In this paper, ZnO-based nanostructured films were prepared by hydrothermal method on ZnO seed layers obtained 
by sol-gel method and AZO transparent conductive glass. X RD, SEM, sheet resistance test, transmittance and haze spectra were used 
to characterize the structure, morphology, optoelectronic properties and light trapping abilities of the films. The effects of seed layer 
concentration and hydrothermal growth temperature on the characteristics of ZnO-based nanostructured fi lms were studied, and the prepared 
fi lms had light trapping eff ects and high total transmittance in the visible light region

Liu, Jian

Song, Zhaoying

Wang, Ying

Yan, Jiaming

English

Electronics Science Technology and Application (E-Journal)

166 2023 Volume 10 Issue 4Preparation and properties of ZnO-based nanostructured films with	light	trapping	eff	ectsJian Liu, Ying Wang*, Jiaming Yan, Zhaoying SongSchool of Science, University of Science and Technology Liaoning, Anshan 114051, ChinaA bstract: In this paper, ZnO-based nanostructured films were prepared by hydrothermal method on ZnO seed layers obtained by sol-gel method and AZO transparent conductive glass. X RD, SEM, sheet resistance test, transmittance and haze spectra were used to characterize the structure, morphology, optoelectronic properties and light trapping abilities of the films. The effects of seed layer concentration and hydrothermal growth temperature on the characteristics of ZnO-based nanostructured fi lms were studied, and the prepared fi lms had light trapping eff ects and high total transmittance in the visible light region.Key words: ZnO-based thin fi lms; Nanostructure; Optoelectronic properties; Light trapping eff ect1. IntroductionTransparent conductive oxide films have been widely used in solar cells because of their excellent optoelectronic properties. The introduction of the light trapping structures in the fi lms as the front electrodes of the solar cell can increase the path of the incident light in the absorption layer and eff ectively improve the conversion effi  ciency of the cells.Z nO has the advantages of wide band gap and high transmittance in the visible region. Doping Al, Ga and other elements can improve the electrical conductivity of ZnO. ZnO-based nanostructured fi lms with light trapping eff ects can be obtained by various methods. And the sol-gel method, hydrothermal method and other wet chemical methods have the advantages of simple technology, low cost and low growth temperature.In this paper, ZnO-based nanostructured fi lms were prepared by hydrothermal method on ZnO seed layers obtained by sol-gel method and AZO transparent conductive glass. The morphology, structure, optoelectronic properties and light trapping abilities of ZnO-based nanostructured fi lms prepared at diff erent seed layer concentrations and hydrothermal growth temperatures were studied.2. Experimental2.1 Preparation of ZnO nanostructured fi lmsZnO seed layer solutions with concentrations of 0.005 M, 0.015 M, 0.02 M and 0.03 M were prepared by dissolving Zn(CH3COO)2·2H2O in ethanol and were aged for 12 h. The seed layer solutions were evenly coated on the glass substrate by spin coating method. And then the samples were placed in the oven at 100℃. The above process was repeated for 8 times. The samples were annealed at 350°C for 30 min. Subsequently, ZnO nanostructured fi lms were grown by hydrothermal method. Zn(CH3COO)2·2H2O and C6H12N4 aqueous solution at equal concentration of 0.03 M were mixed and s tirred at room temperature and poured into a T efl on-lined autoclave apparatus containing seed layer samples. After sealing, the samples were grown in an oven at 90℃ for 2 h. Finally, the samples were rinsed with deionized water and dried.2.2 Preparation of AZO nanostructured fi lmsAZO nanostructured films were grown on AZO transparent conductive glass by hydrothermal method. Zn(CH3COO)2·2H2O and C6H12N4 with molar concentrations of 0.1 M were used as precursors, and Al(NO3)3·9H2O was added as doping source (Al: 2 mol%). After stirring and dissolving, the solutions were poured into the Tefl on-lined autoclave apparatus for hydrothermal growth in the oven at diff erent temperatures (70℃, 80℃, 90℃, 100℃) for 3 h. Finally, the samples were rinsed with deionized water and dried.2.3 CharacterizationThe morphology of the films was analyzed by field-emission scanning electron microscopy. The crystal structure of the films was measured by X-ray diff raction (XRD). The transmittance and haze spectra of the samples were measured by U V-Vis-NIR spectrophotometer with an integrating sphere. The sheet resistance of the fi lms was measured by an RTS-8 four-point probe instrument.3. Results and discussion3.1 ZnO nanostructured fi lmsFig. 1 shows the SEM images of ZnO fi lms prepared under diff erent seed layer concentrations. When the seed layer concentration is 0.005 M, the surface of the fi lm shows the rough blocky structures. This may be because the concentration of the seed layer is too low, which aff ects the nucleation process of ZnO seed. W ith the increase of the seed layer concentration, hexagonal ZnO nanorod structures in the direction perpendicular to the substrate can be seen obviously. And there are more gaps among the nanorods. When the seed layer concentration is increased to 0.03 M, the nanorod structure become denser. In addition, it can be seen from Fig. 1(b)-(d) that the ZnO nanorods of all samples are uniform in size and smaller in diameter, and the surface of the fi lms is denser.1672023 Volume 10 Issue 4Fig.	1	SEM	images	of	ZnO	nanostructured	fi	lms	at	diff	erent	seed	layer	concentrations:(a) 0.005 M, (b) 0.015 M, (c) 0.02 M and (d) 0.03 MFig. 2(a) shows the total transmittance spectra of all ZnO nanostructured fi lms. The average total transmittance of all ZnO fi lms reac hes 90% and increases with the increase of seed layer concentration. At the same time, all the samples have a steep absorption edge in the UV region. Fig. 2(b) shows the haze spectra of ZnO fi lms at diff erent seed layer concentrations. The haze values of the fi lms are all greater than 0 in the visible light region, indicating that the prepared ZnO nanostructured fi lms have light trapping eff ects. When the concentration of seed layer is 0.02 M, the haze value of the fi lms reaches 0.07 at 550nm. The light trapping ability of ZnO fi lms is closely related to the surface microstructure. The large tilt  angle of nanorods leads to more gaps among the nanorods, which will enhance the light scattering and the light trapping abilities.(a)                                                                                      (b)Fig.	2	(a)	Total	transmittance	spectra	and	(b)	haze	spectra	of	ZnO	nanostructured	fi	lms	at	diff	erent	seed	layer	concentrations.3.2 A ZO nanostructured fi lmsFig.	3	XRD	patterns	of	AZO	fi	lms	at	diff	erent	hydrothermal	temperatures.Fig. 3 shows the XRD patterns of AZO films under different hydrothermal temperatures. All the films have a strong and weak diff raction peak at 2θ of 34.4° and 72.5°, corresponding to the (002) and (004) crystal plane of hexagonal wurtzite ZnO, respectively. The AZO nanostructures grow preferentially along the c-axis perpendicular to the substrate. The intensity of (002) peak is increased with the increase of hydrothermal temperature, indicating that the crystalline quality of the fi lms is improved with the increase of hydrothermal temperature.Fig. 4 shows the SEM images of AZO nanostructured fi lms under diff erent hydrothermal temperatures. At 70℃, only a small number of irregular hexagonal AZO nanorod structures can be seen on the surface of the fi lm. This may be due to the relatively slow nucleation and growth rate of AZO nanorods at low temperature. As the growth temperature is increased gradually, the hexagonal AZO nanorods are clearly visible and increased. It can b e seen from the above results that with the increase of growth temperature, the morphology of ZnO changes from a network-like structure to a nanorod-like structure. At 100℃, more gaps are observed among the nanorods, as shown in Fig. 4(d).168 2023 Volume 10 Issue 4Fig.	4	SEM	images	of	AZO	nanostructured	fi	lms	at	diff	erent	hydrothermal	temperatures:(a)70℃,	(b)80℃,	(c)90℃,	(d)100℃Fig. 5(a) shows the total transmittance spectra of all AZO nanostructured fi lms. All fi lms have a high average total transmittance of 80% in visible light region. As the hydrothermal temperature increases, the steep absorption edge is redshifted in the UV region. Fig. 5(b) shows the haze spectra of all AZO nanostructured fi lms. The haze value increases with the increase of hydrothermal temperature. Compared with the network-like AZO fi lms, the nanorod-like AZO fi lms have higher haze value. It can be seen from SEM and haze spectra that the haze value increases with the appearance of a large number of nanorod structures on the surface of the samples. When the hydrothermal growth temperature is 100℃, there are more gaps among the nanorods on the surface of AZO nanostructured fi lms, which is benefi cial for improving the light trapping abilities of the fi lms. And the high haze value of 0.14 is obtained at 550 nm. Fig. 5 (c) shows the sheet resistance of AZO nanostructured fi lms at diff erent hydrothermal temperatures. When the hydrothermal temperature rises from 70 ℃ to 90 ℃, the sheet resistance value of the fi lms is about 70-90 Ω/sq, which is relatively low. When the hydrothermal temperature is 100°C, the fi lm has a higher sheet resistance value of about 160 Ω/sq than the other three samples.(a)                                                                           (b)                                                                  (c)Fig.	5	(a)	Total	transmittance	spectra,	(b)	haze	spectra	and	(c)	sheet	resistance	of	AZO	nanostructured	fi	lms	at	diff	erent	hydrothermal temperatures.4. ConclusionsIn this paper, ZnO-based nanostructured fi lms with light trapping eff ects were prepared by hydrothermal method on ZnO seed layers obtained by sol-gel method and AZO transparent conductive glass. XRD results showed that the prepared ZnO-based nanostructured fi lms were typical hexagonal wurtzite structures. The average total transmittance of all the samples in the visible light range was more than 80%. The morphology of ZnO nanostructured fi lms varied with the concentration of seed layers. The ZnO nanostructured fi lms prepared at the seed layer concentration of 0.02 M had the highest haze value. With the increase of hydrothermal temperature, the surface morphology of AZO nanostructured fi lms changed from network-like to nanorod-like structures. The AZO fi lms prepared at 100℃ had higher haze value. In addition, AZO nanostructured fi lms also exhibited low sheet resistance.References[1]S Abdellatif, K Kirah, R Ghannam, et al. Enhancing the absorption capabilities of thin-fi lm solar cells using sandwiched light trapping structures[J]. Applied Optics, 2015, 54(17): 5534-5541.[2]M Choi, D Lim, J Kim, et al. Characteristics of nano-laminated Al-doped ZnO (AZO) multilayers[J]. Journal of Nanoscience and Nanotechnology, 2016, 16(11): 11715-11721.[3]M Skompska, K Zarebska. Electrodeposition of ZnO nanorod arrays on transparent conducting substrates-a review[J]. Electrochimica Acta, 2014, 127: 467-488.[4]Y Wang, D Q Hu, H B Jia, et al. Novel double-textured ZnO:Al transparent conducting fi lms with high haze value[J]. Materials Letters, 2017, 208: 89-91.[5]C Shan, M Zhao, D Jiang, et al. Improved responsivity performance of ZnO fi lm ultraviolet photodetectors by vertical arrays ZnO nanowires with light trapping eff ect[J]. Nanotechnology, 2019, 30(30): 305703.*Corresponding author: Ying Wang

Preparation and properties of ZnO-based nanostructured films 
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Preparation and properties of ZnO-based nanostructured films with light trapping eff ects

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