BHJ solar cells are typically fabricated with a transparent conductive anode (e.g. indium tin oxide, ITO), a low-work-function metal cathode (e.g., Al, Ca), and an active layer (a mixture of conjugated polymer and fullerene derivative) sandwiched between the anode and cathode. The BHJ layer and cathode dramatically affect the stability. In particular, the cathode is susceptible to degradation by oxygen and water vapor. Poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is often used as an anode buffer layer. Long-term stability is a problem because PEDOT:PSS is hygroscopic and acidic. [ 17–21 ]

Inverted Polymer Solar Cells Integrated with a Low‐Temperature‐Annealed Sol‐Gel‐Derived ZnO Film as an Electron Transport Layer

This study examined the origin of visible luminescence from ZnO layers deposited on p-Si substrates by various growth methods using temperature dependent photoluminescence measurements. The deep level emissions of ZnO layers are found to be strongly dependent on the growth conditions and growth methods used. For the samples grown by sputtering, the visible emission consisted of violet, green, and orange-red regions, which corresponded to zinc interstitial (Zni), oxygen vacancy (VO), and oxygen interstitial (Oi) defect levels, respectively. In contrast, the deep level emissions of metal organic chemical vapor deposition grown samples consisted of blue and green emissions and blue and orange-red emissions at low and high oxygen flow rates, respectively. The ZnO nanorods synthesized by thermal evaporation showed a dominant deep level emission at the green region, which is associated with oxygen vacancies (VO).

A comparative analysis of deep level emission in ZnO layers deposited by various methods

Unique porous ZnO polygonal nanoflakes were synthesized by the microwave hydrothermal method. The structural properties of the products were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and high-resolution TEM techniques. In situ diffuse reflectance infrared Fourier transform spectroscopy technique was employed to investigate the mechanism of NO2 sensing. Free nitrate ions, nitrate ions, and nitrite anions were the main adsorbed species. N2O was formed via NO– and N2O2– that were stemmed from NO. Comparative tests for gas sensing between gas sensors based on the as-prepared porous ZnO nanoflakes and purchased ZnO nanoparticles clearly showed that the former exhibited more excellent NO2 sensing performances. Photoluminescence and X-ray photoelectron spectroscopy spectra further proved that the intensities of donors (oxygen vacancy (VO) and/or zinc interstitial (Zni)) and surface oxygen species (O2– and O2), which were involved in the mechani...

Porous ZnO Polygonal Nanoflakes: Synthesis, Use in High-Sensitivity NO2 Gas Sensor, and Proposed Mechanism of Gas Sensing

Under visible light irradiation, excited electrons in heterojunction structure of Bi/BiOCl were transferred into oxygen vacancies states, and then to the Bi metal nanoparticles, resulting in effective separation of electron–hole pairs. The heterojunction photocatalyst exhibited an extraordinary high activity in photodegradation of RhB dye and persistent organic pollutants, i.e. RhB was completely degraded in 2 minutes.

A Bi/BiOCl heterojunction photocatalyst with enhanced electron–hole separation and excellent visible light photodegrading activity

The influence of defects on the photoactivity of ZnO has been revealed. The defects can be formed via ball-milling treatment, and part of the defects can be repaired via annealing treatment. The photocatalytic activity of the ZnO sharply decreased as the ball-milling speed and milling time increased. After the annealing treatment, the photocatalytic activity recovered partly but could not return to the activity of the pristine ZnO. The bulk defects such as oxygen vacancies (VO), zinc vacancies (VZn) and a lot of nonradiative defects were formed after the milling treatment. The annealing treatment can only repair part of the bulk defects and nonradiative defects. Thus, only part of the photoactivity was recovered. The species trapping experiments showed that the introduction of the bulk defects did not change the photocatalytic mechanism. The main oxidative species for the pristine ZnO, the milled ZnO, and the annealed ZnO are photogenerated holes and hydroxyl radicals.

Influence of Defects on the Photocatalytic Activity of ZnO

Zinc oxide (ZnO) thin films prepared on sapphire substrates by employing a pulsed laser deposition (PLD) have been annealed in vacuum, N 2 , and O 2 ambient at annealing temperature 600  ° C. X-ray diffraction (XRD) and atomic force microscopy (AFM) observation show that the annealed thin films possess (0 0 0 2) textured feature and form better crystal grains with a large size. X-ray photoelectron spectroscopy (XPS) and Raman analysis show the defects of ZnO thin films annealed in different ambient is distinctly different. The film annealed in vacuum possesses large oxygen vacancies (V o ) and Zn interstitials (Zn i ); while large surface defects exist in film annealed in N 2 ambient. The concentrations of the intrinsic and extrinsic defects are the lowest in ZnO thin film annealed in oxygen gas. Photoluminescence (PL) spectra also reveal that the ultraviolet (UV) emission is the best for thin film annealed in O 2 . The blue emission (2.66 eV) is ascribed to the electronic transition from the donor energy level of Zn interstitials to acceptor energy level of Zn vacancies rather than the O vacancy.

Blue luminescent centers and microstructural evaluation by XPS and Raman in ZnO thin films annealed in vacuum, N2 and O2

Zinc oxide (ZnO) thin films on Si (1 1 1) substrates were deposited by pulsed laser ablation of ZnO target at different oxygen pressures. A pulsed Nd:YAG laser with wavelength of 1064 nm was used as laser source. The deposited thin films have been characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and Raman spectroscopy. XRD measurements indicate that the ZnO thin films deposited at the oxygen pressure of 1.3 Pa have the best crystalline quality. AFM results show that the surface roughness of ZnO film increases with the increase of oxygen pressure. The Raman results indicate that oxygen ambient plays an important role in removing defects due to excess zinc.

Effects of oxygen pressures on pulsed laser deposition of ZnO films

GaN thin films were deposited on sapphire (0001) substrates at different nitrogen pressures by pulsed laser deposition (PLD) of GaN target in nitrogen atmosphere. Good single crystal GaN thin films were obtained after annealing at 1000 °C for 15 min in a NH3 atmosphere. An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as the laser source. The influence of nitrogen pressure on the thickness, crystallinity and surface morphology of GaN films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy. The results show that at low nitrogen pressure, the surface diffusion of adatoms can be influenced by the collisions between the nitrogen gas molecules and the activated atoms, which can influence the kinetic energy of the activated atoms. However, at high nitrogen pressure, the kinetic energy of adatoms is decided by the annealing temperature. In our experimental conditions, the GaN thin films deposited at 0.75 and 7.5 Pa have a high surface morphology and crystalline quality.

The effect of nitrogen pressure on the two-step method deposition of GaN films

GaN nanorods have been successfully synthesized on Si(111) substrates by magnetron sputtering through ammoniating Ga2O3/ZnO films at 950 °C in a quartz tube. The GaN nanorods are characterized by X-ray diffraction, scanning electron microscopy, field-emission transmission electron microscopy, X-ray photoelectron spectroscopy and fluorescence spectrophotometry. The results show that the nanorods have a pure hexagonal GaN wurtzite structure with lengths of about several micrometers and diameters of about 200 nm, and the growth direction of the GaN nanorods is parallel to the (101) plane. The photoluminescence spectrum indicates that the nanorods have a good emission property. Finally, the growth mechanism is also briefly discussed.

Growth and characterization of GaN nanorods through ammoniating process by magnetron sputtering on Si(111) substrates

The gallium nitride (GaN) films have been successfully fabricated on silicon (111) substrates through ammoniating Ga2O3 films deposited by electrophoresis. The structure and composition of the formed films were characterized by Fourier transform infrared (FTIR) transmission spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicate that the films formed in this study are polycrystalline GaN with hexagonal wurtzite structure.

H.Z. Zhuang

Papers

Blue luminescent centers and microstructural evaluation by XPS and Raman in ZnO thin films annealed in vacuum, N2 and O2

Effects of oxygen pressures on pulsed laser deposition of ZnO films

The effect of nitrogen pressure on the two-step method deposition of GaN films

Growth and characterization of GaN nanorods through ammoniating process by magnetron sputtering on Si(111) substrates

FORMATION OF GaN FILM BY AMMONIATING Ga2O3 DEPOSITED ON Si SUBSTRATE WITH ELECTROPHORESIS