Lithium-antimony co-doping induced morphology transition in spray deposited SnO2 thin films
Introduction
Transparent conducting oxides (TCOs) should have salient features like high conductivity, high optical transparency and good stability to be employed as transparent conducting electrodes (TCEs) in various optoelectronic devices [1,2]. Deposition of a TCE film with high electrical conductivity and optical transparency via facile deposition method is necessary for its usage as a component in efficient display and energy harvesting devices. To date, binary oxides like ZnO [3], SnO2 [4], WO3 [5], In2O3 [6], TiO2 [7], and ternary oxides like Zn2SnO4 [8], Cd2SnO4 [9], and BaSnO3 [10] have been explored for alternative TCO system by appropriate doping. Among the family of binary oxides, n-type tin oxide (SnO2) has been considered as one of the best host materials since its physical and chemical properties can be tuned by doping it with several metallic impurities [11]. The undoped SnO2 films show very low electrical conductivity and optical transmittance [12], whereas donor doped SnO2 films exhibit higher carrier concentration and improved mobility, thereby offering properties beneficial for optoelectronic device applications [11]. Donor doped SnO2 films have been extensively studied over the past two decades. Smaller crystallite size, smooth surface morphology, high optical transmittance and excellent electrical conductivity properties offer better device performance [13]. Precise control over surface features of donor doped SnO2 films also plays a critical role in device performance. In addition, conductivity of the donor doped SnO2 films is improved in the presence of optimal oxygen vacancy defects, which is also eventually necessary for better device performance [14]. The donor doped SnO2 materials such as fluorine-doped tin oxide (FTO), antimony (Sb) doped tin oxide (ATO), aluminum doped zinc oxide (AZO), along with indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO) show promising TCO properties [11,[15], [16], [17]].
Among the donor doped SnO2 materials, Sb doped SnO2 (ATO) thin film is explored extensively for alternative TCO application due to its better optoelectronic properties [18]. It should also be noted that ATO film usually has a grey tinge which degrades its optical properties. To overcome this issue, ATO film is co-doped with suitable elements like F, Mn, Ba, etc. [19], [20], [21], [22], [23]. Low resistivity values of 4.0 × 10−3 Ω cm and 3.4 × 10−3 Ω cm have been reported for ATO films deposited using co-sputtering and plasma-assisted molecular beam epitaxy methods, respectively [24,25]. However, the reported transmittance values of those films are relatively lower than those for commercially available FTO/ITO materials. The co-doping effect of SnO2 sample has a strong correlation to its TCE properties [26]. An early study by Shanthi et al. showed that the F:Sb co-doped SnO2 sample has better transmittance and good conductivity when compared to Sb-doped SnO2 sample [27]. They proposed that this is mainly caused by the improved mobility of the sample due to co-doping effect of F and Sb into the SnO2 lattice. Recently, Ba has been co-doped with Sb into SnO2 host to overcome the grey tinge problem and is found to enhance the electrical and optical properties [22]. However, few research groups have explored Li doping into SnO2 lattice, and it has been reported that the spray deposited Li-doped SnO2 films exhibit low sheet resistance and good optical transmittance due to better surface and structural properties [28], [29], [30]. It is reported that alkali metals (Li, Na) effectively promote oxygen vacancies in the metal oxide system [31]. It has also been reported that Li occupying the interstitial sites of ZnO leads to change in the conduction type, i.e., from n- to p-type as a function of increasing Li concentration [32]. However, at high concentration, reversal of conduction type is observed which is attributed to self-compensation effect [32]. Moreover, presence of oxygen vacancies leading to improved electrical conductivity is also reported [33]. It is also identified that Li can improve the ionic conductivity due to 2s1 electron in its valence shell [31].
Doping SnO2 thin films with either Li or Sb for TCE applications has been investigated by researchers [18,30]. However, there are no reports available on the investigation of Li (varying concentration) and 5 wt.% Sb co-doped SnO2 thin films deposited using spray pyrolysis for alternative TCE applications. With this motivation, it is intended to explore the effect of Li-Sb co-doping into the SnO2 host material. In the present work, thin films of undoped SnO2, 5 wt.% Sb doped SnO2 (ATO), and Sb (5 wt.%): Li (1, 3, and 5 wt.%) co-doped SnO2 (LATO) are deposited onto glass substrates using spray pyrolysis method. The deposited films are studied for their structural, surface morphological, optical and temperature dependent electrical properties. The obtained results are discussed in detail in the forthcoming sections.
Section snippets
Spray deposition of un-doped, Sb doped and Li-Sb co-doped SnO2 thin films
Stoichiometric amount of SnCl2.2H2O, SbCl3 and LiCl precursors were dissolved thoroughly in 250 mL of ethylene glycol. De-ionized water (50 mL) along with 2 mL of HCl (to make a transparent solution) was also added to the above mixture. Microscopic glass slides [75 mm (l) × 25 mm (w) × 1.2 mm (t)] were used as substrates after cleaning ultrasonically in mild acid and de-ionized water to remove traces of grease or oil adhered onto the surface. The substrate temperature maintained at 350 ˚C was
X-ray diffraction analysis
The XRD patterns of TO, ATO, LATO1, LATO3, and LATO5 thin films show polycrystalline nature (Fig. 1). All the peaks can be indexed to the tetragonal SnO2 structure matching well with the joint committee on powder diffraction standards (JCPDS) card No. 41-1445 [37]. The plausible secondary phase peaks of SnO, Sn2O3, Sb2O3, and Li2O are not observed in the XRD patterns, indicating phase purity of the films. However, significant variation in intensity as a function of doping is observed in the XRD
Conclusion
In summary, undoped SnO2, ATO, and LATO thin films were deposited on glass substrates by facile spray pyrolysis method. The XRD patterns confirm the polycrystalline nature with tetragonal crystal structure. The films are textured along the (110) plane direction. The SEM analysis clearly indicates the change in surface morphology from dendritic to cuboid shape upon Sb-Li co-doping into the SnO2 system. The observed changeover of surface morphology from dendritic to cuboid shape is the main
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The author UD acknowledges the Dr. D. S. Kothari Post-Doctoral Fellowship (Project No: F.4-2/2006 (BSR)/PH/17-18/0098) for the financial support. The author MK thanks the Science & Engineering Research Board (SERB), Department of Science and Technology, Government of India, for the award of National Post Doctoral Fellowship (File Number: PDF/2019/002766).
References (75)
- et al.
Review on electrochromic property for WO3 thin films using different deposition techniques
Mater. Today Proc.
(2016) - et al.
Electronic structure analysis of Sb-doped BaSnO3
Mater. Sci. Eng. B Solid-State Mater. Adv. Technol.
(2010) - et al.
Surface and bulk properties of sputter deposited undoped and Sb-doped SnO2 thin films
Sens. Actuators B
(2009) - et al.
Structural and optical properties of Zn-doped SnO2 films prepared by DC and RF magnetron co-sputtering
Superlattices Microstruct.
(2016) - et al.
Weak localization and electron-electron scattering in fluorine-doped SnO2 random nanobelt thin films
J. Phys. Chem. Solids
(2014) - et al.
Influence of simultaneous cationic (Mn) and anionic (F) doping on the magnetic and certain other properties of SnO2 thin films
Surf. Interfaces
(2017) - et al.
Electrochemical mineralization of perfluorooctane sulfonate by novel F and Sb co-doped Ti/SnO2 electrode containing Sn-Sb interlayer
Chem. Eng. J.
(2017) - et al.
Improvement of electrochemical performance of tin dioxide electrodes through manganese and antimony co-doping
J. Electroanal. Chem.
(2016) - et al.
Epitaxial Sb-doped SnO2and Sn-doped In2O3transparent conducting oxide contacts on GaN-based light emitting diodes
Thin Solid Films
(2016) - et al.
Study of structural, electrical and photoconductive properties of F and P co-doped SnO2 transparent semiconducting thin film deposited by spray pyrolysis
Mater. Sci. Semicond. Process
(2015)
Effect of Li doping on the structural, optical and electrical properties of spray deposited SnO2thin films
Thin Solid Films
Oxygen gas sensing properties of undoped and Li-doped SnO2 thin films
Sensors Actuators B. Chem.
Alkaline earth metal doped tin oxide as a novel oxygen storage material
Mater. Res. Bull.
Versatility of chemical spray pyrolysis technique
Mater. Chem. Phys.
SnO2: a comprehensive review on structures and gas sensors
Prog. Mater. Sci.
Preferred orientations in polycrystalline SnO2films grown by atmospheric pressure chemical vapor deposition
Thin Solid Films
Substrate temperature dependent physical properties of spray deposited antimony-doped SnO2 thin films
Thin Solid Films
Initial growth of SnO2 thin film on the glass substrate deposited by the spray pyrolysis technique
Thin Solid Films
Effect of Ta doping on the characteristic features of spray-coated SnO2
Thin Solid Films
Sensing properties of sprayed antimony doped tin oxide thin films: solution molarity
J. Alloys Compd.
Effect of F and Nb co-doping on structural, electrical and optical properties of spray deposited tin oxide thin films
Thin Solid Films
Structural features, low-temperature luminescence properties of Li-doped SnO2 nanobelts and their transitional temperature
J. Lumin.
High figure of merit transparent conducting Sb-doped SnO2 thin films prepared via ultrasonic spray pyrolysis
J. Alloys Compd.
Low-temperature solution-processed Li-doped SnO2 as an effective electron transporting layer for high-performance flexible and wearable perovskite solar cells
Nano Energy
Structural and photoluminescence properties of SnO2 obtained by thermal oxidation of evaporated Sn thin films
Curr. Appl. Phys.
Low-temperature solution-processed ionic liquid modified SnO2as an excellent electron transport layer for inverted organic solar cells
Sol. Energy Mater. Sol. Cells
Effect of film thickness on the structural, optical and electrical properties of SnO 2 : F thin films prepared by spray ultrasonic for solar cells applications
Superlattices Microstruct.
Structural and optoelectronic properties of antimony incorporated tin oxide thin films
J. Alloys Compd.
Structural, optical and electrical properties studies of ultrasonically deposited tin oxide (SnO2) thin films with different substrate temperatures
Superlattices Microstruct.
Indium-free large area Nb-doped SnO2 thin film as an alternative transparent conducting electrode
Ceram. Int.
Effect of fluorine doping on highly transparent conductive spray deposited nanocrystalline tin oxide thin film
Appl. Surf. Sci.
Nano-sized indium-free MTO/Ag/MTO transparent conductingelectrode prepared by RF sputtering at room temperature for organicphotovoltaic cells
Sol. Energy Mater Sol. Cells
Metal oxides for optoelectronic applications
Nat. Mater.
Transparent conducting oxides—an up-to-date overview
Materials (Basel)
ZnO devices and applications: a review of current status and future prospects
Proc. IEEE
Review on the Application of SnO2 in Perovskite Solar Cells
Adv. Funct. Mater.
Amorphous and crystalline In2O3-based transparent conducting films for photovoltaics
Phys. Status Solidi Appl. Mater. Sci.
Cited by (12)
Effect of anionic bromine doping on the structural, optical and electrical properties of spray-pyrolyzed SnO<inf>2</inf> thin films
2022, Materials Science and Engineering: BCitation Excerpt :Although the transparent conducting properties of widely used fluorine (F)-doped thin films are superior compared to that of Br-doped thin films, Br is chosen as dopant in the present work due to its higher chemical stability compared to F. Moreover, there are hardly any investigations on the structural, morphological, optical and temperature- dependent electrical properties of bromine-doped SnO2 thin films for potential use as TCEs, which serves as motivation for the present work. A 5 wt% of Br dopant concentration is chosen for the present investigation based on our previous work on Li:Sb co-doped SnO2 films wherein 5 wt% Li and 5 wt% Sb in SnO2 showed better properties compared to other films [42]. In addition, there are reports on several other dopants where ≅ 5 wt% concentration has proved to be beneficial in improving the optoelectronic properties [43,44].
Highlights on the structural, optical, and optoelectrical properties of novel InSbO<inf>3</inf> thin films synthesized by chemical bath deposition
2022, Journal of Non-Crystalline SolidsCitation Excerpt :In addition, the TOs thin films based on tin or zinc elements like aluminum zinc oxide, indium tin oxide, and antimony tin oxide are important materials for producing transparent conductive oxides (TCOs). This renders to their high electrical conductivity and high optical transmittance which enables exploiting them in worthy implementations in solar cells, optoelectronic devices, and light-emitting diodes [12–14]. Moreover, the ternary oxides based on copper metal oxides CuMO2 (Delafossite compounds M=Al, Mn, and Cr) are important materials for producing good p-type delafossite thin films [15,16].
Annealing induced morphology evolution and phase transition in SnO<inf>x</inf> thin films grown by e-beam evaporation method
2022, Inorganic Chemistry CommunicationsCitation Excerpt :The excitation binding energy of SnO2 around 130 meV and band gap energies (Eg) correspond to ∼3.1–4.0 eV which is sufficiently high to avoid the absorption of light over most of the solar spectra, thereby leading to high optical transparency [14–16]. A large number of deposition methods have been used to obtain SnOx thin films, such as pulsed laser deposition[17], spray pyrolysis [18], vacuum evaporation [11], gas-phase deposition [19] CVD [20], chemical bath deposition (CBD) [21], spin-coating [22] magnetron sputtering [5,13], sol-gel [23] and atomic layer deposition[4], and electron beam evaporation (EBE) [24–27] are used for the growth of SnOx thin films. Among all of them, e-beam evaporation method is quite suitable to obtain dense, homogeneous and a fine-quality SnOx thin films in a very short time.