown in Figure 2. The neat PCDTPT film presents the clear cracks at 5% strain, and the microcracks propagate could cross the whole film at 25% strain. Once we introduce SEBS into the semiconductor film, even with only 25% SEBS by weight, the ductility of the blend film is dramatically improved. And the ductility of films is improved with the increased amount of SEBS. The cracks of the blend polymer film with 25% SEBS by weight appear at 12% strain. The cracks of the blend film with 50% SEBS appear at 70% strain, indicating the crack-onset strain of four times higher than that of the blend film with 25% SEBS. It may be because the SEBS phase becomes the continuous phase, enabling the elastic modulus to drop significantly. [35] Elastomer SEBS could dissipate energy under stretching. More SEBS components are blended, better ductility and stretchability with the higher crack-onset strain of the blend semiconductor film we obtain. The crack-onset strain of the blend semiconductor film with 75% and 90% SEBS is observed at 120% and 182%, respectively. This indicates that the blend semiconductor film has achieved better ductility, which could be used in skin-like electronics.
To fully understand the effect of the blend ratio on the semiconductor films, detailed morphological, mechanical and electrical properties were studied. The morphology and Derjaguin, Muller, and Toropov (DMT) modulus mapping of the films were characterized by AFM. As shown in Figure 3a, the morphology of the PCDTPT/SEBS films reveals huge differences for different blend ratio. The neat PCDTPT film shows a smooth surface with a low surface roughness at 1.36 nm. Due to the high aggregation trend of PCDTPT polymer chains and the analogous surface energy of the two polymer components (PCDTPT and SEBS, Figure S1, Supporting Information), the hierarchical structure of PCDTPT was formed in the SEBS matrix. [35] When SEBS is 25% by weight, the PCDTPT network with the separated SEBS nanoparticles can be observed. With the increasing SEBS ratio, 1D nanofibers were formed (50 wt% SEBS). When SEBS reaches 75% by weight, longer PCDTPT nanofibers in the SEBS matrix could be observed in both AFM and DMT modulus images. This sudden change morphology may be due to the inhomogeneous distribution of the blend films and these similar results were also found in previous reports. [36] The PCDTPT nanofibers are invisible at 90% SEBS by weight, as a result of dramatically reduced PCDTPT content and increased SEBS content.
Stretchability, the fundamental property for skin-like electronics, facilitates retaining the electronic performance of devices under the mechanical deformation. Elastic modulus (E) of the blend films, [37] a critical parameter to characterize the stretchability, is defined as follows: E = ν A E A + ν B E B , where E A and E B respectively are the elastic modulus of SEBS and PCDTPT, and ν A and ν B are the volume fraction of SEBS and PCDTPT, respectively. According to the equation, the DMT modulus of the semiconductor films is related to the blend ratio of PCDTPT and SEBS. From the DMT mapping of Figure 3a, the average DMT modulus of the blend semiconductor film can be calculated and is given in Figure 3b. The average DMT modulus of the neat PCDTPT film is 637 MPa. The DMT modulus of the blend semiconductor films shows a monotonic decrease with the increasing weight ratio of the SEBS, suggesting the increased ductility and improved stretchability of the films.
When the ratios of SEBS were above 50%, the SEBS phase became the continuous phase, the blend film showed a significant drop in DMT modulus. During the weight ratio of SEBS is 75%, PCDTPT nanofibers dispersed in SEBS continuous phase with lower DMT modulus, Here the brighter region in height image is the PCDTPT nanofibers, which corresponds to the higher modulus in DMT mapping. And the DMT modulus of blend films decreases down to 148 MPa. In Figure 3c, the crack-onset strain of the blend films is increased with the increased weight ratio of SEBS, which is in good agreement with the change of the DMT modulus.
Further, we analyze the charge mobility of the blend films by fabricating FETs using the PCDTPT/SEBS layers. All the devices exhibit clear p-channel FET characteristics at room temperature in Figure S2 in the Supporting Information. The formation of the fiber-like network structure provides more efficient charge carrier transport for the blend films and hence better device performance. [32] As shown in Figure 3d, the mobility of the semiconductor film increases with the increasing ratio of SEBS from 0% to 75%. In particular, the PCDTPT/75% SEBS film shows the hole mobility of 2.31 cm 2 V −1 s −1 , which increases by 400% compared to that of the neat PCDTPT film. It is noticed that the mobility of the PCDTPT/SEBS decreases to 1 cm 2 V −1 s −1 when the SEBS content increases up to 90%, probably originating from the decreased interconnects of the conjugated polymer. Thus, the film with a fiber-like network at 75% SEBS reveals the highest charge mobility.
To investigate the vertical phase separation structure and composition change in vertical direction of the blend semiconductor film, the depth-dependence light absorption spectra were characterized. [38][39][40] Figure 4a gives the absorbed spectra of each sublayer of the blend film. With the increased etching time, the intensity of the characteristic absorption peak of PCDTPT located at 885 nm decreases sharply and then increases dramatically, suggesting that the PCDTPT molecules are preferably distributed in the top and bottom sublayers. Next, the conductive ability of the blend film respectively in horizontal and vertical directions was characterized by the tunneling conductive AFM. As shown in Figure 4b, Au electrodes were respectively connected with one side or the bottom of the semiconductor, and the surface conductive mapping was characterized by a conductive AFM tip. When the conductive ability of the film in a horizontal direction was measured, the bright wire-like conductive paths can be clearly observed in the top images of Figure 4b. The small fiber-like darker regions with a low current in the top surface of Figure 4b is the SEBS aggregation area, which is combined with the darker regions with lower DMT modulus in Figure 3a. The bright wire-like conductive paths in the top images of Figure 4b are the PCDTPT, which is higher regions with high DMT modulus and higher regions in AFM height image. These results confirm that the formation of fiberlike PCDTPT blend film networks in SEBS matrix is favorable for the formation of 1D conductive paths. In contrast, when the conductive ability of the film in the vertical direction was measured, only the separated high-conductivity points could be observed. The high conductive points are the PCDTPT distributed inside the film, which provides a conductive path in the vertical direction. This result suggests that only the located conductive filaments were formed in the vertical direction of the blend film. According to the depth-dependence light absorption spectra and conductive AFM images in Figure 4a  Based on a single blend semiconductor film, we fabricated the transistors with four types of device configuration, including top-gate top-contact (TGTC), bottom-gate bottomcontact (BGBC), bottom-gate top-contact (BGTC), and top-gate bottom-contact (TGBC), to show the effect of device configuration on the charge transport of our PCDTPT/SEBS OFETs. These devices were fabricated by a "separated preparation and layer-layer lamination" process as described in our previous report. [41] The gate electrode, source/drain electrodes in SEBS dielectric, and the PCDTPT/SEBS semiconductor layer were respectively prepared on rigid substrates and then were peeled and laminated together (details in Figure S4, Supporting Information). The device configuration and the corresponding electrical performance are shown in Figure 4d. It can be observed that the TGTC device presents the similar electrical properties to BGBC, and BGTC presents the similar electrical properties to TGBC devices, regardless of the top or bottom of the blend film nearer to the conductive channel. The off-state current of the BGTC and TGBC devices is higher than that of the TGTC and BGBC devices, while their mobilities only show a difference of ≈0.002 cm 2 V −1 s −1 . These results are different from the conventional uniform semiconductor film device.
In p-type organic transistors, accumulation of the charge carriers occurs at the semiconductor side near the insulator, typically under negative gate voltage, and the carriers are depleted under the sufficiently positive gate voltage with the low off-sate current. However, in our experiment, the blended semiconductor film presents a sandwich structure (Figure 4c). In this case, the low-conductivity interlayer of the blend film holds back the depletion of the carriers at the semiconductor side far from the dielectric. As a result, in BGTC and TGBC devices, the gate voltage effect is weakened, and the carriers can directly transport between the source and drain electrodes resulting in a higher off-state current. On the other hand, the conventional BGTC and TGBC devices with the uniform semiconductor film generally present higher mobilities than the TGTC and BGBC devices, originating from lower contact resistance. Here, however, the BGTC and TGBC devices require the current to cross the semiconductor thickness, and the sandwich structure of the blend semiconductor layer with the lowconductivity interlayer increases the access resistance of the transistor, resulting in their similar mobilities to the TGTC and BGBC devices. [42,43] Therefore, it can be concluded that the sandwiched semiconductor layer in the blend film weakens the effect of device configuration on mobility.
Further, we investigated the electrical properties of the PCDTPT/SEBS films under strain. The detailed experimental design is described in Figure 5a. The blend semiconductor film was peeled from the rigid substrate with the help of polydimethylsiloxane (PDMS), stretched to the desired stain, and then laminated on the Au electrodes on octadecyltrichlorosilane (OTS)-SiO 2 /Si substrates for the fabrication of FET devices. The PCDTPT/SEBS films with 75% SEBS are selected to investigate the charge mobility under strain, which present good stretchability and electrical performance. The typical transfer curves of the devices with different tensile strain values are shown in Figure 5b and Figure S5 in the Supporting Information, and the relationship between the electrical properties (mobility and drain current) and strain values is given in Figure 5c. The charge mobility of the PCDTPT/SEBS films decreases from 0.13 to 0.044 and 0.20 to 0.055 cm 2 V −1 s −1 when the strain increases from 0% to 100% in the direction parallel and perpendicular to the channel, respectively. Note that the mobility (µ 0 ) of the TFTs with the PCDTPT/SEBS films via a transfer-lamination process at 0% strain were lower than that of the TFTs based on spin-coated films on SiO 2 . The similar phenomenon can be observed in previous reports and can be ascribed to the possible deformation and mechanical damage in the mechanical peeling and adherence processes. [31,35] The blend film could retain electrical properties under large tensile strain. The normalized mobility (µ/µ 0 ) values of the FETs under strain are shown in Figure 5d. Compared with the unstretched film, the blend films under 100% strain respectively exhibited 0.34 and 0.28-fold changes in charge mobility in parallel and perpendicular to the channel direction. When the film is stretched at a typical strain that occurs in human body motion (25% strain), [18] the mobility is almost unchanged. This slight change in mobility is very favorable for the application of skin-like electronics.
Fully transparent and stretchable transistor devices were subsequently fabricated based on the optimized blend semiconductor films with 75% SEBS (Figure 6a). Photolithographic poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/single-wall carbon nanotube (SWCNT) patterns are used as electrodes, [44] and the SEBS is as dielectric. The peeled gate electrodes were successively laminated onto the dielectric and semiconductor layer and were laminated onto the peeled S/D electrodes to fabricate the fully transparent and stretchable transistors with the bottom-gate top-contact architecture (details in Figure S6, Supporting Information). The elastic electrodes service as both the supporting substrate and the encapsulation layer, which is favorable for the improved mechanical stretchability and tensile stability of the devices. Thanks to all the transparent components, the transistors exhibit good transparency, as displayed in the inset of Figure 6b, where the screen of the watch can be clearly seen through transistors (marked with white dash lines). Figure 6b shows the transmittance of the transistors is 87.3% at the wavelength of 550 nm. Figure 6c exhibits the transparent and stretchable FETs adhered onto a moving wrist, showing the application potential in the transparent and stretchable electronics. Due to the outstanding stretchability and transparency, the FETs still remain intimate adherence with the moving of the wrist and the skin could be clearly seen through the devices.
To investigate the electrical characteristics and stretchability of the fully transparent and stretchable transistor devices, we have systematically tested the devices under different strain. The transfer and output curves of the FETs are shown in Figure 6d, presenting the p-type field-effect characteristics. The devices give the average and highest field-effect mobilities (µ) of 0.075 and 0.13 cm 2 V −1 s −1 , respectively. The electrical performance of the fully transparent and stretchable FETs at different strains parallel (left) and perpendicular (right) to the channel direction are shown in Figure 6e and Figure S7 in the Supporting Information. Both the device's geometry and the dielectric capacitance were changed under strain, which affected the electronic performance (Table S2, Supporting Information). As described above, the most common strain in human body motion is below 25%. In Figure 6e, the fully transparent and stretchable transistors under 25% strain exhibit 0.13-fold change in mobility and 0.46-fold change in on-state current relative to that of 0% strain in the parallel direction. In the perpendicular direction, the mobility and on-current of the devices under 25% strain exhibit 0.23 and 0.35-fold decrease compared with those at 0% strain. All these results indicate that the fully transparent and stretchable transistors possess excellent electrical and mechanical properties, which shows the huge potential for next-generation transparent and stretchable skin-like electronics.
In addition to the brittle PCDTPT polymers, the same blend method can be applied to the well-known n-type polymer semiconductor P(NDI2OD-T2) (N2200). [45] The chemical molecular structure of N2200 is shown in Figure 7a. The changes of the blend N2200/SEBS films in electrical and mechanical performance are shown in Figure 7b (transfer curves see Figure S10, Supporting Information). The neat N2200 also presents the brittle nature with a crack-onset strain of only 3%. Figure 7c shows the AFM images and DMT modulus mapping of the N2200/SEBS. The fiber-like structures are gradually formed with the increased SEBS content (Figure 7c), which provides more efficient charge carrier transport (Figure 7b). In Figure 7c, the DMT modulus of the blend films is decreased with the increasing weight ratio of SEBS. The lower DMT modulus offers the higher ductility and stretchability of the N2200/ SEBS blend films, which can be confirmed by Figure 7b. The optical microscopy images in Figure 7d show the gradually decreased number of cracks at 100% strain with the increasing blend ratios of SEBS. The mobility of the N2200/SEBS blend films increases with the increased ratios of the SEBS from 0% to 75%, as shown in Figure 7b. The N2200/SEBS film with 90% SEBS still has fiber-like network structure in AFM height image. However, the N2200/SEBS film with 90% SEBS contains significant amounts of insulated SEBS elastomer, thereby meaning that the connectivity is may not good between the fibers, and eventually causing the lower electrical performance. The trend is fully consistent with our results in the PCDTP/ SEBS blend films. The mobility is up to 0.1 cm 2 V −1 s −1 based on the N2200/75% SEBS. These results suggest that good stretchability and high mobility can be obtained by blending the brittle N2200 and the elastic SEBS.

Conclusion
In this paper, based on a brittle PCDTPT polymer semiconductor with the original crack-onset strain only at 5%, we demon strate a high-transparency stretchable semiconductor film with hybrid structures of elastomer-polymer networks. The blend weight ratio directly affects the transparency, morphology, Figure 6. Fabrication, optical, electrical, and mechanical properties of the fully transparent stretchable transistor. a) Fabrication scheme of the device via lamination method. b) Transmittance spectra. Inset is the optical photograph of transistors adhered on a watch screen. c) Transistors adhered on the moving wrist to show the conformability, transparency, and stretchability. d) Typical transfer and output curves. e) Changes in the normalized mobility and drain current during stretching to 100% strain parallel (left) and perpendicular (right) to the channel direction (µ 0 is the average mobility of fully transparent stretchable transistor at 0% strain). and elastic modulus of the material and hence affects the optical transmittance, mechanical ductility, and mobility. The PCDTPT/SEBS network films with 75% SEBS present a high transmittance of over 95% at 550 nm and a high crack-onset strain at 120% strain. The PCDTPT/SEBS blend system offers higher mobility than the neat PCDTPT film because of the formation of nanofiber structures. The highest mobility up to 2.31 cm 2 V −1 s −1 can be obtained from the blend film with 75% SEBS. The depth-dependence light absorption spectra and the conductive AFM images in horizontal and vertical directions of the blend film, confirmed the PCDTPT fibers are preferably distributed in the top and bottom sublayer, and the conductivity capability of the blend film in the vertical direction is decreased, which weakens the effect of device configuration on mobility. Further, fully transparent and stretchable transistors using the high transparent, stretchable and high-mobility PCDTPT/SEBS films were fabricated. The resulting transistors present intimate adherence to the moving human skin, high transmittance of 87.3% at the wavelength of 550 nm, and significant stability of electrical performance under the strains. Our results provide scientific insights for the application possibility of most polymer semiconductors into the transparency and stretchability of blend systems and a pathway toward future see-through skin-like electronic devices and systems.

Experimental Section
Materials: PCDTPT and N2200 were purchased from 1-material and Sigma-Aldrich, respectively. SEBS H1221 and H1052 were purchased from the Asahi Kasei company. SEBS H1221 and H1052 were used as an elastomer that was mixed with PCDTPT and dielectric layer, respectively. PDMS (Sylgard 184) and OTS were provided by DowCorning and Acros Corporation, respectively. The solvents used here, including 1,2-chlorobenzene, toluene, and acetone, surface active agent (Capstone FS-30), and ethylene glycol, were purchased from Sigma-Aldrich. PEDOT:PSS aqueous solution (Clevios PH1000) and SWCNT aqueous dispersion with the initial concentration of 0.22 mg mL −1 (purity of >95 wt%) were purchased from Heraeus and Chengdu Organic Chemicals Co. Ltd., Chinese Academy of Sciences, Figure 7. Mechanical and electrical performance of N2200/SEBS blend films with different SEBS content. a) Chemical molecular structure of N2200. b) Mobility, DMT modulus, and crack-onset strain. c) AFM height images and DMT modulus mapping. d) Optical microscope images respectively under 0% and 100% strain. Scale bar: 20 µm.
respectively. All of the above materials were used as received without any purification.
Preparation and Characterization of the Blend Semiconductor Films: The semiconductor with different SEBS contents were dissolved in 1,2-chlorobenzene with the concentration of 15 (PCDTPT) and 10 (N2200) mg mL −1 , respectively. All the solutions were stirred over the night before use. The PCDTPT/SEBS and N2200/SEBS solutions spin-coated on OTS-modified SiO 2 at 6000 and 4000 rpm for 1 min, respectively. Then the films were annealed at 150 °C for 30 min under nitrogen atmosphere. The blend films were transferred onto PDMS films (crosslinking ratio of 12:1) for obtaining stretchable and transparent properties. The images of AFM were measured by a Dimension Icon instrument (Bruker) in air. The crack-onset strain and transparency of the networks film were measured by Olympus Microscope (BX51) and UV−vis spectroscopy in transmission mode (UH4150, Hitachi), respectively. To get the film-depth-dependent sublayer absorption spectrum, the same blend semiconductor film was incrementally etch the film from top to bottom, and the absorption spectra of the film were performed. The method is detailed description in previous reports. [38] Electrical Characterization of the Blend Semiconductor Films: The 20 nm gold source/drain electrodes were deposited onto the OTSmodified SiO 2 by thermal evaporation with a shadow mask (channel length (L) and width (W) of 200 and 1000 µm). i) The polymer solutions were directly spun on the OTS-SiO 2 with gold electrodes, and then the films were annealed at 150 °C for 30 min under nitrogen atmosphere. These BGTC devices were used to characterize the mobility of the elastomer-polymer networks films with different SEBS contents. ii) To study the structure of the elastomer-polymer networks films, the devices with TGTC, BGBC, BGTC, and TGBC architectures were fabricated based on a single blend semiconductor film. The PDMS was directly spun on the Au electrodes. The films mentioned above were annealed at 70 °C for 1 h to obtain the PDMS film with gate electrodes embedded internally. The SEBS H1052 solution (60 mg mL −1 , toluene) spun on Au S/D electrodes to obtain S/D electrodes and dielectric layers. All the fabrication processes of the transistors were shown in Figure S4 in the Supporting Information. iii) To obtain the mobility of the devices under different deformations, the elastomer-polymer networks films transferred on PDMS were laminated on the OTS-SiO 2 with gold electrodes. The electrical characteristics of organic fieldeffect transistor devices were recorded with a Keithley 4200-SCS and a Cascade M150 probe station in a clean and shielded box at room temperature in the air. All the field-effect mobility was extracted from the transfer characteristics in saturated regime with the standard equation: Fabrication and Characterization of Transparent and Stretchable Transistor: The stretchable PEDOT:PSS/SWCNT electrodes were fabricated according to the photolithography process as was reported recently. [44] The PDMS was directly spun on the electrodes. The films mentioned above were annealed at 70 °C for 1 h to obtain the PDMS film with electrodes embedded internally. The dielectric layer was obtained by spin coating SEBS H1052 solution (60 mg mL −1 , toluene) onto OTS-Si at 1000 rpm for 1 min. The dielectric layer was annealed at 80 °C for 2 h in air for removing the toluene, and the thickness of the SEBS dielectric film was 2 µm. All the fabrication processes of the transparent and stretchable transistor were shown in Figure S6 in the Supporting Information. The dielectric constant of SEBS dielectric layer is ≈2.91 and the capacitance was calculated using the thickness of the stretched film under different strains (Table S2, Supporting Information).

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.