Honglie Shen

Structural and optical properties of Cu2SnS3 and Cu3SnS4 thin films by successive ionic layer adsorption and reaction

Thin films of Cu2SnS3 and Cu3SnS4 were obtained by sulfurizing (Cu, Sn)S structured precursors prepared by successive ionic layer absorption and reaction method. The results of energy dispersive spectroscopy (EDS) indicate that some loss in Sn with increasing sulfurization temperature. For the sulfurization temperatures of 380, 400 and 500xa0°C, tetragonal (I-42m) Cu2SnS3, cubic (F-43m) Cu2SnS3 and tetragonal (I-42m) Cu3SnS4 were formed, respectively. The combination of X-ray diffraction (XRD) results and Raman spectroscopy reveals that there are small Cu2−xS phase existing in the CTS thin films (400 and 500xa0°C). Scanning electron microscopy was used to study the morphology of the layers. The ternary compounds present a high optical absorption coefficient (>104xa0cm−1). The band gap energy (Eg) of the CTS thin films is estimated by reflection spectroscopy. The ternary compounds present a high optical absorption coefficient (>104xa0cm−1). The estimated band gap energy (Eg) is 1.05xa0eV for tetragonal (I-42m) Cu2SnS3, 1.19xa0eV for cubic (F-43m) Cu2SnS3, and 1.22xa0eV for tetragonal (I-42m) Cu3SnS4.

Sulfurization time effects on the growth of Cu2ZnSnS4 thin films by solution method

Cu2ZnSnS4 (CZTS) films were obtained by sulfurizing (Cu, Sn) S/ZnS structured precursors prepared by a combination of the successive ionic layer absorption and reaction method and the chemical bath deposition method, respectively. The effect of sulfurization time on structure, composition and optical properties of these CZTS thin films was studied. The results of energy dispersive spectroscopy indicate that the annealed CZTS thin films are of Cu-poor and Zn-rich states. The X-ray diffraction studies reveal that Cu2−xS phase exists in the annealed CZTS thin film prepared by sulfurization for 20xa0min, while the Raman spectroscopy analysis shows that there is a small Cu2SnS3 phase existing in those by sulfurization for 20 and 40xa0min. The band gap (Eg) of the annealed CZTS thin films, which are determined by reflection spectroscopy, varies from 1.49 to 1.56xa0eV depending on sulfurization time. The best CZTS thin film is the one prepared by sulfurization for 80xa0min, exhibiting a single kesterite structure, dense morphology, ideal band gap (Egxa0=xa01.55xa0eV) and high optical absorption coefficient (>104 cm−1).

Synthesis of Cu2ZnSnS4 films from sequentially electrodeposited Cu–Sn–Zn precursors and their structural and optical properties

The Cu2ZnSnS4 (CZTS) films are successfully prepared using a process of sequentially electrodeposited Cu–Sn–Zn precursors by a novel electrolyte formula and optimized parameters on Mo substrate, succeeded by annealing in saturated sulfur atmosphere. The results show that the Cu/Sn/Zn precursor sequence is strict, and optimized electro-deposition parameters are as follows: −0.6xa0V, 5xa0min for Cu, −1.2xa0V, 2xa0min for Sn, and −1.35xa0V, 10xa0min for Zn. Layered precursors firstly alloy into Cu6Sn5 and CuZn binary phases under low annealing temperature. Then Cu6Sn5 and CuZn alloys decompose in sulfur atmosphere, and form CuS, SnS and ZnS binary phases. Cu2SnS3 ternary phase forms through reaction between CuS and SnS with increasing the temperature. Finally, the CZTS film is synthesized through reaction among binary and ternary sulfides. The photoluminescence peak from the CZTS films synthesized at 550xa0°C for 1xa0h is about at 1.49xa0eV.

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method

The influence of annealing atmosphere on the phase formation of Cu–Sn–S ternary compound by SILAR method was studied. Structural, optical and electrical properties of the compound were studied for the samples annealed at 420xa0°C for 1xa0h in different atmosphere. X-ray diffraction and Raman spectra showed that Cu2SnS3 cubic phase was obtained in an atmosphere of nitrogen and sulfur vapor mixture, while Cu4SnS4 orthorhombic phase was obtained in H2S atmosphere. An optical band-gap of 0.98xa0eV was obtained for Cu2SnS3 and 0.93xa0eV for Cu4SnS4 phase. The activation energies are about 0.1xa0eV for Cu2SnS3 phase and 0.06xa0eV for the Cu4SnS4 phase in high temperature region, but those are about 0.007 and 0.009xa0eV for them in low temperature region respectively.

Cu2ZnSnS4 films by paste coating and their optoelectronic properties

Cu2ZnSnS4 (CZTS) thin films were prepared by a paste coating method as the absorb layer of solar cells. This method is more eco-friendly using ethanol as solvent and more convenient than traditional sol–gel method. The effects of sulfurization temperature on properties of thin film were studied. The results of X-ray diffraction and Raman spectroscopy showed the formation of kesterite structure of CZTS films. The scanning electron microscopy images revealed that CZTS thin film obtained at 550xa0°C were compact and uniform. The optical band gap of the CZTS film was about 1.5xa0eV, and the CZTS film had an obvious optoelectronic response. Moreover, CZTS solar cell was prepared with a conversion efficiency of 0.47xa0%.

Quaternary co-electrodeposition of the Cu2ZnSnS4 films as potential solar cell absorbers

Cu2ZnSnS4 (CZTS) films are successfully prepared on Mo substrate by electrochemical epitaxial method. An electrolyte contains 0.124xa0M CuSO4·5H2O, 0.14xa0M ZnSO4, 0.13xa0M SnCl2·2H2O, 0.16xa0M Na2S2O3·5H2O, 2.25xa0M NaOH, 1.36xa0M C6H5Na3O7, 1.00xa0M C4H6O6. The equilibrium potential for quaternary co-electrodeposited solution is set at −1.1 ∼ −1.20xa0V. The results show that elements are deposited in the following sequence: Cu/S/Zn/S/Cu/S/Sn/S…. The ternary and quaternary compounds are formed with the increasing temperature during annealing. Finally the CZTS film can be well formed at 550xa0°C. The resistivity of CZTS is about 5.6xa0×xa0104xa0Ωxa0cm.

Positive or negative gain: Role of thermal capture cross sections in impurity photovoltaic effect

In this work, we carried out a numerical study on the role of thermal capture cross sections in impurity photovoltaic (IPV) effect for silicon solar cells doped with indium. The short-circuit current density, the open-circuit voltage and the conversion efficiency of the IPV cell were calculated in dependence of variable electron and hole thermal capture cross sections of indium in silicon. We found that the thermal capture cross section of electron is crucial to the device performance and that of hole has few influence on the cell property for this IPV cell since acceptor-type indium impurity level is near the valence band edge. If the electron thermal capture cross section is less than 10−20u2009cm2, a positive gain of conversion efficiency for the IPV cell would be presented. We concluded that those impurities with small electron (or hole) thermal capture cross sections may be suitable for use in the IPV cell with acceptor-type (or donor-type) impurity level near the valence (or conduction) band edge. These...

Influence of annealing temperature on the properties of polycrystalline silicon films formed by rapid thermal annealing of a-Si:H films

In this work, rapid thermal annealing (RTA) was employed to crystallize the amorphous silicon films deposited by hot-wire chemical vapor deposition. The influence of annealing temperature on structural and electrical properties was studied by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and temperature-dependent conductivity measurement. The results show that the amorphous silicon films can be successfully crystallized by RTA in a very short time. The crystallinity and electrical properties of the poly-Si films was greatly improved as the RTA temperature increasing. When the temperature higher than 900xa0°C, the poly-Si films obtained the crystalline fraction above 95xa0%, and the hydrogen atoms almost disappeared in the poly-Si films. At the temperature of 1,100xa0°C, polycrystalline silicon films with conductivity of 16.4xa0Sxa0cm−1 is obtained, which is seven orders in magnitude higher than that of the film annealed at 700xa0°C.

Improvement of the Crystallinity of Silicon Films Deposited by Hot-Wire Chemical Vapor Deposition with Negative Substrate Bias

We have investigated the effect of negative substrate bias on microcrystalline silicon films deposited on glass and stainless steel by hot-wire chemical vapor deposition (HWCVD) to gain insight into the effect of negative substrate bias on crystallization. Structural characterization of the silicon films was performed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. It was found that the crystallinity of the films is obviously improved by applying the substrate bias, especially for films on stainless steel. At hot-wire temperature of 1800°C and negative substrate bias of −800xa0V, grain size as large as 200xa0nm was obtained on stainless-steel substrate with crystalline fraction 9% higher than that of films deposited on glass and 15% higher than that of films deposited without substrate bias. It is deduced that the improvement of the crystallinity is mainly related to the accelerated electrons emitted from the hot wires. The differences in this improvement between different substrates are caused by the different electrical potential of the substrates. A solar cell fabricated by HWCVD with −800xa0V substrate bias is demonstrated, showing an obviously higher conversion efficiency than that without substrate bias.

Polycrystalline silicon films fabricated by rapid thermal annealing

Poly-crystalline silicon (poly-Si) films were fabricated by rapid thermal annealing (RTA) of amorphous silicon films which were deposited on quartz by hot wire chemical vapor deposition. An insertion of Cr layer can significantly suppress the peeling of Si films during the RTA process. The effect of RTA parameters on the structural properties of poly-Si films was investigated by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the crystallinity of the poly-Si films is increased with the increase of RTA temperature and duration. A sharp peak at about 520xa0cm−1 is observed in the Raman spectra of poly-Si films annealed at 900 and 1,100xa0°C for 15xa0s indicating the excellent crystallinity of the poly-Si films fabricated by RTA. Poly-Si films with high crystalline fraction of 97.3xa0% were obtained by RTA at 1,100xa0°C for 20xa0s.