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, 5 (11), 1884-1891

Stretchable and Fully Degradable Semiconductors for Transient Electronics


Stretchable and Fully Degradable Semiconductors for Transient Electronics

Helen Tran et al. ACS Cent Sci.


The next materials challenge in organic stretchable electronics is the development of a fully degradable semiconductor that maintains stable electrical performance under strain. Herein, we decouple the design of stretchability and transience by harmonizing polymer physics principles and molecular design in order to demonstrate for the first time a material that simultaneously possesses three disparate attributes: semiconductivity, intrinsic stretchability, and full degradability. We show that we can design acid-labile semiconducting polymers to appropriately phase segregate within a biodegradable elastomer, yielding semiconducting nanofibers that concurrently enable controlled transience and strain-independent transistor mobilities. Along with the future development of suitable conductors and device integration advances, we anticipate that these materials could be used to build fully biodegradable diagnostic or therapeutic devices that reside inside the body temporarily, or environmental monitors that are placed in the field and break down when they are no longer needed. This fully degradable semiconductor represents a promising advance toward developing multifunctional materials for skin-inspired electronic devices that can address previously inaccessible challenges and in turn create new technologies.

Conflict of interest statement

The authors declare no competing financial interest.


Figure 1
Figure 1
Design of fully degradable semiconducting polymer films through the nanoconfinement effect. (a) Illustration of the dual characteristics, stretchability and full degradability, of the semiconductor designed herein enables its application in transient devices on dynamic surfaces. (b) Illustration of nanoconfined acid-labile semiconductor fibers embedded within a biodegradable elastomer. (c) Chemical structure of the biodegradable elastomer based on polycaprolactone, E-PCL, and the known degradation pathway of PCL. (d) Chemical structure of the fully degradable semiconducting polymer, p(DPP-PPD), and the monomeric byproducts after initial cleavage. Three side-chain designs vary in the alkyl length: C1–C8C10 (top), C1–C10C12 (middle), and C4–C10C12 (bottom).
Figure 2
Figure 2
Morphological characterization. (a) Stress–strain curves of E-PCL show stretchability above 1000% strain. Insets show photographs of the elastomer during testing. (b) Ten cycles of stress–strain curves of E-PCL at 30% strain show minor hysteresis upon repeated stretching cycles. (c) Photographs of a film of nanoconfined p(DPP-PPD) transferred to PDMS that was stretched to 100%. (d) Normalized by the semiconductor content, the integrated intensity of the (200) peak extracted from GIWAXS decreases upon nanoconfinement. The inset shows a sample GIWAXS spectra. (e) The change in dichroic ratio upon strain for nanoconfined p(DPP-PPD) is linear, unlike neat p(DPP-PPD), indicating alignment without the formation of thin-film cracks. (f) Bright field images of stretched nanoconfined p(DPP-PPD) strain show a uniform blue thin film, whereas neat p(DPP-PPD) shows cracks. (g) Polarized optical images of nanoconfined p(DPP-DPP) show birefringence along the direction of strain (indicated by top left arrows). (h) Atomic force microscopy images of nanoconfined p(DPP-PPD) at 0% (top) and 100% (bottom) strain. (i) X-ray photoelectron spectroscopy along the depth of the thin film shows a higher sulfur content (sulfur is only present in the semiconductor) at the top and bottom interfaces, as illustrated in the 3D model.
Figure 3
Figure 3
Electrical performance comparison of neat and nanoconfined p(DPP-PDD). (a) A typical transfer curve (VDS = −30 V) of neat p(DPP-PPD) at 0% strain is shown (dashed lines, square root of the drain current; gray lines, IGS). (b) A typical transfer curve (VDS = −30 V) of nanoconfined p(DPP-PPD) at 0% strain is shown (dashed lines, square root of the drain current; gray lines, IGS). (c) The mobility of an FET device of neat and nanoconfined p(DPP-PPD) at different E-PCL content percentages. The insets show AFM images corresponding to 10%, 60%, and 90% E-PCL. (d) Illustration of the device structure for characterizing films under strain feature a layer of SEBS to ensure uniform large-area transfer. (e, f) The change in saturation mobility of neat and nanoconfined p(DPP-PPD) during stretching to 100% strain is shown, both parallel (e) and perpendicular to (f) the charge transport direction.
Figure 4
Figure 4
Degradation and biocompatibility characterization of neat and nanoconfined p(DPP-PDD). (a) The weight loss percentage of E-PCL films show degradation with time on the length scale of days. (b) UV–vis absorption spectra of a solution of p(DPP-PPD) in chlorobenzene with the addition of 1% 1 M TFA decreases with time and eventually is negligible by day 40. Inset shows the evolution of color during degradation. (c) The normalized peak maxima extracted from UV–vis absorption spectra of a thin film of neat and nanoconfined p(DPP-PPD) in 1 M TFA water show a gradual decrease with time. The maxima are eventually negligible by day 10. (d) Cell viability for glass with ethanol (negative control), E-PCL, neat p(DPP-PPD), and nanoconfined p(DPP-PPD). (e) Fluorescence images of human embryonic kidney (HEK) 293 cells seeded on the different substrates. The green fluorescence arises from calcein-AM staining of intact cytoplasm. The red fluorescence arises from ethidium homodimer-1 (EthD-1), which is a cell-impermeant nuclear stain. Cells seeded on E-PCL, neat p(DPP-PPD), and nanoconfined p(DPP-PPD) show high cell viability and do not show characteristic red fluorescence indicative of cell death.

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