Synthesis mechanism of Pr doped BaTi_4O_9 powder by sol-gel process

Pr Doped BaTi4O9 gel was prepared by sol-gel method using Ti （OC4H9）4, Ba（CH3COO）2, CH3COOH and CH3OCH2CH2OH as raw materials. Through analyzing dry gel thermal treated at different temperatures, the possible synthesis mechanism of Pr doped BaTi4O9 powder was discussed. At first, Ti （ OC4 H9 ） 4 hydrolyzes and three dimensional networks form, in which Ba^2＋ and CH3COO^- are mostly in the form of ions; organic solvent is gradually volatilized through ealefaetion at 700 ℃, then the offspring is turned into BaTi5O11. With the temperature increasing to 850 ℃, BaTi5O11 begins resolving partly and forming BaTi4Og, and at 1000℃ Ba4Ti13O22 forms partly, but BaTi409 is the main crystal phase. BaTi5O11 and Ba4Ti13O30 decomposes completely at 1200℃ and forms single-phase BaTi4O9. The infrared （IR） analysis also shows that the absorbing peak of Ti-O bond is not in the characteristic absorption range of Ti- O -Ti （700 -900 cm^-1）, but slightly shifted to the higher end （908 cm^-1 ）. It is probably because that doping Pr enters into the crystal lattice and causes the abnormal absorption of Ti-O bond.

Control of organic–inorganic halide perovskites in solid-state solar cells: a perspective

Since the year of 2009 when the first appli- cation of organohalide lead perovskite as the light har- vester in solar cells was reported, tremendous attention has been devoted to these new types of perovskite-based solid-state solar cells and remarkable power conversion efficiency of over 20 % has been achieved to date. In this review, we first introduce the properties of organic- inorganic halide perovskites and then focus on the notable achievements made on the perovskite layer to improve the power conversion efficiency of solid-state perovskite solar cells, which is featured by process engineering of the state-of-the-art lead methylammoni- um triiodide perovskite and material control of lead triiodide perovskites and other newly emerged per- ovskites. In the end, we wish to provide an outlook of the future development in solid-state perovskite solar cells. Provided that the instability and toxicity of solid- state perovskite solar cells can be solved, we will wit- ness a new era for cost-effective and efficient solar cells.

Electrochemical impedance spectra of CdSe quantume dots sensitized nanocrystalline TiO_2 solar cells

Quantum dots sensitized nanocrystalline Tit2 solar cells （QDSSCs） are promising third-generation pbotovoltalc devices. In comparison with conventional dye-sensitized solar cells （DSSCs）, the efficiency of QDSSCs is still very low （about 3%）. In this paper, the electrochemical impedance spectroscopy technology has been adopted to investigate the quasi-Fermi level and the cartier dynamics of the colloidal CdSe QDs sensitized Tit2 eletrode with S2-/Sf redox electrolytes and the series resistance of the QDSSCs. In comparison with the conventional DSSCs with I^-3/Г as redox electrolytes, the energy difference between the conduction band edge and the quasi-Fermi levels of the Tit2 films （or the Fermi levels of the redox electrolytes） in QDSSCs has been decreased by about 0.3 V, resulting in the decrease of Voc by this value. The increases of the electrolyte dif- fussion resistance and the charge transfer resistance between Pt counter electrodes and S2-/Sx redox electrolytes were attributed to the decrease of the fill factors. However, the electron lifetime and electron diffussion length for QDSSCs are longer than those for DSSCs due to the retardation of the electron recombination by the adsorbed cysteine at the surfaces of the TiO2 films. It is indicated that electron recombination at the TiO2/electrolyte interface is not the main reason for the lower Jsc of the colloidal QDs sensitized QDSSCs. Improving light harvesting efficiency and photoelectron injection efficiency should be considered in the future for such kind of QDSSCs.

Method for improving illumination instability of organic-inorganic halide perovskite solar cells

Organohalogen perovskites are attracting con- siderable attention for use in solar cells. However, the stability of these devices will determine whether they can be made commercially viable. Device encapsulation or the use of a hydrophobic hole-transporting material can pre- vent the permeation of water into the perovskite layer and enhance the humidity stability of the cells under dark conditions. With regard to the light stability of solar cells, recent studies have yielded contradictory results. This work investigated the degradation mechanism of perovskite solar cells under illumination. Further, a simple method was proposed for improving their illumination stability. Amino acids were inserted between the compact TiO2 layer and the perovskite layer to effectively prevent the decomposition of the perovskite layer owing to the superoxide anions and hydroxyl radicals generated under illumination from the H2O and O2 adsorbed onto the TiO2 layer.