Yang Renqiang

Photoluminescence and defect evolution of nano-ZnO thin films at low temperature annealing

Nano-ZnO thin films composed of nanoparticles with sizes of 10–16 nm on silicon substrates at low temperature were prepared by sol-gel method. By placing the nano-ZnO thin films at room temperature or annealing at 100°C in air for 10 h intermittently, within a total 70 h annealing time, the evolution of PL spectra of the nano-ZnO thin films were studied in detail. As the annealing time increases, the PL peaks shift from violet to blue and green bands. The PL peaks at violet and blue bands decrease with the annealing time, but the PL peaks at green band are opposite. The PL spectra are related to the defects in the nano-ZnO thin films. The PL peaks positioned at 430 nm are mainly related to defects of zinc interstatials (Zni), oxygen vacancies and (Vo); the ones at 420 nm to oxygen interstitials (Oi), Zinc vacancies (Vzn), Zni; and the ones at 468 nm to Vzn, Zni, and charged oxygen interstatials(Vo+). The green luminescence is related to Oi, Vo and Zni. The evolutions of PL spectra and the defects are also related to the concentrations of Zn in the thin films, the thicknesses of the films and the annealing time. For the films with 0.5 M and 1.0 M Zn concentrations, after 20 h and 30 h annealing in air at 100°C, respectively, either placing them in air at room temperature or continuing anneal in air at 100°C, the PL spectra are stable. Under the low temperature annealing, Zni decreases with the annealing time, and Oi increases. Sufficient Oi favors to keep the nano-ZnO thin films stable. This result is important to nano-ZnO thin films as electron transport layers in inverted or tandem organic solar cells.

Stepwise synthesis of cuprous oxide nanoparticles with adjustable structures and growth model

By stepwise adding of reducer N2H4·H2O, cuprous oxide (Cu2O) nanoparticles (NPs) with adjustable structures were synthesized. The features of Cu2O NPs were characterized by XRD, TEM and UV-Vis absorption spectra. When the reducer was added into the reactant system at one time, the sizes of the Cu2O NPs are in the range of 120–140 nm. Most Cu2O NPs are solid spheres. As the reducer was divided into two equal parts and stepwisely added, almost all the NPs are hollow spheres with good size (150–170 nm) distribution and dispersity. But when the reducer was divided into three or four equal parts and stepwisely added, the NPs are hollow spheres, core-shell structures or solid spheres, and the sizes distribution of the products is deteriorated. The effect of sodium hydrate (NaOH) was also probed. Addition of NaOH speeded up the nucleation and growth processes of Cu2O NPs. With the alkalinity increase, the shells of the hollow spheres become compact and the thicknesses of the shells increase, but the size distribution of the NPs is deteriorated. The absorption spectra of the Cu2O NPs are tunable. With the shell thicknesses increase, the absorption peaks have red shifts. An inside-outside growth model of Cu2O NPs was proposed to explain the results. The Cu2O single crystalline grains grow not only in the reactant solution, but also inside of the hollow nanospheres. The new Cu2O nanocrystallines can not only aggregate onto the shells of the nano hollow spheres, but also inside and outside of the hollow spheres, which leads to increasing the shell thicknesses of the hollow spheres, forming core-shell structures or small solid spheres of Cu2O NPs, respectively.

Efficient Annealing-Free P3HT:PC61BM-Based Organic Solar Cells by Using a Novel Solvent Additive without a Halogen or Sulphur Atom

The power conversion efficiency (PCE) of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) based organic solar cells (OSCs) is significantly improved by using benzyl acetate (BA), an organic compound without any halogen or sulphur atom, as a processing additive to control the blend morphology. The solar cells show PCE of 3.85% with a fill factor (FF) of 65.22%, which are higher than those of the common thermal annealing device (PCE 3.30%, FF 60.83%). The overall increased PCE depends upon the enhanced crystallinity of P3HT and good carriers transport, with a high balanced charge carrier mobility.