Shanghai Center for Photovoltaics

Shanghai, China

Shanghai Center for Photovoltaics

Shanghai, China
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Cui Y.,CAS Shanghai Institute of Technical Physics | Zuo S.,Shanghai Center for Photovoltaics | Jiang J.,Shanghai Center for Photovoltaics | Yuan S.,CAS Shanghai Institute of Technical Physics | And 2 more authors.
Solar Energy Materials and Solar Cells | Year: 2011

Cu 2ZnSnS 4 thin films have been successfully prepared by a novel synthesis process that involves a single step deposition of Cu 2ZnSnS 4 followed by a post-annealing treatment at 550 °C for 60 min in the atmosphere of N 2H 2S (5%). The microstructure, morphology, composition and optical property of the film have been investigated in detail. It is found that the Na 2S 2O 35H 2O concentration in the solution has a significant effect on the Cu 2ZnSnS 4 thin films. X-ray diffraction data indicates that the annealed Cu 2ZnSnS 4 thin films have a kesterite structure with preferred orientation along the (1 1 2) plane. Uniform and compact topographies are observed in some annealed films. From the energy dispersive X-ray spectroscopy analysis, it can be seen that Cu-poor and Zn-rich Cu 2ZnSnS 4 thin films have been obtained. The direct band gap energy of the film is about 1.5 eV. © 2011 Elsevier B.V.


Ge J.,East China Normal University | Ge J.,Shanghai Center for Photovoltaics | Ge J.,University of Toledo | Chu J.,East China Normal University | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2014

Implementing bifacial photovoltaic devices based on transparent conducting oxides (TCO) as the front and back contacts is highly appealing to improve the efficiency of kesterite solar cells. The p-type In substituted Cu2ZnSnS4 (CZTIS) thin-film solar cell absorber has been fabricated on ITO glass by sulfurizing coelectroplated Cu-Zn-Sn-S precursors in H2S (5 vol %) atmosphere at 520 °C for 30 min. Experimental proof, including X-ray diffraction, Raman spectroscopy, UV-vis-NIR transmission/reflection spectra, PL spectra, and electron microscopies, is presented for the interfacial reaction between the ITO back contact and CZTS absorber. This aggressive reaction due to thermal processing contributes to substitutional diffusion of In into CZTS, formation of secondary phases and electrically conductive degradation of ITO back contact. The structural, lattice vibrational, optical absorption, and defective properties of the CZTIS alloy absorber layer have been analyzed and discussed. The new dopant In is desirably capable of improving the open circuit voltage deficit of kesterite device. However, the nonohmic back contact in the bifacial device negatively limits the open circuit voltage and fill factor, evidencing by illumination-/temperature-dependent J-V and frequency-dependent capacitance-voltage (C-V-f) measurements. A 3.4% efficient solar cell is demonstrated under simultaneously bifacial illumination from both sides of TCO front and back contacts. © 2014 American Chemical Society.


Wu Y.,Tongji University | Xia Z.,Tongji University | Liang Z.,Tongji University | Zhou J.,Tongji University | And 3 more authors.
Optics Express | Year: 2014

Semiconducting nanowire arrays have emerged as a promising route toward achieving high efficiencies in solar cells. Here we propose a perpendicular elliptical silicon nanowire (PEE-SiNW) array for broadband light absorption in thin film silicon solar cells. Simulation results reveal that light absorption enhancement is originated from the split of the principal modes as well as the excitation of high order modes caused by the asymmetry of the elliptical nanowires and the enhanced mode coupling between adjacent elliptical nanowires attained by the appropriate arrangement of nanowires. An ultimate efficiency of 29.1% is achieved for the optimal PEE-SiNW array, which is 16.4% higher than that of the circular SiNW array with the same fill fraction. © 2014 Optical Society of America.


He J.,East China Normal University | Sun L.,East China Normal University | Zhang K.,East China Normal University | Wang W.,East China Normal University | And 5 more authors.
Applied Surface Science | Year: 2013

Quaternary Cu2ZnSnS4 (CZTS) thin films were deposited on heated glass substrates directly from a non-stoichiometric quaternary CZTS target by radio-frequency (RF) magnetron sputtering process, followed by post-sulfurization in atmosphere of Ar + H2S(5%). The results of X-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM) show that post-annealed process can improve the crystallinity of CZTS thin films. Both XRD and Raman spectra analysis indicate the internal compressive stress relaxes in post-annealed CZTS thin films. Further transmission spectra demonstrate that the band gaps of post-annealed CZTS thin films are smaller than those of as-deposited due to the relaxation of internal compressive stress and the increase of Cu content in the post-annealed CZTS films. © 2012 Elsevier B.V. All rights reserved.


Ge J.,East China Normal University | Wu Y.,Shanghai Center for Photovoltaics | Zhang C.,Shanghai Center for Photovoltaics | Zuo S.,Shanghai Center for Photovoltaics | And 5 more authors.
Applied Surface Science | Year: 2012

The Cu 2ZnSnS 4 (CZTS) are produced by sulfurization of precursors cosputtering from Cu 2Sn and ZnS targets at two distinct ramping rates (2 °C/min and 21°C/min). Through the comparative analyses of scanning electron microscopy (SEM), energy dispersive of X-ray (EDS), X-ray diffraction (XRD), transmittance and Raman spectrum, it has been revealed that heating rate has a great impact on the reaction mechanism and characters of CZTS. The rapid heating rate 21°C/min has resulted in the appearance of bubble-like morphology and the concurrency of amorphous phases with CZTS. CZTS absorbers sulfurized at 2°C/min have exhibited a better crystallographic quality revealed by Raman spectroscopy and XRD pattern. However, XRD and transmittance have proved n-type SnS and Cu 4Sn 7S 16 phases concurrent with the slowly ramped CZTS films. Difference in the two ramping rates has also resulted in the variance of band gap and Raman primary mode of the final films. The slow sulfurization (2°C/min) superior to the rapid one (21°C/min) is beneficial to the growth of the expected CZTS in this work. © 2012 Elsevier B.V. All rights reserved.


He J.,East China Normal University | Sun L.,East China Normal University | Ding N.,East China Normal University | Kong H.,East China Normal University | And 6 more authors.
Journal of Alloys and Compounds | Year: 2012

Cu 2ZnSn(S,Se) 4 (CZTSSe) thin films have been firstly deposited on heating quartz substrates by pulsed laser deposition (PLD) method using one-step process. The results of energy dispersive X-ray (EDX) spectroscopy show that there are some discrepancies of the elemental composition between targets and thin films. However, structural and optical properties of CZTSSe thin films show good tolerance to the composition deviation from stoichiometry. Both X-ray diffraction (XRD) and Raman spectra analysis indicate the internal compressive stress exists in CZTSSe thin films. Further transmission spectra demonstrate that the band gaps of CZTSSe thin films are higher than those of CZTSSe bulks. The internal compressive stress and the deficiency of Cu content in the films contribute to the enlargement of the band gaps of CZTSSe thin films. © 2012 Elsevier B.V. All rights reserved.


Tao J.,East China Normal University | Liu J.,East China Normal University | He J.,East China Normal University | Zhang K.,East China Normal University | And 5 more authors.
RSC Advances | Year: 2014

Cu2ZnSnS4 (CZTS) absorbers have been successfully deposited on tin-doped indium oxide coated glass (ITO/glass) substrates by sulfurization process of co-electrodeposited Cu-Zn-Sn-S precursor thin films at various annealing temperatures ranging from 500 to 580 °C for 30 min in an atmosphere of Ar-H2S (6.5%). The effects of sulfurization temperature on the structure, morphology, composition and optical properties of CZTS thin films have been investigated in details. XRD and Raman measurements reveal that the intensity of preferential orientation along the (112) direction becomes relatively more intense and sharp with increasing annealing temperature. The morphological and chemical composition studies indicate the formation of compact and homogenous CZTS thin films with Cu-poor and Zn-rich composition at a sulfurization temperature of 560 °C. And its band gap energy is around 1.50 eV. The AZO/i-ZnO/CdS/CZTS/ITO/glass thin-film solar cell is fabricated with the CZTS absorber layer grown at an optimized sulfurization temperature of 560 °C. It shows a power conversion efficiency of 1.98% for a 0.25 cm 2 area with Voc = 490 mV, Jsc = 9.69 mA cm -2 and FF = 40.03%. © The Royal Society of Chemistry 2014.


He J.,East China Normal University | Sun L.,East China Normal University | Chen Y.,East China Normal University | Jiang J.,Shanghai Center for Photovoltaics | And 3 more authors.
RSC Advances | Year: 2014

Cu2ZnSnS4 (CZTS) thin films have been attracting considerable attention as candidates for new photovoltaic materials. As a typical vacuum process, a sputtering stacked metallic layer followed by a conventional slow thermal process (STP) is usually used. This method is complex and time-consuming. Furthermore, the volatilization of Zn and Sn elements is significant during the STP process. To simplify the CZTS fabrication process and solve the element volatilization problem, in this work CZTS thin film was fabricated using a single quaternary target Radio-Frequency (RF) magnetron sputtering process followed by a rapid thermal process (RTP). The effects of sulfurization temperature on the properties of CZTS thin films have been studied. The compositional analysis shows that a combination of a single target sputtering process and the RTP technique can significantly reduce the volatilization of Zn and Sn elements compared to the conventional STP process. The results of X-ray diffraction (XRD) patterns and Raman scatting spectra show that the sulfurized CZTS thin films have a polycrystalline kesterite crystal structure. If the sulfurization process is performed at lower temperature, a large amount of disorder among the Cu and Zn cations exists in the CZTS thin film which is investigated by using Raman scattering spectra. At 550 °C, the CZTS thin film has high quality of crystallinity with large grain size and dense morphology, its band gap energy is found to be 1.53 eV. The solar cell fabricated with the CZTS absorber grown at an optimized sulfurization temperature of 550 °C shows a conversion efficiency of 2.85% for a 0.16 cm2 area with Voc = 412 mV, Jsc = 17.9 mA cm-2, and FF = 40.5%. These results show that this process is suitable for the growth of kesterite CZTS solar cell absorbers. © 2014 the Partner Organisations.


Ge J.,East China Normal University | Ge J.,Shanghai Center for Photovoltaics | Jiang J.,Shanghai Center for Photovoltaics | Yang P.,East China Normal University | And 7 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

Thin film solar cells with a structure of ZnO/CdS/Cu2ZnSnS 4 (CZTS)/Mo were fabricated successfully by sulfurization of co-electrodeposited Cu-Zn-Sn-S precursors at 590°C for 15 min. The best solar cell performance was achieved with an efficiency of 5.5% (V OC=673.8 mV, JSC=18.7 mA cm-2, FF=44%). The vibrational properties and phase identification of the absorber were studied by the polarised Raman and IR spectra. The CZTS absorber layer shows a bi-layered structure comprising of a well-crystallized photovoltaic layer with metallic ratios of Cu/Zn=1.95 and Zn/Sn=1.56 and a particulate-like bottom layer with a heavily Sn poor content. These particulates in the bottom CZTS layer feature with a high density of stacking faults along with ZnS phases and contribute to the low minority lifetime, the high recombination losses, and the increased series resistances in the device. In the well-crystallized CZTS absorber layer the trace of a twin defect on {1 1 2} plane is discovered. Dark electrical analysis indicates there is a relatively small energy barrier height of 44 meV across the cell. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.


He J.,East China Normal University | Sun L.,East China Normal University | Chen Y.,East China Normal University | Jiang J.,Shanghai Center for Photovoltaics | And 3 more authors.
Journal of Power Sources | Year: 2015

Effects of sulfurization pressure on composition, morphology and microstructure of kesterite Cu2ZnSnS4 (CZTS) thin films obtained by sulfurization of the metallic layers have been investigated in detail. It is found that the S content in the CZTS thin films is strongly dependent on the sulfurization pressure. The CZTS thin films sulfurized under low sulfurization pressure have S-poor state with a bilayer structure, while it exhibits sufficient amounts of sulfur under high sulfurization pressure with grain growth throughout the entire absorber film. X-ray diffraction data indicate lower sulfurization pressure during the CZTS grain growth process can induce the formation of more structural defects in the CZTS lattice and the CZTS thin films sulfurized under high sulfurization pressure have more random orientation. Furthermore, ZnS and MoS2 phase exist in all samples determined by Fourier transform infrared reflectance spectroscopy as complementary to Raman spectroscopy. The solar cell fabricated with the CZTS thin film under 10 Torr sulfurization pressure shows the best conversion efficiency of 3.52% (VOC = 484 mV, JSC = 14.56 mA cm-2, FF = 50.1%). © 2014 Elsevier B.V.

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