Synthesis and characterization of CuInSe2 thin films for photovoltaic cells by a solution-based depo.pdf
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1、Synthesis and characterization of CuInSe2 thin fi lms for photovoltaic cells by a solution-based deposition method Chae Rin Kim a, Seung Yeol Hanb, Chih Hung Changb, Tae Jin Leea, Si Ok Ryua,* aSchool of Display and Chemical Engineering, Yeungnam University, 214-1 Dae-dong, Gyeonsan, Gyeongbuk 712-7
2、49, Republic of Korea bSchool of Chemical Biological fax: +82 53 810 4631. E-mail address: soryuynu.ac.kr (S.O. Ryu). Current Applied Physics 10 (2010) S383S386 Contents lists available at ScienceDirect Current Applied Physics journal homepage: streams are allowed to mix together in the element. The
3、 resulting mixture from the element is passed through a temperature-con- trolled channel, which was maintained at around 140 ?C, before it is impinged on a temperature-controlled substrate. For the for- mation of thin fi lms, the homogeneous particle formation process is highly undesirable since the
4、 adsorption of the particles on the substrate surface yields powdery and non-adherent fi lms. The homogeneous chemistry of the impinging fl ux can be controlled precisely by the inlet concentrations, temperature, and most importantly the residence time. The reactant stream A consisted of the prepare
5、d aqueous precursor solution for the Cu and In sources. The stream B consisted of aqueous sodium selenosulfi te solution. The fl ow rate of solution was fi xed in 1 ml/s and the time of impinging was fi xed at 7 min. The details of the CFM deposition procedure have been described in our previous pap
6、ers 813. In order to improve the crystallinity of the fi lms, the as-deposited CuInSe2 fi lms were annealed at 400 ?C under a nitrogen atmo- spheric condition. 2.3. Characterizations of CuInSe2 thin fi lms The optical band gap, surface morphology, crystalline structure, and chemical binding informat
7、ion of the prepared CuInSe2thin fi lms were analyzed using UVvisible spectrophotometer (Ocean Optics, USB-4000 optic spectrometer), scanning electron micro- scope (SEM, Hitachi S-4800), thin fi lm X-ray diffraction spectrom- eter (XRD, Panalytical MPD for thin fi lm), and X-ray photoelectron spectro
8、scopy (XPS, ESCALAB, 250 XPS spectrometer). 3. Results and discussion 3.1. Structural characterization The crystal structure and crystallographic orientation of the polycrystalline CuInSe2 thin fi lms deposited by the CFM method was determined by the analysis of XRD spectra in comparison with the JC
9、PDS data and literatures. Fig. 1 shows X-ray diffraction pat- terns of the CuInSe2 thin fi lms deposited by varying the indium re- agent concentration in the precursor solution. The spectrum (a) represents the XRD pattern of the as-deposited CuInSe2 fi lm pre- pared using a precursor solution contai
10、ning 0.025 M aqueous InCl3. The major characteristic diffraction lines (1 1 2), (2 1 1), and (2 0 4), which indicate the formation of CuInSe2ternary compound, are observed even in the as-deposited fi lm although their intensity is very weak. The XRD spectra in Fig. 1bd present the diffraction patter
11、ns of the thermally treated CuInSe2 fi lms, which were pre- pared from 0.005 M, 0.010 M, and 0.025 M InCl3, respectively. More intensive peaks were observed after thermal annealing as shown in Fig. 1. This result indicates that more crystalline CuInSe2 thin fi lms were formed when the molar concentr
12、ation of InCl3in- creases. The fi lm deposited from a solution with 0.025 M of InCl3 shows the best crystallinity. The diffraction peaks at 2h = 26.65?, 35.54?, 44.184?, 52.433?, and 62.668? correspond to the (1 1 2), (2 1 1), (2 0 4), (3 1 2), and (3 2 3) crystallographic planes of the tetragonal C
13、uInSe2structure, respectively. These X-ray diffraction peaks are in good agreement with the data of JCPDS 87-2265 for tetragonal chalcopyrite phase only except appearance of a CuIn metal alloy peak. A characteristic peak located at 2h = 41.93? was observed in the XRD pattern and it was identifi ed a
14、s the CuIn metal alloy line belonging to Cu4In and Cu9In4systems 14. The alloy line becomes more intensive as the InCl3content increases. The pres- ence of microregions containing unreacted Cu and In elements could be the cause for the observed Cu4In and Cu9In4alloy diffrac- tion lines 15. If indium
15、 remains unreacted in the as-deposited fi lms, the selenization of Cu can be interrupted by a reaction be- tween In and Cu prior to the occurrence of selenization. It is in- ferred that the unreacted indium leads to the formation of the Cu4In and Cu9In4alloy during the thermal treatment process. Fro
16、m Fig. 1. X-ray diffraction patterns of the CuInSe2 thin fi lms annealed at 400 ?C for 1 h: (a) the as-deposited, (b) 0.005 M of InCl3, (c) 0.010 M of InCl3and (d) 0.025 M of InCl3in the precursor solution of In source. Fig. 2. UVvis absorption spectra of the CuInSe2 fi lm deposited with the precurs
17、or solution containing 0.025 M of InCl3and its estimated optical band gap: (a) the as- deposited and (b) the annealed at 400 ?C. S384C.R. Kim et al./Current Applied Physics 10 (2010) S383S386 the XRD analysis, it was found that the crystal growth of the as- deposited and the annealed fi lms are affe
18、cted by the molar concen- tration of indium source. 3.2. Optical band gap Optical band gaps of CuInSe2 thin fi lms were measured in a vis- ible range of 300800 nm using UVvisible spectrophotometer. In general, the optical band gap of the prepared fi lm can be obtained by extrapolating the straight l
19、ine portion of the plot of (ahm)2 against hm to the energy axis for zero absorption coeffi cient,a. Fig. 2 shows a plot of (ahm)2against hmfor the CuInSe2 fi lm being prepared with 0.025 M InCl3. Its optical band gap energy was esti- mated to be ?1.54 eV for the as-deposited CuInSe2 thin fi lm and ?
20、1.25 eV for the thermally treated fi lm at 400 ?C. The chalcopyrite CuInSe2 fi lms were reported to have an optical band gap in the range of 0.981.04 eV, depending on the Cu/In ratio 16. The high- er optical band gap value obtained in this work might be attributed to the quantum size effect, commonl
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