A chemical approach to controlling the work function of few‐layer graphene is investigated. Graphene films are synthesized on Cu foil by chemical vapor deposition. Six metal chlorides, AuCl3, IrCl3, MoCl3, OsCl3, PdCl2, and RhCl3, are used as dopants. The sheet resistance of the doped graphene decreases from 1100 Ω/sq to ≈500–700 Ω/sq and its transmittance at 550 nm also decreases from 96.7% to 93% for 20 mM AuCl3 due to the formation of metal particles. The sheet resistance and transmittance are reduced with increasing metal chloride concentration. The G peak in the Raman spectra is shifted to a higher wavenumber after metal chloride doping, which indicates a charge transfer from graphene to metal ions. The intensity ratio of ICC/IC−C increases with doping, indicating an electron transfer from graphene sheets to metal ions. Ultraviolet photoemission spectroscopy data shows that the work function of graphene increases from 4.2 eV to 5.0, 4.9, 4.8, 4.68, 5.0, and 5.14 eV for the graphene with 20 mM AuCl3, IrCl3, MoCl3, OsCl3, PdCl2, and RhCl3, respectively. It is considered that spontaneous charge transfer occurs from the specific energy level of graphene to the metal ions, thus increasing the work function.

Nanoscale topography of artificial substrates can greatly influence the fate of stem cells including adhesion, proliferation, and differentiation. Thus the design and manipulation of nanoscale stem cell culture platforms or scaffolds are of great importance as a strategy in stem cell and tissue engineering applications. In this report, we propose that a graphene oxide (GO) film is an efficient platform for modulating structure and function of human adipose-derived stem cells (hASCs). Using a self-assembly method, we successfully coated GO on glass for fabricating GO films. The hASCs grown on the GO films showed increased adhesion, indicated by a large number of focal adhesions, and higher correlation between the orientations of actin filaments and vinculin bands compared to hASCs grown on the glass (uncoated GO substrate). It was also found that the GO films showed the stronger affinity for hASCs than the glass. In addition, the GO film proved to be a suitable environment for the time-dependent viability of hASCs. The enhanced differentiation of hASCs included osteogenesis, adipogenesis, and epithelial genesis, while chondrogenic differentiation of hASCs was decreased, compared to tissue culture polystyrene as a control substrate. The data obtained here collectively demonstrates that the GO film is an efficient substratum for the adhesion, proliferation, and differentiation of hASCs.

A chemical approach was applied to decrease the work function of few-layer graphene. Li 2 CO 3 , K 2 CO 3 , Rb 2 CO 3 , and Cs 2 CO 3 were used as n-doping materials. The sheet resistance of graphene doped with carbonate salt slightly increased from 1100 to 1700−2500 Ω/sq, and the transmittance of doped graphene with 0.1 M alkali metal at 550 nm decreased from 96.7 to 96.1−94% due to the formation of metal particles on the surface of graphene. A higher sheet resistance and lower transmittance were obtained at a higher concentration of alkali metal carbonate. The G peak in the Raman spectra was shifted to a lower wavenumber after alkali metal carbonate doping and the intensity ratio of the carbon double bond to the carbon single bond decreased with doping in the X-ray photoemission spectroscopy spectra, suggesting the charge transfer from metal ions to graphene sheets. Ultraviolet photoemission spectroscopy data showed that the work function of the graphene sheets decreased from 4.25 eV to 3.8, 3.7, 3.5, and 3.4 eV for graphene doped with Li 2 CO 3 , K 2 CO 3 , Rb 2 CO 3 , and Cs 2 CO 3 , respectively. This suggested that spontaneous chemical combination occurred between the carbon atoms and alkali metal, thereby decreasing the work function.

An inorganic lead halide perovskite film, CsPbI, used as an absorber in perovskite solar cells (PSCs) was optimized by controlling the annealing temperature and the layer thickness. The CsPbI layer was synthesized by one-step coating of CsI mixed with PbI and a HI additive in N,N-dimethylformamide. The annealing temperature of the CsPbI film was varied from 80 to 120 °C for different durations and the thickness was controlled by changing the spin-coating rpm. After annealing the CsPbI layer at 100 °C under dark conditions for 10 min, a black phase of CsPbI was formed and the band gap was 1.69 eV. Most of the yellow spots disappeared, the surface coverage was almost 100%, and the rms roughness was minimized to 3.03 nm after annealing at 100 °C. The power conversion efficiency (PCE) of the CsPbI based PSC annealed at 100 °C was 4.88%. This high PCE value is attributed to the low yellow phase ratio, high surface coverage, low rms roughness, lower charge transport resistance, and lower charge accumulation. The loss ratio of the PCE of the CHNHPbICl and CsPbI based PSCs after keeping in air was 47 and 26%, respectively, indicating that the stability of the CsPbI based PSC is better than that of the CHNHPbICl based PSC. From these results, it is evident that CsPbI is a potential candidate for solar cell applications.

Sensors based on 2D rGO/2D MoS2 van der Waals hybrid composites exhibited high sensitivity, extreme selectivity, fast response/recovery, and good reliability to humidity detection.