Improving narrow bandgap a-SiGe:H alloys grown by hot-wire chemical vapor deposition

We have improved the electronic properties of narrow-bandgap (Tauc gap below 1.5 eV) amorphous-silicon germanium alloys (a-SiGe:H) grown by hot-wire chemical vapor deposition (HWCVD) by lowering the substrate temperature and deposition rate. Prior to this work, we were unable to grow a-SiGe:H alloys with bandgaps below 1.5 eV that had photo-to-dark conductivity ratios comparable with our plasma-enhanced CVD (PECVD) grown materials [B.P. Nelson et al., Mater. Res. Soc. Symp. 507 (1998) 447]. Decreasing the filament diameter from our standard configuration of 0.5 mm to 0.38 or 0.25 mm provides first big improvements in the photoresponse of these alloys. Lowering the substrate temperature from our previous optimal temperatures (T_sub starting at 435 °C) to at 250 °C provides additional photo-to-dark conductivity ratio increasing by two orders of magnitude for growth conditions containing 20–30% GeH₄ in the gas phase (relative to the total GeH₄+SiH₄ flow).     

人血清白蛋白对模拟宫腔液中铜的光电响应特性的影响

用动电位伏安法，动电位光电流测量，表面膜的阴极还原和XRD分析等手段研究了铜在含或不含人血清白蛋白的模拟宫腔液（pH=7)中的电化学和光电化学行为，在不含白蛋白的模拟宫腔液中，铜电极表面生成的Cu2O呈n型光响应；一定量白蛋白存在时使Cu2O的光响应从n型转为p型，Cu2O在模拟宫腔液中呈n型光响应可归因于氯离子对Cu2O的掺杂，白蛋白排斥氯离子对Cu2O的掺杂，使其光响应从n型转为p型。     

Visible light active Au:TiO2 nanocomposite photoanodes for water splitting: Sol–gel vs. sputtering

In this study, pure TiO₂ and Au:TiO₂ nanocomposite thin films are both synthesized using sol–gel and RF reactive co-sputtering methods. Physical and photoelectrochemical properties of the thin films deposited by each method are compared. The optical density spectra and scanning electron microscopy images of the Au:TiO₂ films reveal formation of gold nanoparticles in the all nanocomposite films synthesized by two methods. Moreover, the optical bandgap energy of the thin films decreases with addition of Au nanoparticles. X-ray photoelectron spectroscopy indicates that the presence of gold in metallic state and the formation of TiO₂ is stoichiometric. The photoelectrochemical properties of the TiO₂ and Au:TiO₂ thin films are characterized by using a compartment cell containing KOH solution as electrolyte. It is found that in the pure systems, TiO₂ sputtered films shows a higher photocurrent under visible light illumination while a reverse result is obtained for the Au:TiO₂ systems. In addition, photoirradiation on electrode/electrolyte (EE) and substrate/electrode (SE) interfaces for the sputtered samples reveals the EE illumination enhances the photoresponse of the layers as compared to SE case.     

Photosensitive nanostructured TiO2 grown at room temperature by novel “bottom-up” approached CBD method

The current paper incorporates with a “bottom-up” approached chemical bath deposition method to grow titanium dioxide (TiO₂) nanostructure at room temperature on glass and stainless steel substrates. The room temperature deposited TiO₂ films are heat treated at 673 K for 1 h in air and the corresponding change in structural, morphological and optical properties are studied by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and UV-VIS-NIR spectrophotometer. The heat-treated films are utilized as a photocathode in photoelectrochemical (PEC) cell in 1 M NaOH electrolyte. The experimental results show that, the CBD method allows formation of photosensitive, anatase TiO₂ thin film, which can be potentially tuned in many functional applications with feasibility.     

Fabrication of azobenzene-functionalized porous polymers for selective CO2 capture

Many solid adsorbents have been prepared for the CO₂ capture. In particular, the photoresponsive adsorbents have attracted extensive interests because of their tunable pore structure and variable responsive behaviors provoked by the external light. However, it is challenging to fabricate the photoresponsive adsorbents featured the big CO₂ capacity and high CO₂ selectivity. Herein, copolymerized between 4-phenylazobenzoyl chloride, 2,4,6-trichloro-1,3,5-triazine and melamine, a series of azobenzene-functionalized porous polymers (PTM-AZOs) are successfully synthesized. The PTM-AZOs are verified in possession of proper pore structures, large surface area and photoconductive properties through a series of characterization. The PTM-AZO-2 with the trans-isomerization exhibits the best CO₂ adsorption amount of 2.7 mmol·g^-1 (273 K and 0.1 MPa), while the CO₂/N₂ selectivity can reach 2459 and 607 on the trans- and cis-isomerization, respectively. The regulatable pore structures controlled by the photoresponsive azobenzene groups affect the CO₂ capture performance of the PTM-AZOs.     

Photoabsorption in carbon and silicon layer of phosphorous doped camphoric carbon/p-silicon (n-CC/p-Si) solar cell

Photoresponse characteristics of heterostructure solar cells, fabricated by depositing a phosphorous (P) doped carbon (n-C) layer on a p-type silicon (Si) substrate (n-C/p-Si cell), have been studied. The camphoric carbon (CC) targets containing varying amounts of P ranging from 1% to 7% by mass were used in a pulsed laser deposition chamber for the deposition of the carbon layers of the cells under analysis. The quantum efficiency of these cells was measured in the ultraviolet-visible-infrared region (300-1200 nm), which is found to vary with the P content in the carbon layer. The individual contributions of the carbon and silicon regions to the overall photoresponse are extracted by deconvoluting the overall photoresponse spectra. The relative contribution of the carbon region is found to increase with the P content up to 5 wt.% P in the carbon layer of the cell and decreases thereafter. This trend is similar to that of the optoelectronic properties of the P-doped CC films.     

Organic quantum wells with multiple negative differential resistance peaks and its photoswitch effect

Organic optoelectronic devices have experienced great progress in recent decades. However, quantum well has long been a challenge for organic semiconductors due to the weak intermolecular interactions, the difficulty of realizing high quality alternate crystalline films. Here, we construct a type II organic crystalline quantum well, in which both electron quantum well and hole quantum well show symmetrical and multiple negative differential resistance peaks, respectively. The blueshifts of absorption spectra and the peak voltage decreasing under illumination conditions are observed. Due to high absorption coefficient of organic semiconductors, photoswitch effect by taking advantage of negative differential resistance of organic quantum well, which owns very thin device structure is demonstrated. Our results prove the promising applications of organic quantum wells, which broaden the types of organic optoelectronic devices.     

Intercalation of cationic azobenzene derivatives in a synthetic mica and their photoresponse

Four types of cationic azobenzene derivatives (Azds) having quaternary ammonium functional group at the 4-position (“single-hand”) or at the 4 and 4′-positions (“double-hand”) were synthesized and intercalated in a synthetic mica, Li taeniolite (LiTN), by ion exchange to obtain photoresponsive complexes. Powder X-ray results suggested that the long axis of molecules was at an angle of 58–62° from the mica layer for the single-hand series and at about 24° for the double-hand series. Photoresponse by ultraviolet (UV) irradiation with λ=365 nm and visible light (VIS) with λ=436 nm was monitored by the change in d(001), the basal spacing. Each Azd/TN complex showed different types of behavior toward UV/VIS irradiation. Complexes of a double-hand azo derivative showed a basal-spacing contraction of 0.7% under UV irradiation, but recovered their initial length under VIS irradiation, or by standing in the dark. Another complex presented a nonreversible change in basal spacing of 4%. This contraction under UV irradiation was attributed to trans-to-cis isomerization of the azobenzene moiety in guests, although the complex interlayer-space environment may have caused a different response after contraction.     

Optoelectronic properties of In-doped SnS thin films

Nanostructured un- and In-doped SnS thin films were deposited on fluorine-doped tin oxide (FTO) substrates via an electrochemical deposition technique. The deposited thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectroscopy and UV–visible spectroscopy. The XRD patterns demonstrated that all deposited thin films are made of polycrystalline SnS particles. The AFM images illustrated a distinct change in the surface topography of the SnS thin films due to In-doping. The PL spectra showed two blue emission peaks and a green emission peak for all samples. Also, they highlighted a PL peak for the In-doped thin films. The incorporation of In-dopant leads to enhance in the optical absorption of SnS lattice. The optical energy band gap (E_g) of the deposited thin films was estimated using UV–vis spectroscopy, which indicated that In-doping decreases the E_g value of SnS thin films by creating defect levels. The photocurrent results demonstrated a higher photocurrent response and photocurrent amplitude for the In-doped SnS samples relative to the un-doped SnS thin film. The Mott–Schottky analysis revealed p-type conductivity for all samples. In addition, the carrier concentration of SnS was increased after In doping. The EIS spectra declared that In-doping improves the rate of charge transfer for SnS thin films. The charge transfer resistance of In-doped SnS decreased compared to the undoped SnS thin film. Finally, according to the J-V characteristics, the conversion efficiency of the In-doped SnS thin films was higher than that of the un-doped SnS sample. Therefore, the optical and electrical performance of SnS thin films were improved due to In-doping.     

Quantum Dot Infrared Photodetectors: Photoresponse Enhancement Due to Potential Barriers

Potential barriers around quantum dots (QDs) play a key role in kinetics of photoelectrons. These barriers are always created, when electrons from dopants outside QDs fill the dots. Potential barriers suppress the capture processes of photoelectrons and increase the photoresponse. To directly investigate the effect of potential barriers on photoelectron kinetics, we fabricated several QD structures with different positions of dopants and various levels of doping. The potential barriers as a function of doping and dopant positions have been determined using nextnano³ software. We experimentally investigated the photoresponse to IR radiation as a function of the radiation frequency and voltage bias. We also measured the dark current in these QD structures. Our investigations show that the photoresponse increases ~30 times as the height of potential barriers changes from 30 to 130 meV.