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Annealing Effect on (SnO₂)0.3:(In₂O₃)0.7 Solar Cell Prepared by PLD Technique

Abdulmajeed E. Ibrahim, Kadhem A. Aadim, Qutaibah A. Abduljabbar*

Department of Physics, University of Tikrit/College of Education

Abstract: Indium tin oxide (ITO) thin films were produced by Q- switched Nd:YAG laser with wavelength (1064 nm) has 800 mJ peak energy on In₂O3 :SnO2 target with 0.3 ratio on p-type Si and on porous Si to fabricated solar cell. The as deposited and annealed thin films on glass substrates were characterized by X-ray diffraction Atomic force microscopy (AFM), UV-visible absorbance and Hall effect measurements. Then the fabricated solar cells examined in the dark and under illumination for SnO₂:In₂O₃ /p-Si and SnO₂:In₂O₃/Psi/p-Si annealed and as deposited samples.

Keywords: solar cell, pulse laser, porous-Si

Citation: Abdulmajeed E. Ibrahim, Kadhem A. Aadim, Qutaibah A. Abduljabbar, Annealing Effect on (SnO₂)0.3:(In₂O₃)0.7 Solar Cell Prepared by PLD Technique. International Journal of Physics, 5 (4). 110-115. January 2017. doi:10.12691/ijp-5-4-2

1. Introduction

Now a day there are many techniques utilized to enhance solar cell efficiency enhance solar cells efficiency [1].

The generic solar cell is a structure consisting of two active layers, thin heavily doped top layer called the emitter or window layer and thick moderately doped bottom layer, called the base or absorber with opposite doping [2]. We need to study the optical, structural [3], morphological [4] and electrical properties for used material as window in solar cells on the side where light enters, to reach optimum efficiency [5]

X- ray diffraction used to characterize obtained films crystallinety. The dhkl spacing between crystals planes can deduced by X-ray diffraction using Bragg's law [6]

[picture] | (1)

where Ө is diffraction angle and λ is the used XRD wavelength.

Scherrer equation formula used to calculate crystalline size utilize the peaks broadening [7].

[picture] | (2)

Where λ is the x-ray wavelength for kα transition from Cu target (1.5406 Å), FWHM is full width at half maximum and θ is the angle of diffraction.

Several parameters are used to characterize solar cells. A solar cell under illumination is characterized by the following parameters: the Short-circuit current, the open-circuit voltage, the fill factor and the power conversion efficiency [8]. Fill Factor indicates the quality of current-voltage characteristics and it depends on the ability of charges to reach the electrodes which is governed by recombination processes. The full factor is directly affected by the values of the cell's series and shunt resistances [9]. The solar cell efficiency is the ratio for outcome power to incident light power density [10].

2. Experimental Part

A porous silicon structure is prepared by electrochemical etching of silicon substrate of (111) orientation with a resistivity (4 -10) Ω. cm and the etching cell is made of Teflon. The electrochemical cell used has two electrode configurations with a platinum electrode as cathode and silicon wafer as anode. The etching times is chosen to be 10 min and current (30) mA. The samples are dipped in (48%) concentration of (HF) acid in mixing ratio (1 : 1) HF: ethanol with the aid of diode laser source as an illumination sources. However, the addition of ethanol to HF eliminates hydrogen and ensures complete infiltration of HF solution which further improves the uniform distribution of porosity and thickness.

Figure 1. Schematic for porous silicon layer formation system

In₂O3 with purity (99.9 %) and SnO₂ powder purity (99.98 %) by FERAK company, England were mixed with In₂O₃:SnO₂ ratio 30 % in gate mortar to use it to make pellet target as a disk of 1.5cm diameter using hydraulic piston under pressure of 6 tons.

SnO₂: In₂O₃ thin films were prepared on glass, p-Si and porous-Si substrates by Q switched pulsed laser (Huafei Tongda Technology- DIAMOND-288 pattern EPLS) λ = 1064 nm with 800 mJ peak power inside a vacuum chamber at vacuum (10⁻³ Torr) using double stage rotary pump. The incident beam coming through a window making an angle of 45° with the target surface. The substrate is placed parallel target surface. The produced films were characterized by X-ray diffraction (XRD), DC conductivity, Hall effect measurements and UV-visible absorption

Metal electrodes of aluminum are formed both back surface of the Si wafer and top of the SnO₂:In₂O3 films by thermal evaporation, carried out at a pressure of (10-5 mbar) in a vacuum (Edwards Auto 306). Annealing at 773K for 2 hours to enhance the films properties and its adhesion.

I-V measurements were made for fabricated solar cell heterojunctions in case of dark and under illumination by Halogen lamp light Philips (120W) with 100 mW/cm² intensity using Keithley Digital Electrometer 616, voltmeter and D.C. power supply under reverse and forward bias voltage in the range (-2 to 2) Volt to study the effect of annealing and porous formation on solar cells efficiency.

3. Results and Discussion

Figure 2 shows the X-ray diffraction for as deposited In₂O₃:SnO2 with 0.3 ratio films deposited on glass substrates by pulse laser deposition and annealed at different temperatures (573, 673and 773) K. We can observe from this figure that as deposited film has amorphous structure at RT, while annealed one at 573 K, convert to polycrystalline structure, and with annealing at 673 K many peaks corresponding to In₂O₃ and one peaks for SnO₂. The crystallinety increase with increasing annealing to 773 K and their location shift toward higher values indicate on increase atomic backing with annealing. The FWHM decrease with increasing annealing temperature indicate on increasing G.S. Table 1 shows the experiment and the standard peaks from international center for diffraction data JCPD cards number (96-210-4744 and 96-101-0589).

Figure 2. XRD patterns for In₂O₃:SnO₂ thin films annealed at different temperature

Table 1. Comparison between experimental and standard XRD peak and calculated crystalline size

Figure 3 shows the AFM images and their granularity accumulation distribution for as deposited In₂O3 :SnO2 with 0.3 ratio films deposited on glass substrates by pulse laser deposition and annealed at different temperatures (573, 673and 773) K. This figure and Table 2 illustrate that the average diameter and RMS roughness decrease with increasing annealing temperature.

Figure 3. AFM images and their granularity accumulation distribution for In₂O₃ :SnO₂ =0.3 thin films deposited on glass substrate annealed at different temperature

Table 2. AFM parameters (Average Diameter, RMS roughness and Peak-peak distance) for pure for In₂O₃ :SnO₂ =0.3 thin films at different annealing temperature

Figure 4 shows the transmission spectra for In₂O₃:SnO₂ annealed at different temperature. It shows that the transmission increase with increasing annealing temperature reaching 85% in visible range, as a result of enhance the crystallinety [11].

Figure 4. the variation of transmission with wavelength for In₂O₃ :SnO₂ =0.3 thin films deposited on glass substrate annealed at different temperature

The optical energy gap values (Egopt) for In₂O₃:SnO₂ composite films at different annealing temperature have been determined by using Tauc equation as shown in Figure 5. From this figure seems that the energy gap increase from (2.8 to 3.7) eV with increasing annealing temperature as a result of increasing atomic backing with annealing [12].

Figure 5. Variation of (αhυ)² versus photon energy for In₂O₃ :SnO₂ thin films with different annealing

Hall effect measurements show that all films were (n-type). The variation of nH and μH with annealing temperature were shown in Table 3. The values of (n) increases with increasing annealing temperature reaching the maximum value at 673 K then decrease with more annealing. While the maximum value of electron mobility at 573 annealing temperature.

Table 3. Hall measurements of for In₂O₃:SnO₂ composite thin films with different annealing temperature

The I-V characteristics of SnO₂:In₂O₃/p-Si and SnO₂:In₂O₃/porous-Si solar cell with 0.3 In₂O₃ content, in the dark and under illumination using power densities equal to 100 mW/cm² with the applied forward and reverse bias voltage for RT and annealed at (773)K were shown in Figure 6. The solar cells parameters were shown in Table 4. This table shows that in general the annealed ones best than as deposited films and the samples deposited on porous Si best than that deposited on Si wafers.

Figure 6. I-V characteristics for SnO₂ :In₂O₃/P-Si and SnO₂ :In₂O₃/porous-Si heterojunction Solar Cell at RT and 773 K annealing temperatures in case of dark and under illumination

From the plot of the forward current (If) versus applied forward bias voltage (Vf), the ideality factor (β) is obtained according to the relation [13]

[picture] | (3)

where Is is the saturation current and it can be obtained by extrapolating the forward current curves to zero voltage.

Table 4. I-V Parameters for SnO₂ :In₂O₃/p-Si and SnO₂ :In₂O₃/porous-Si solar cell

4. Conclusions

The results of examination of In₂O₃ :SnO2 thin films deposited on glass substrates by XRD by pulse laser deposition show that annealing convert amorphous structure to polycrystalline structure with peaks corresponding to In₂O₃ and SnO₂. The crystallinety and the crystalline size increase with increasing annealing to 773 K.

The UV visible easements shows that the annealing leads to increase transparency and increase energy gap from 2.8 to 3.7 eV.

Hall effect measurements shows n-type for all films. The charge carrier concentration has maximum value at 673 K, while the maximum value of electron mobility at 573 annealing temperature.

The results for fabricated solar cells ( SnO₂:In₂O₃ /p-Si and SnO₂:In₂O₃/Psi/p-Si) by pulse laser deposition technique annealed and as deposited samples shows that the annealed ones best than as deposited films and the samples deposited on porous Si best than that deposited on Si wafers.

References

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[5]   | D.G. Parker and P. G. Say, “Indium tin oxide/GaAs photodiodes for millimetric-wave applications,” Electronics Letters, vol. 22, no. 23, pp. 1266-1267, (1986).
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[11]   | S. Chan, M. Li, H. Wei, S. Chen, and C. Kuo1, “The Effect of Annealing on Nanothick Indium Tin Oxide Transparent Conductive Films for Touch Sensors” Journal of Nanomaterials, Vol. 2015 (2015).
[12]   | ZnS Nanocrystals G. Muralia, D. Amaranatha, B. Poornaprakasha, R. Vijayalakshmia, N. Madhusudhana Rao, “Effect Of Annealing On Structural And Optical Properties Of” Optoelectronics And Advanced Materials , vol. 5, no. 9, 2011, p. 928-931.

[13]  
H. M. Zeyada, M. M. El-Nahass, I. K. El-Zawawi, and E. M. El-Menyawy, “Characterization of 2-(2,3-dihydro-1,5- dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl) acetonitrile and ZnO nano-crystallite structure thin films for application in solar cells,” The European Physical Journal, vol. 49, p. 10301, (2010).