We studied the insulator-metal transition (IMT) in single-domain, single crystalline vanadium dioxide (VO(2)) microbeams with infrared microspectroscopy. The unique nature of such samples allowed us to probe the intrinsic behavior of both insulating and metallic phases in the close vicinity of IMT, and investigate the IMT driven by either strain or temperature independently. We found that the VO(2) insulating band gap narrows rapidly upon heating, and the infrared response undergoes an abrupt transition at both strain- and temperature-induced IMT. The results are consistent with recent studies attributing the opening of VO(2) insulating band gap to a correlation-assisted Peierls transition.

Separating low/high-valent ions with sub-nanometer sizes is a crucial yet challenging task in various areas (e.g., within environmental, healthcare, chemical, and energy engineering). Satisfying high separation precision requires membranes with exceptionally high selectivity. One way to realize this is constructing well-designed ion-selective nanochannels in pressure-driven membranes where the separation mechanism relies on combined steric, dielectric exclusion, and Donnan effects. To this aim, charged nanochannels in polyamide (PA) membranes are created by incorporating ionic polyamidoamine (PAMAM) dendrimers via interfacial polymerization. Both sub-10 nm sizes of the ionic PAMAM dendrimer molecules and their gradient distributions in the PA nanofilms contribute to the successful formation of defect-free PA nanofilms, containing both internal (intramolecular voids) and external (interfacial voids between the ionic PAMAM dendrimers and the PA matrix) nanochannels for fast transport of water molecules. The external nanochannels with tunable ionizable groups endow the PA membranes with both high low/high-valent co-ion selectivity and chemical cleaning tolerance, while the ion sieving/transport mechanism was analyzed by employing the Donnan steric pore model with dielectric exclusion.

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Electrolyte-gated organic field-effect transistors (EGOFETs) are emerging as a new frontier of organic bioelectronics, with promising applications in biosensing, pharmaceutical testing, and neuroscience. However, the limited charge carriers’ mobility and well-known environmental instability of conjugated polymers constrain the real applications of organic bioelectronics. Here, we comparatively studied the electrochemical stability of p-type conjugated polymer films in the EGOFET configuration. By combining electrochemical stability tests, morphology characterization, and EQCM-D monitoring, we find that a donor–acceptor copolymer, poly­(N-alkyldiketopyrrolo-pyrrole-dithienylthieno­[3,2-b]­thiophene) (DPP-DTT) shows improved mobility and electrochemical stability under an electrolyte, which may benefit from the ordered morphology and close alkyl side-chains’ interdigitation preventing water diffusion and ion doping during long-term operation under an electrolyte. Based on the DPP-DTT EGOFETs, we have demonstrated a low-cost drug toxicity test platform that is sensitive enough to distinguish the cytotoxicity of different chemicals. This study overall pushes forward the development of organic bioelectronics with enhanced stability and sensitivity and presents successful exploitation of EGOFET in pharmaceutical research.

The electronic structures and excitation properties of dye sensitizers determine the photon-to-current conversion efficiency of dye sensitized solar cells (DSSCs). In order to understand the different performance of porphyrin dye sensitizers YD2 and YD2-o-C8 in DSSC, their geometries and electronic structures have been studied using density functional theory (DFT), and the electronic absorption properties have been investigated via time-dependent DFT (TDDFT) with polarizable continuum model for solvent effects. The geometrical parameters indicate that YD2 and YD2-o-C8 have similar conjugate length and charge transfer (CT) distance. According to the experimental spectra, the HSE06 functional in TDDFT is the most suitable functional for describing the Q and B absorption bands of porphyrins. The transition configurations and molecular orbital analysis suggest that the diarylamino groups are major chromophores for effective CT excitations (ECTE), and therefore act as electron donor in photon-induced electron injection in DSSCs. The analysis of excited states properties and the free energy changes for electron injection support that the better performance of YD2-o-C8 in DSSCs result from the more excited states with ECTE character and the larger absolute value of free energy change for electron injection.

Interface engineering mediated by a designed chemical agent is of paramount importance for developing high-performance perovskite solar cells (PSCs). It is especially critical for planar SnO2-based PSCs due to the presence of abundant surface defects on SnO2 and/or perovskite surfaces. Herein, a novel multifunctional agent histidine (abbreviated as His) capable of cross-linking SnO2 and perovskite is employed to modify the SnO2/perovskite interface. Density functional theory (DFT) calculations and experimental results demonstrate that the carboxylate oxygen of His can form a Sn–O bond to fill the oxygen vacancies on the surface of SnO2, while its positively charged imidazole ring can occupy the cationic vacancies and its −NH3 + group interacts with the I– ion on the perovskite lattice. This cross-linking contributes to the significantly decreased interfacial trap state density and nonradiative recombination loss. In addition, it facilitates electron extraction/transfer and also improves interfacial contact and the quality of perovskite film. Correspondingly, the His-modified device delivers a superior power conversion efficiency (PCE) of 22.91% (improved from 20.13%) and an excellent open-circuit voltage (V oc) of 1.17 V (improved from 1.11 V), along with significantly suppressed hysteresis. Furthermore, the unencapsulated device based on His modification shows much better humidity and thermal stability than the pristine one. The present work provides guidance for the design of innovative multifunctional interfacial material for highly efficient PSCs.

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