Highly stretchable organic electrochemical transistors with strain-resistant performance.

Realizing fully stretchable electronic materials is central to advancing new types of mechanically agile and skin-integrable optoelectronic device technologies. Here we demonstrate a materials design concept combining an organic semiconductor film with a honeycomb porous structure with biaxially prestretched platform that enables high-performance organic electrochemical transistors with a charge transport stability over 30-140% tensional strain, limited only by metal contact fatigue. The prestretched honeycomb semiconductor channel of donor-acceptor polymer poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-diketo-pyrrolopyrrole-alt-2,5-bis(3-triethyleneglycoloxy-thiophen-2-yl) exhibits high ion uptake and completely stable electrochemical and mechanical properties over 1,500 redox cycles with 104 stretching cycles under 30% strain. Invariant electrocardiogram recording cycles and synapse responses under varying strains, along with mechanical finite element analysis, underscore that the present stretchable organic electrochemical transistor design strategy is suitable for diverse applications requiring stable signal output under deformation with low power dissipation and mechanical robustness.

Ultranarrow Bandgap Naphthalenediimide-Dialkylbifuran-Based Copolymers with High-Performance Organic Thin-Film Transistors and All-Polymer Solar Cells.

A new polymer acceptor poly{(N,N'-bis(2-ethylhexyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl)-alt-5,5-(3,3'-didodecyl-2,2'-bifuran)} (NDI-BFR) made from naphthalenediimide (NDI) and furan-derived head-to-head-linked 3,3'-dialkyl-2,2'-bifuran (BFR) units is reported in this study. Compared to the benchmark polymer poly(naphthalenediimide-alt-bithiophene) (N2200), NDI-BFR exhibits a larger bathochromic shift of absorption maxima (842 nm) with a much higher absorption coefficient (7.2 × 104 m-1 cm-1 ), leading to an ultranarrow optical bandgap of 1.26 eV. Such properties ensure good harvesting of solar light from visible to the near-infrared region in solar cells. Density functional theory calculation reveals that the polymer acceptor NDI-BFR possesses a higher degree of backbone planarity versus the polymer N2200. The polymer NDI-BFR exhibits a decent electron mobility of 0.45 cm2 V-1 s-1 in organic thin-film transistors (OTFTs), and NDI-BFR-based all-polymer solar cells (all-PSCs) achieve a power conversion efficiency (PCE) of 4.39% with a very small energy loss of 0.45 eV by using the environmentally friendly solvent 1,2,4-trimethylbenzene. These results demonstrate that incorporating head-to-head-linked BFR units in the polymer backbone can lead to increased planarity of the polymer backbone, reduced optical bandgap, and improved light absorbing. The study offers useful guidelines for constructing n-type polymers with narrow optical bandgaps.

Fused Bithiophene Imide Oligomer and Diketopyrrolopyrrole Copolymers for n-Type Thin-Film Transistors.

Diketopyrrolopyrrole (DPP)-based copolymers have received considerable attention as promising semiconducting materials for high-performance organic thin-film transistors (OTFTs). However, these polymers typically exhibit p-type or ambipolar charge-transporting characteristics in OTFTs due to their high-lying highest occupied molecular orbital (HOMO) energy levels. In this work, a new series of DPP-based n-type polymers have been developed by incorporating fused bithiophene imide oligomers (BTIn) into DPP polymers. The resulting copolymers BTIn-DPP show narrow band gaps as low as 1.27 eV and gradually down-shifted frontier molecular orbital energy levels upon the increment of imide group number. Benefiting from the coplanar backbone conformation, well-delocalized π-system, and favorable polymer chain packing, the optimal polymer in the series shows promising n-type charge transport with an electron mobility up to 0.48 cm2 V-1 s-1 in OTFTs, which is among the highest values for the DPP-based n-type polymers reported to date. The results demonstrate that incorporating fused bithiophene imide oligomers into polymers can serve as a promising strategy for constructing high-performance n-type polymeric semiconductors.

Dialkoxybithiazole: a new building block for head-to-head polymer semiconductors.

Polymer semiconductors have received great attention for organic electronics due to the low fabrication cost offered by solution-based printing techniques. To enable the desired solubility/processability and carrier mobility, polymers are functionalized with hydrocarbon chains by strategically manipulating the alkylation patterns. Note that head-to-head (HH) linkages have traditionally been avoided because the induced backbone torsion leads to poor π-π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4'-dialkoxy-5,5'-bithiazole (BTzOR), and its incorporation into polymers for high performance organic thin-film transistors. The small oxygen van der Waals radius and intramolecular S(thiazolyl)···O(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40-1.63 eV), and high crystallinity. In comparison to previously reported 3,3'-dialkoxy-2,2'-bithiophene (BTOR), BTzOR is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)C-H with (thiazole)N reduces steric encumbrance in -BTzOR-Ar- dyads by eliminating repulsive C-H···H-C interactions with neighboring arene units, thereby enhancing π-π overlap and film crystallinity; and (b) thiazole electron-deficiency compensates alkoxy electron-donating characteristics, thereby lowering the BTzOR polymer HOMO versus that of the BTOR analogues. Thus, the new BTzOR polymers show substantial hole mobilities (0.06-0.25 cm(2)/(V s)) in organic thin-film transistors, as well as enhanced I(on):I(off) ratios and greater ambient stability than the BTOR analogues. These geometric and electronic properties make BTzOR a promising building block for new classes of polymer semiconductors, and the synthetic route to BTzOR reported here should be adaptable to many other bithiazole-based building blocks.

Bithiophene imide and benzodithiophene copolymers for efficient inverted polymer solar cells.

Bithiophene imide (BTI) and benzodithiophene (BDT) copolymers are synthesized for application in organic photovoltaic (OPV) cells. The electron deficiency of the BTI units leads to polymers with a low-lying HOMOs (∼-5.6 eV). Inverted solar cells are fabricated to investigate the OPV performance of the BTI-based polymers and achieve power conversion efficiencies up to 5.5%, with substantial V(oc)s above 0.9 V which are among the highest V(oc)s reported to date for polymer/PCBM solar cells. The results indicate that the BTI is a promising building block for constructing polymer donors for OPV applications.