Jae-Hyung Wi

Photovoltaic Performance and Interface Behaviors of Cu(In,Ga)Se2 Solar Cells with a Sputtered-Zn(O,S) Buffer Layer by High-Temperature Annealing

We selected a sputtered-Zn(O,S) film as a buffer material and fabricated a Cu(In,Ga)Se2 (CIGS) solar cell for use in monolithic tandem solar cells. A thermally stable buffer layer was required because it should withstand heat treatment during processing of top cell. Postannealing treatment was performed on a CIGS solar cell in vacuum at temperatures from 300-500 °C to examine its thermal stability. Serious device degradation particularly in VOC was observed, which was due to the diffusion of thermally activated constituent elements. The elements In and Ga tend to out-diffuse to the top surface of the CIGS, while Zn diffuses into the interface of Zn(O,S)/CIGS. Such rearrangement of atomic fractions modifies the local energy band gap and band alignment at the interface. The notch-shape induced at the interface after postannealing could function as an electrical trap during electron transport, which would result in the reduction of solar cell efficiency.

Light-soaking effects and capacitance profiling in Cu(In,Ga)Se2 thin-film solar cells with chemical-bath-deposited ZnS buffer layers

We fabricated Cu(In,Ga)Se2 (CIGS) solar cells with chemical-bath deposited (CBD) ZnS buffer layers with different deposition times. The conversion efficiency and the fill factor of the CIGS solar cells reveal a strong dependence on the deposition time of CBD-ZnS films. In order to understand the detailed relationship between the heterojunction structure and the electronic properties of CIGS solar cells with different deposition times of CBD-ZnS films, capacitance-voltage (C-V) profiling measurements with additional laser illumination were performed. The light-soaking effects on CIGS solar cells with a CBD-ZnS buffer layer were investigated in detail using current density-voltage (J-V) and C-V measurements with several different lasers with different emission wavelengths. After light-soaking, the conversion efficiency changed significantly and the double diode feature in J-V curves disappeared. We explain that the major reason for the improvement of efficiency by light-soaking is due to the fact that negatively charged and highly defective vacancies in the CIGS absorber near the interface of CBD-ZnS/CIGS were formed and became neutral due to carriers generated by ultra-violet absorption in the buffer layer.

ZnS buffer layer prepared by sulfurization of sputtered Zn film for Cu(In, Ga)Se 2 solar cells

We report on a novel method of a fabrication of a ZnS buffer layer for an application of Cu(In, Ga)Se2 (CIGS) solar cells. The ZnS thin film was prepared by a sulfurization of a sputtered Zn film using a sulfur cracker. The structural and optical properties of the ZnS films and the photovoltaic performance of the ZnS-employed CIGS solar cells were investigated. The thin ZnS film played a sufficient role as a buffer layer achieving the power conversion efficiency of 10.5%.

Temperature effect on Dry Etching of ZrO 2 in Cl 2 /BCl 3 /Ar Plasma

The wafer surface temperature is an important parameter in the etching process which influences the reaction probabilities of incident species, the vapor pressure of etch products, and the re-deposition of reaction products on feature surfaces. In this study, we investigated all of the effects of substrate temperature on the etch rate of thin film and selectivity of thin film over thin film in inductively coupled plasma as functions of addition in /Ar plasma, RF power and dc-bias voltage based on the substrate temperature in range of to . The elements on the surface were analyzed by x-ray photoelectron spectroscopy (XPS).