Raman scattering of polycrystalline GaSb thin films grown by the co-evaporation process

This paper reports that CaSb thin films have been co-deposited on soda-lime glass substrates. The GaSb thin film structural properties are characterized by Raman spectroscopy. The Sb-A1g/GaSb-TO ratio decreases rapidly with the increase of substrate temperature, which suggests a small amount of crystalline Sb in the GaSb thin film and suggests that Sb atoms in the thin film decrease. In Raman spectra, the transverse optical （TO） mode intensity is stronger than that of the longitudinal optical （LO） mode, which indicates that all the samples are disordered. The LO/TO intensity ratio increases with increasing substrate temperature which suggests the improved polycrystalline quality of the CaSb thin film. A downshift of the TO and LO frequencies of the polycrystalline CaSb thin film to single crystalline bulk GaSb Raman spectra is also observed. The uniaxial stress in GaSb thin film is calculated and the value is around 1.0 GPa. The uniaxial stress decreases with increasing substrate temperature. These results suggest that a higher substrate temperature is beneficial in relaxing the stress in GaSb thin film.

Influence of selenium evaporation temperature on the structure of Cu_2ZnSnSe_4 thin film deposited by a co-evaporation process

Cu2ZnSnSe4 （CZTSe） thin film solar cells have been fabricated using a one-step co-evaporation technique. The structural properties of polycrystalline CZTSe films deposited at different selenium evaporation temperatures （TSe） have been investigated using X-ray diffraction spectra, scanning electron microscopy, and atomic force microscopy. A relationship between TSe and the secondary phases deposited in the initial stage is established to explain the experimental observations. The Se flux is not necessarily increased too much to reduce Sn loss and the consumption of Se during fabrication could also be reduced. The best solar cell, with an efficiency of 2.32%, was obtained at a medium Tse of 230 ℃ （active area 0.34 cm2）.

Polycrystalline GaSb thin films grown by co-evaporation

We report optical and electrical properties of polycrystalline GaSb thin films which were successfully grown by co-evaporation on soda-lime glass substrates. The thin films have preferential orientation of the （111） direction. SEM results indicate that the average grain size of GaSb thin film is 500 nm with the substrate temperature of 560 ℃. The average reflectance of GaSb thin film is about 30% and the absorption coefficient is of the order of 10^4 cm^-1. The optical bandgap of GaSb thin film is 0.726 eV. The hole concentration shows a clear increasing trend as the Ga-evaporation-temperature/Sb-evaporation-temperature （TGa/Tsb） ratio increases. When the Ga crucible temperature is 810 ℃ and the antinomy crucible temperature is 415 ℃, the hole concentration of polycrystalline GaSb is 2 × 10^17 cm^-3 and the hole mobility is 130 cm^2/（V·s）. These results suggest that polycrystalline GaSb thin film is a good candidate for the use as a cheap material in TPV cells.

The optimization functions of ICP discharge in preparation of Cu–Zn–Sn precursors and CZTS films by co-evaporation

Cu-Zn-Sn （CZT） precursors were successfully prepared on glass substrate with the introduction of the assistant technology ICP （inductively coupled plasma） based on the conventional co-evaporation process. The deposition was performed with the substrate temperature at 220℃ and the chamber pressure at 6.5 x 10-2 Pa. Argon plasma was investigated with a Langmuir probe. The plasma density and the electron temperature increased with the increasing of the discharge power. The impact oflCP discharge power on the structural and morphological properties of the CZT film were investigated with energy dispersive X-ray spectrometers （EDS）, X-ray diffraction （XRD）, and scanning electron microscopy （SEM）. XRD and EDS were combined to investigate the structure of the film. The results show that Zn loss exists during the evaporation and the loss can be reduced by increasing the ICP discharge power. From the observation on the scanning electron microscope, the grain size becomes larger with argon plasma＇s assistance. The preparation of the Cu2ZnSnS4 （CZTS） film and the measured properties demonstrate that the ICP would optimize the growth of the film.

Various Metal Sandwich Layer Oriented Efficiency Enhancement Superiority on CuInGaSe2 Thin Film Solar Cells

The good quality CuInGaSe2 (CIGS) thin film solar cells were fabricated on molybdenum metal coated soda lime glass substrate. Three-stage co-evaporation method was utilized for the fabrication of high quality p-type CIGS thin film absorber layer. Further, n-type CdS layer, high resistive intrinsic ZnO layer and transparent conducting AlZnO layers were fabricated by CBD method and vacuum sputtering methods. We made three various top metal sandwich grid patterns, i.e. Al, Al/Cu and Cu/Al which were utilized to investigate the metal sandwich layer oriented efficiency enhancement superiority on CuInGaSe2 thin film solar cells. The investigated specific CIGS solar cell device efficiency with respect to various top metal grid sandwich patterns is presented and discussed.

Composition engineering of Sb_2S_3 film enabling high performance solar cells

Sb_2S_3 is a kind of stable light absorption materials with suitable band gap, promising for practical applications. Here we demonstrate that the engineering on the composition ratio enables significant improvement in the device performance. We found that the co-evaporation of sulfur or antimony with Sb_2S_3 is able to generate sulfur-or antimony-rich Sb_2S_3. This composition does not generate essential influence on the crystal structure, optical band and film formability, while the carrier concentration and transport dynamics are considerably changed. The device investigations show that sulfur-rich Sb_2S_3 film is favorable for efficient energy conversion, while antimony-rich Sb_2S_3 leads to greatly decreased device performance. With optimizations on the sulfur-rich Sb_2S_3 films, the final power conversion efficiency reaches5.8%, which is the highest efficiency in thermal evaporation derived Sb_2S_3 solar cells.

Impact of Cu-rich growth on the Cu2ZnSnSe4 surface morphology and related solar cells behavior

Inorderto study the influence ofCu-rich growth on the performance ofthe Cu2ZnSnSe4 （CZTSe）thin film solar cells, a multi-stage co-evaporation process is applied. The CZTSe films are grown at a lower substrate temperature to reduce the existence time of Cux Sey at the first period caused by the volatility of SnSex. This study examines the surface morphology and device performance in Cu-rich growth and close-to-stoichiometric growth. Although the grain size of Cu-rich growth film increases a little, the difference was not dramatic as the results of CIGS reported previously. A model based on the grain boundary migration theory is proposed to explain the experimental results. The mechanisms of Cu-rich growth between CZTSe and CIGS might be different.