Jeng-Shin Ma

Microwave-assisted chemical bath deposition process to fabricate CdS buffer layers used in Cu(In,Ga)Se2 solar cells

A microwave-assisted chemical bath deposition process was successfully developed for preparing CdS buffer layers in Cu(In,Ga)Se2 solar cells. Crystallized CdS films with densified microstructures were formed on Cu(In,Ga)Se2 absorber layers at 55 °C. The duration of the reaction was only 4 min. Increasing the reaction temperature facilitated homogeneous precipitation and suppressed heterogeneous precipitation, thereby decreasing the thickness of CdS films, and reduced Voc, Jsc, FF, and the conversion efficiency. When CdS buffer layers were prepared at 55 °C, a conversion efficiency of 10.2% was achieved, and the corresponding values of Voc, Jsc, and FF were measured to be 0.574 V, 32.5 mA cm−2, and 55.0%, respectively. Moreover, as the reaction temperature was increased, the shunt conductance, the diode factor, and the saturated current worsened, owing to insufficient coverage of CdS films. Increasing the reaction temperature decreased the photoluminescence intensity of Cu(In,Ga)Se2 films covered by the prepared CdS films. This work demonstrates that the microwave-assisted chemical bath deposition process for preparing CdS buffer layers significantly shortened the reaction duration, and yielded high-efficiency Cu(In,Ga)Se2 solar cells.

Reaction mechanism and kinetics analysis of the phase transformation of TiO2 from the anatase phase to the rutile phase

The kinetic mechanism of the phase transformation of TiO2 from the anatase phase to the rutile phase was investigated. TiO2 powders were prepared with different pH value of the starting solution via the thermal hydrolysis method in this study. The pH values of the starting solutions have significant effects on the phase transformation temperatures of the thermal hydrolysis reaction. As the reaction temperatures were raised, the conversion from the anatase phase to the rutile phase was increased. A core–shell morphology of the prepared TiO2 samples was suggested via the signals of the anatase phase and the rutile phase in UV–vis spectrum analysis. Through the isothermal heating process of the reaction kinetics, the controlling reaction in the phase transformation process from the anatase phase to the rutile phase was determined to be the three-dimensional phase boundary controlled process. The activation energy of the phase transformation was increased with an increase in the pH value of the starting solution.