Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe2 NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films. First Cu+ is substituted for Cd2+ transforming CdSe NCs to Cu-rich Cu2Se NC films. Next, Cu2Se NC films are dipped into a Na2Se solution to Se-enrich the NCs, thus compensating the Cu-rich surface, promoting fusion of the Cu2Se NCs, and providing sites for subsequent In-dopants. The liquid-coordination-complex trioctylphosphine–indium chloride (TOP–InCl3) is used as a source of In3+ to partially exchange and n-dope CuInSe2 NC films. We demonstrate Al2O3-encapsulated, air-stable CuInSe2 NC FETs with linear (saturation) electron mobilities of 8.2 ± 1.8 cm2/(V s) (10.5 ± 2.4 cm2/(V s)) and with current modulation of 105, comparable to that for high-performance Cd-, Pb-, and As-based NC FETs. The CuInSe2 NC FETs are used as building blocks of integrated inverters to demonstrate their promise for low-cost, low-toxicity NC circuits.

BiVO4 is a promising n-type semiconductor for photoelectrochemical (PEC) water splitting, which can serve as a photoanode. However, severe surface recombination and slow water oxidation kinetics hinder the realization of its highly theoretical PEC performance. Single-atom catalyst-like metal–organic frameworks (MOFs) and their derived metal oxides have been broadly investigated to enhance the kinetics of BiVO4 photoanodes. According to the principle of catalysis, only coordinatively unsaturated atoms can participate in the catalytic reaction. Herein, a defective cobalt-based MOF (d-CoMOF) with missing linker defects is modified onto the surface of N-doped BiVO4 (N:BVO) photoanodes. The photocurrent density of d-CoMOF/N:BVO is 3.59 times higher than that of pristine BVO (0.56 mA/cm2) at 1.23 VRHE. The onset potential of d-CoMOF/N:BVO shows a cathodic shift of 300 mV relative to BVO. The roles of the d-CoMOF overlayer and N doping are experimentally revealed. The d-CoMOF modification and N doping could increase the electron density, passivate the surface states, and promote the catalysis kinetics of BVO. Thus, the kinetic parameters, such as the charge separation/injection efficiency, onset potential, and photocurrent density, are significantly enhanced. This work provides a way to use MOFs for PEC water splitting by the introduction of defects.

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The poor conductivity and sluggish kinetics of hematite (α-Fe2O3) limit its photoelectrochemical (PEC) performance. Herein, a cobalt metal–organic framework (Co-MOF) ultrathin overlayer is in situ-grown onto a Ti-doped hematite nanorod array via the chemical bath deposition. The optimal Co-MOF/Ti:Fe2O3 achieves a photocurrent density of 2.24 mA/cm2 at 1.23 V [vs reversible hydrogen electrode (RHE)], which is 2.4-folds that of pristine Fe2O3. When compared with the onset potential of Ti:Fe2O3, Co-MOF/Ti:Fe2O3 exhibits a cathodic shift of 310 mV. Co-MOF/Ti:Fe2O3 also shows a photocurrent density retention of 98.1% after the 6 h stability test. The improved PEC activity is mostly ascribed to the increased charge separation and surface charge injection. Ti doping increases the electron density in Fe2O3 and lowers the Fermi level (vs RHE), facilitating the charge transport in the bulk. The enhanced photovoltage and favorable distribution of surface states after Co-MOF modification and the catalytic/conductive properties of Co-MOF induce the enhanced charge separation/injection and the low onset potential.

POMs) and carbon nanomaterials become a new option for achieving higher capacitance. [4] POMs are anionic metal-oxo clusters of [M x O y ] n− consisting of two or more metals (M, e.g., Mo, W, V) with high oxidation states which are linked by oxoligands. [5] Therefore POMs are the good candidates for supercapacitor due to their fast and reversible multi-electron redox reactions along with the high theoretical values. [6-8] However, POMs exhibit strong solubility in water and many organic solvents due to their anionic nature, which limits their broad application on supercapacitors. [9] Thus, tremendous efforts have been devoted to immobilizing POMs onto carbon materials. Anchoring POMs with carbon is extremely critical since it can not only prevent the dissolution of POMs but also enhance the conductivity. [10-14] There are three most straightforward and effective methods for the synthesis of POMcarbon composites: i) chemisorption, ii) self-assembly, and iii) immobilization in a polymer matrix. [8,15] For chemisorption, POMs molecules are usually adsorbed at defect sites (e.g., the surface functional groups, the crystal defects) by strong and irreversible bonding. Therefore the amount of chemisorbed POMs is dependent on the functionalization degree on carbon materials. [7] For self-assembly, since the POMs are electronegative in solution, the cationic polymer molecular should be used to modify the surface of carbon, such as polyethyleneimine (PEI), and poly(diallyldimethylammonium chloride) (PDDA). [16,17] For immobilization in a polymer matrix, it can be divided into two methods, including the two-step method and the one-step method. The former is POMs diffuse and incorporate into the previously deposited polymer matrix. The latter is the polymer film is formed in the presence of a POM solution. POMs with oxidative property can chemically polymerize monomer molecules to form a polymer film. [18] Meanwhile, the conductive polymer with intrinsic redox activity can contribute more pseudocapacitance. This inspires us to fabricate coaxial cable-like active fibers by using carbon nanotubes (CNTs) as conductive substrates, POMs as main active materials, and conductive polymer as a shield and active material. It is expected that the stability and specific capacitance could be significantly improved simultaneously. The pioneering study of Cs-PMo/chitosan/CNTs hybrid materials showed enhanced capacitance and good stability during 500 cycles. [19] Lian and co-workers demonstrated that the CNTs coated with the Polyoxometalate (POM) as one pseudocapacitive material could efficiently boost the capacitance of carbon materials. However, POM hydrolysis is a key obstacle in utilizing POM for supercapacitors, causing reduced cycling stability. Here, coaxial cable-like carbon nanotubes(CNTs)-based active fibers are synthesized for highly capacitive and stable supercapacitors. The POM layer of PMo 12 O 40 3− (PMo) is physically protected from the hydrolysis by the external polyaniline (PANI) layer. The optimal CNT/PMo/PANI fibers show...