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Natural soft tissue achieves a rich variety of functionality through a hierarchy of molecular, microscale, and mesoscale structures and ordering. Inspired by such architectures, we introduce a soft, multifunctional composite capable of a unique combination of sensing, mechanically robust electronic connectivity, and active shape morphing. The material is composed of a compliant and deformable liquid crystal elastomer (LCE) matrix that can achieve macroscopic shape change through a liquid crystal phase transition. The matrix is dispersed with liquid metal (LM) microparticles that are used to tailor the thermal and electrical conductivity of the LCE without detrimentally altering its mechanical or shape-morphing properties. Demonstrations of this composite for sensing, actuation, circuitry, and soft robot locomotion suggest the potential for versatile, tissue-like multifunctionality.

comprised of a conjugated polymer as the electron donor and a fullerene derivative as the electron acceptor. [2,3] Conventional fullerene acceptors like [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) may be unfavorable for practical application, due to the inefficient absorption in visible and near-infrared (IR) regions, fixed molecular structure, complex purification process, and other complications well-documented in the literature. [4][5][6][7][8] In addition, the morphology of polymer-fullerene blends is very sensitive to thermal annealing, solvent additive, film thickness, and especially D:A ratio, resulting in significantly different device performance. [9][10][11] Recently, people have shown that the integration of either polymeric or molecular acceptor into photovoltaic devices would be advantageous. The chemical structures of nonfullerene acceptor can be easily adjusted to tune their energy levels, and the conjugated molecule or polymer acceptor demonstrates enhanced absorption at long wavelengths relative to fullerenes. [12] Thus nonfullerene photovoltaics can have improved harvest of solar radiation, enhanced thermal and mechanical stability, and reduced open-circuit voltage loss. [13] To date, solution-processed nonfullerene solar cells based on polymer-polymer (all-polymer) and polymer-small molecule blend have achieved power conversion efficiencies (PCEs) of 10% and 13%, respectively. [14][15][16][17][18][19] Exciton dissociation and charge transport are at the core of organic photovoltaics, which is strongly affected by the BHJ blend morphology. [20][21][22][23] In fullerene-based systems, the morphology of thin films is critical to the device performance and has been extensively studied. [24] How the blend morphology of nonfullerene blend affects device efficiency and stability is of growing interest as the PCEs of many nonfullerene solar cells now exceed the best fullerene devices. It is well known that the morphology has been largely influenced by the D:A blend ratio. Early studies on fullerene-based devices observed a drastic change in film morphology when fabricating the devices with increased acceptor content. [25][26][27][28] However, for nonfullerene solar cells, recent efforts mainly focus on materials synthesis and device optimization. To the best of our knowledge, systematical study on the effect of blend ratio on the device morphology, performance, and stability has not been reported, while it is of great importance to help achieve in-depth Tuning the blend composition is an essential step to optimize the power conversion efficiency (PCE) of organic bulk heterojunction (BHJ) solar cells. PCEs from devices of unoptimized donor:acceptor (D:A) weight ratio are generally significantly lower than optimized devices. Here, two high-performance organic nonfullerene BHJ blends PBDB-T:ITIC and PBDB-T:N2200 are adopted to investigate the effect of blend ratio on device performance. It is found that the PCEs of polymer-polymer (PBDB-T:N2200) blend are more tolerant to composition changes, relati...

Nanofibers (NFs) of the prototype conjugated polymer, poly(3-hexylthiophene) (P3HT), displaying H- and J-aggregate character are studied using temperature- and pressure-dependent photoluminescence (PL) spectroscopy. Single J-aggregate NF spectra show a decrease of the 0-0/0-1 vibronic intensity ratio from ~2.0 at 300 K to ~1.3 at 4 K. Temperature-dependent PL line shape parameters (i.e., 0-0 energies and 0-0/0-1 intensity ratios) undergo an abrupt change in the range of ~110-130 K suggesting a change in NF chain packing. Pressure-dependent PL lifetimes also show increased contributions from an instrument-limited decay component which is attributed to greater torsional disorder of the P3HT backbone upon decreasing NF volume. It is proposed that the P3HT alkyl side groups change their packing arrangement from a type I to type II configuration causing a decrease in J-aggregate character (lower intrachain order) in both temperature- and pressure-dependent PL spectra. Chain packing dependent exciton and polaron relaxation and recombination dynamics in NF aggregates are next studied using transient absorption spectroscopy (TAS). TAS data reveal faster polaron recombination dynamics in H-type P3HT NFs indicative of interchain delocalization whereas J-type NFs exhibit delayed recombination suggesting that polarons (in addition to excitons) are more delocalized along individual chains. Both time-resolved and steady-state spectra confirm that excitons and polarons in J-type NFs are predominantly intrachain in nature that can acquire interchain character with small structural (chain packing) perturbations.

absorption spectra extending to the NIR region have been designed and applied to the fabrication of OSCs. [6][7][8] A critical challenge arises as one decreases optical bandgaps (E g opt ) with respect to simultaneously achieving a high external quantum efficiency (EQE) and high open-circuit voltage (V OC ). [9] This challenge is due to the counterbalance between the driving force for charge separation, which aids in photocurrent generation, and voltage loss in the cell. [10,11] Finding ways to maximize V OC requires one to reduce the energy loss (E loss = E g opt -eV OC ) that occurs as a result of the multiple states that follow exciton generation. [12] Narrow bandgap (NBG) non-fullerene acceptors (NFAs) have emerged as the next generation of electron acceptors in OSCs. [13][14][15][16][17][18] Tunability of E g opt through molecular design allows one to tailor NIR absorption characteristics. [19,20] Considering that the maximum human photopic sensitivity is 555 nm and the maximum human scotopic sensitivity is 507 nm, [21] transparent photoactive materials should predominantly absorb solar radiation from ≈650 nm into the NIR region for semitransparent solar cell applications. In addition, since ≈50% of solar radiation intensity is in the NIR region, the development of NBG-NFAs with E g opt below ≈1.35 eV is desirable to effectively harvest solar NIR radiation. [1] Another encouraging feature of NFAs is that the energetic offsets that drive charge generation are small (<0.3 eV), [18,[22][23][24] which is beneficial for maintaining low E loss . Despite these desirable features, there has been less consideration for designing NBG-NFAs for transparent/NIR absorbing OSC applications. To address this challenge and expand the design of NIR harvesting acceptor molecules, we demonstrate in this contribution a new molecular design for ultra NBG-NFA materials with strong NIR response and small E loss .The two NBG NFAs described in this contribution are COTIC-4F and SiOTIC-4F (Figure 1a). Their molecular design includes incorporation of a cyclopentadithiophene (CPDT), or dithienosilole (DTS), unit as the central donor (D) fragment, which is flanked by two alkoxythienyl units (D′) to form an electron-rich D′-D-D′ central core. The D′-D-D′ units are end-capped with Two narrow bandgap non-fullerene acceptors (NBG-NFAs), namely, COTIC-4F and SiOTIC-4F, are designed and synthesized for the fabrication of efficient near-infrared organic solar cells (OSCs). The chemical structures of the NBG-NFAs contain a D′-D-D′ electron-rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end-capped with the highly electron-deficient unit 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (A), ultimately providing a A-D′-D-D′-A molecularconfiguration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (E g opt ) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk-he...