Feng-Yan Li

Nankai University, T’ien-ching-shih, Tianjin Shi, China

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Publications (8)12.51 Total impact

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    ABSTRACT: In the selenization process, the sputtered metallic precursors transformed into CIGS thin films, which were investigated by novel in-situ resistance measurement. Simultaneously, the crystal phases and thicknesses of the selenized thin films at various selenization temperatures are obtained by XRD and XRF, respectively. According to the analysis of phase evolutions and reaction characteristics, it can be confirmed metallic In existed in the precursors will transform into the In–Se compound directly and then results in CIS formation as well as the thickness increase below 370 °C. Otherwise, if alloy phases Cu–In and Cu–Ga co-exist in the precursors, not CIS but CIGS will form above 470°, which will lead to both thickness and resistance increase in the corresponding temperature range. Consequently, it can be concluded the thickness increase are decided by the formation of CIS or CIGS, whereas the strong reaction peak in the temperature-resistance curves are caused only by stoichiometric CIGS.
    Current Applied Physics - CURR APPL PHYS. 01/2011; 11(3):327-330.
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    ABSTRACT: In this work the selenization reactions and reaction paths in CuInxGa1-xSe2 thin films prepared by sputtering and post-selenization process are investigated. The in-situ electrical resistance measurement technique is applied to monitor all the selenization reactions. The crystal structure is determined by X-ray diffraction (XRD) measurement. From the analysis of resistance-temperature curves and the XRD patterns, the phase evolutions of various crystalline and selenization reaction paths have been obtained. From these measurements, the reaction mechanisms and kinetics in the CuInGa–Se system are further understood.
    Thin Solid Films 10/2010; 519(1):244-250. · 1.87 Impact Factor
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    ABSTRACT: As precursors are deposited in different sequences, the alloy phases of Cu–In or Cu–Ga are observed. This leads to different selenized results, which consist of either the single quaternary CIGS or the phase-separated CIS and CIGS mixture. According to the analysis of experimental results, it can be concluded that the alloy phases in the precursors have a significant impact on the reaction mechanism and path in the selenization process. It is the Cu–Ga alloy phase in the precursors that suppresses the rapid transformation of Cu–In to CuInSe2. Hence at 450 °C the Cu–Ga and Cu–In can react together with Se to form CIGS. With higher temperature annealing at 560 °C, the single quaternary CuIn0.7Ga0.3Se2 phase can be obtained.
    Journal of Physics D Applied Physics 06/2009; 42(12):125303. · 2.53 Impact Factor
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    ABSTRACT: During the selenization process of CIGS thin films, the relation between the element loss rate and the precursor depositions are analyzed. The growth of the CIGS thin films during the selenization process is investigated by the novel in situ resistance measurement, by which the formation of compound semiconductors can be observed directly and simultaneously. Their structures, phase evolutions and element losses are analyzed by XRD and XRF. Based on the experimental results, it can be concluded that the phase transforms have nothing to do with the deposition sequences of precursors, while the element loss rates are related to the deposition sequences in this process. In addition, element loss mechanisms of CIGS thin films prepared by the selenization process are analyzed by the phase evolutions and chemical combined path in the In, Ga–Se reaction processes. Moreover it is verified that the element losses are depressed by increasing the ramping-up rate finally. The results provide effective methods to fabricate high-quality CIGS thin films with low element losses.
    Semiconductor Science and Technology 02/2009; 24(3):035019. · 1.92 Impact Factor
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    ABSTRACT: One-step electrodeposition(ED) of Cu(In1-x, Gax)Se2 (CIGS) thin films on Mo/glass substrates from aqueous solutions containing CuCl2, InCl3, GaCl3, and H2SeO3 was studied. In order to stabilize the solutions, they were buffered using a potassium biphthalate/sulfamic acid mixture giving a bath of pH 2.5. The type of the solutions would influence Ga concentration in the CIGS films. In general, CIGS thin film is called stoichiometric compound when the molar ratio of Cu to In+Ga is 1, and when the ratio is in the range of 0.8-1, it is called near stoichiometric and slightly Cu-poor or In-rich CIGS compound. As-deposited films were near stoichiometric and slightly Cu-poor CIGS precursors with smooth, compact, crack-free surface by the optimization of the solution composition and the deposition condition. The electrodeposition mechanisms of CIGS on Mo substrates were studied by cyclic voltammetry. The results showed that Se4+ was first reduced to Se, and then Cu2+, In3 +, and Ga3+ were deposited via the induced co- deposition mechanism at more positive potentials than they were reduced. As-deposited films were selenized and recrystallized at 550 in Se vapor with a Se source temperature of 280 , which improved crystal structure of the films and changed little the compositions of ED-CIGS thin films, but resulted in cracking of the films.
    ACTA PHYSICO-CHIMICA SINICA 06/2008; 24(6). · 0.87 Impact Factor
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    ABSTRACT: Chalchopyrite CIGS thin films were prepared by the two-stage growth technique. The processes were based on the controlled selenization of sputtering metallic precursors with elemental Se vapor in closed space. The modified selenization process by fitting data prevented the substantial losses and the formation of voids from the interior of absorbers. Accordingly, adhesion was improved and the grain was enlarged, which could span throughout the entire film from the surface towards the Mo back electrode. In addition, a single-phased CIGS thin film was obtained by this selenization process simultaneously.
    Conference Record of the IEEE Photovoltaic Specialists Conference 01/2008;
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    ABSTRACT: In the present paper, the properties of Cu(In(1-x) Ga(x)) Se2 (CIGS) thin film absorber materials for the solar cells obtained by selenization of the precursors with In-rich or CuGa-rich surface layers were studied by XRD, SEM and Raman spectra. The photovoltaic devices based on the absorbers were measured and analyzed by illuminated J-V curve subsequently. The performance of the device constructed by the absorbers obtained by selenization of the precursors with CuGa-rich surface layer was improved greatly compared to that with In-rich surface layer. Through Raman spectra measurement, it was found that the Raman peak of the A1 mode was shifted for the CuGa-rich one, which is verified that the band gap of the surface layers was elevated. Moreover the value of increased Ga contents within the surface region of films were calculated by the relation between the Raman shifts and the Ga contents. As a result, the devices based on the thin films with the elevated surface energy band by selenizing the precursors with the CuGa-rich surface layer improved further the V(oc) and FF by about 74 mV and 8% respectively compared to that of corresponding to the one with In-rich surface layers, so that the conversion efficiency of the photovoltaic devices based on these thin films with CuGa-rich surface layer was improved by up to 9.4%. Meanwhile Raman scattering spectroscopy has proven to be a very powerful and useful technique for the surface analysis of such thin film solar cell semiconducuor materials.
    Guang pu xue yu guang pu fen xi = Guang pu 05/2007; 27(4):716-9. · 0.29 Impact Factor
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    ABSTRACT: In this paper, we study the structural, optical and electrical properties of polycrystalline Cu(In, Ga)Se2 (CIGS) thin films fabricated by the three-stage co-evaporation process on glass substrate at low substrate temperature (TSub). The structural, optical and electrical properties of the as-grown CIGS films have been investigated by X-ray diffraction spectra, transmittance and reflectance spectra, scanning electron microscope and temperature dependent Hall Effect measurement. The results reveal that the properties of the CIGS film deposited at low temperature strongly depend on the chemical composition. A CIGS solar cell with competitive conversion efficiency of 13.2% without anti-reflection layer using low-temperature process at TSub of 450 °C has been demonstrated. Our results suggest that the CIGS absorber for high efficiency solar cells via the low TSub process has a relatively narrow compositional ratio compared to the high TSub process.
    Solar Energy Materials and Solar Cells 99:356–361. · 5.03 Impact Factor