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Article

Preparation and Characterization of Cu and Al Doped ZnO Thin Films for Solar Cell Applications

by
Mir Waqas Alam
1,*,
Mohd Zahid Ansari
2,
Muhammad Aamir
3,
Mir Waheed-Ur-Rehman
4,
Nazish Parveen
5 and
Sajid Ali Ansari
1,*
1
Department of Physics, College of Science, King Faisal University, Al-Hassa 31982, Saudi Arabia
2
School of Materials Science and Engineering, Yeungnam University, Gyeongsan 712749, Korea
3
Department of Basic Science, Preparatory Year Deanship, King Faisal University, P.O. Box 400, Hofuf, Al-Hassa 31982, Saudi Arabia
4
Nanoscience and Nano Technology Unit, Department of Physics, Islamia College of Science and Commerce, Hawal, Srinagar 190001, India
5
Deparment of Chemistry, College of Science, King Faisal University, Al-Hassa 31982, Saudi Arabia
*
Authors to whom correspondence should be addressed.
Crystals 2022, 12(2), 128; https://doi.org/10.3390/cryst12020128
Submission received: 17 December 2021 / Revised: 4 January 2022 / Accepted: 14 January 2022 / Published: 18 January 2022
(This article belongs to the Section Materials for Energy Applications)
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Versions Notes

Abstract

:
The Al- and Cu-doped ZnO nanostructured films in this study were deposited using a sputtering technique. Investigations based on X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Hall effect measurements, and optical transmission spectroscopy was performed to analyze the structural, electrical, and optical characteristics of the prepared Al–ZnO and Cu–ZnO nanostructured films. The analyses show that doping results in enhanced conductivity as well as improved mobility in Al–ZnO and Cu–ZnO films in comparison to pure ZnO films. The Al- and Cu-doped ZnO films exhibited low resistivity (2.9 × 10−4 Ω cm for Al–ZnO and 1.7 × 10−4 Ω cm for Cu–ZnO) along with an average transmittance of around 80% in the visible spectrum. Moreover, the optical bandgaps of undoped ZnO, Al–ZnO, and Cu–ZnO nanostructures were observed as 3.3, 3.28, and 3.24 eV, respectively. Finally, solar cells were assembled by employing ZnO nanostructured thin films as photoelectrodes, resulting in efficiencies of 0.492% and 0.559% for Al–ZnO- and Cu–ZnO-based solar cells, respectively.

1. Introduction

In the recent past, solar cells have garnered immense interest as the most promising solution to the twin crises of energy shortage and environmental deterioration due to their significant power conversion efficiency (PCE), sustainability, and low cost [1,2]. Nevertheless, the current values of PCE are not satisfactory for the widespread application of solar cells. One of the critical components, which governs the efficiency of a solar cell, is the electrode material. Among the most widely employed metal oxides for photoelectrodes (i.e., zinc oxide (ZnO) and titanium oxide (TiO2)), ZnO is particularly attractive because of its larger bandgap (~3.37 eV), higher excitonic binding energies (~60 meV) at room temperature, and higher electron mobility than TiO2. Further, besides being inexpensive and environmentally benign, the electrons of ZnO electrodes demonstrate a longer lifetime in comparison to those of TiO2 electrodes [3]. As a result, nanostructured ZnO thin films have been extensively employed in gas sensors [4], solar cells [5], and photocatalysts [6]. Doped ZnO is an attractive electrode material for solar cell applications due to enhanced electrical and optical properties, which mainly arise from doping-induced bandgap modification. In the present article, we discuss the fabrication of transparent conducting aluminum- and copper-doped zinc oxide (ZnO) nanostructures, preferably oriented in (101) direction, via RF sputtering for possible application in solar cells. In addition, the ability to tune the bandgap by simply varying the electron affinity yields further opportunities to enhance the performance of solar cells [7].
Many techniques for obtaining high-quality ZnO nanostructured films have been explored, including chemical vapor deposition (CVD) [8], metal-organic chemical vapor deposition (MOCVD) [9], radiofrequency (RF) sputtering [10], and chemical precipitation [11]. Of these, the RF or DC magnetron sputtering methods offer various merits over the other techniques. The advantages of sputtering include low deposition temperature, fast deposition rates, simple design, cost-effectiveness, and the widespread availability of this deposition technique for growing high-quality films with great uniformity, high packing density, and strong adhesion between the substrate and the film even at fast growth rates [12]. For example, Nomoto et al. [13] and Hirahara et al. [14] deposited high-quality Al-doped ZnO films via RF sputtering at relatively lower temperatures.
Nevertheless, the limited conductivity and low carrier concentration are the most frequently encountered problems with ZnO thin films, which eventually reduce the device efficiency [1]. An important strategy to improve the electron transport in ZnO involves the partial substitution of zinc (Zn) ions with different metal ions [15]. In this regard, the group III elements, such as Al, In, Ga, etc., are extensively explored as n-type dopants in ZnO. Of these, Al is the most widely used dopant to obtain n-type ZnO with high conductivity, high crystal quality, and good optical properties [16]. For instance, Lee et al. [17] reported Al–ZnO thin films deposited over glass substrate via RF sputtering having a low resistivity value of 6.2 × 10−4 Ω cm and ~80% average transmittance. Similarly, Wang et al. [18] and Lin et al. [19] prepared Al–ZnO films by simultaneously using non-reactive magnetron sputtering and RF magnetron sputtering. The prepared doped thin films showed resistivity values of 1.4 × 10−3 and 8.43 × 10−3 Ω cm, respectively. The group of Iwantono [20] reported greatly enhanced charge transport in Au-decorated ZnO nanorods as photoanode.
Additionally, the elements of group I and group V, such as Li, Na, K, N, P, As, Cu, etc., have also been incorporated as p-type dopants within a ZnO lattice [21]. Of these elements, Cu appears to be the most promising doping species, since it can yield either n-type or p-type doping inside a ZnO matrix, depending upon the synthetic conditions. For instance, Park et al. [22] theoretically predicted p-type behavior for the Cu-doped ZnO. On the contrary, Buchholz et al. [23], in a later study, observed both p- as well as n-type behaviors in Cu–ZnO structures. Incorporating Cu within the structure of ZnO results in modification of absorption as well as other physicochemical properties of ZnO due to the different electronic configurations and the atomic sizes of Zn and Cu. It has been observed that Cu enters the lattice of ZnO via substitution as deep acceptors along with an adjacent oxygen vacancy [24]. Additionally, the surface morphology of the prepared ZnO nanostructures was found to be significantly affected by the addition of Cu. As an example, Raja et al. [25] and Aravind et al. [26] synthesized Cu-doped ZnO nanorods. The authors reported that the introduction of Cu into ZnO nanostructures changed the morphology, resulting in uniformly distributed clusters of elongated nanorods.
Presently, improving the performance of ZnO-based solar cells by incorporating various metal ions has become a major research area. From this perspective, we present the deposition of undoped ZnO, Al-doped ZnO, and Cu-doped ZnO nanostructured films via room temperature radiofrequency (RF) sputtering. The electrical properties of the prepared thin films were measured including resistivity, carrier concentration, and Hall mobility. In addition, the optical characteristics of the obtained films were explored via UV–Vis spectroscopy. Finally, the suitability of both Al–ZnO, and Cu–ZnO nanostructures for use as photoelectrodes in solar cells was analyzed.

2. Materials and Methods

2.1. Materials

Zinc oxide (ZnO; >99%), zinc oxide with aluminum (Al–ZnO; >99%), and zinc oxide with copper (Cu–ZnO; >99%) were acquired from Glentham Chemicals, Corsham, UK, whereas the conductive FTO glass was obtained from Pilkington, Minato-ku Tokyo Japan. The H2PtCl6.6H2O and 2-propanol were purchased from Sigma Aldrich, St. Louis, MO, USA.

2.2. Methods

In the present work, the structural investigations of the as-prepared undoped ZnO, Al-doped ZnO, and Cu-doped ZnO nanostructured films were performed using X-ray diffraction (XRD, diffractometer) with Cu Kα having a wavelength of 1.5406 Å. The X-ray photoelectron spectroscopic (XPS) investigations were carried out to study the chemical state of Zn, O, Al, and Cu on the surface of ZnO thin films. The XPS instrument was fitted with an Al Kα X-ray source maneuvering a 500 nm Rowland circle single crystal silicon (Si) monochromator emitting monochromatic light with at 1486.6 eV and a spread of ~0.85 eV. To record XPS spectral features of all the samples, the C 1s spectrum at 285.0 eV was taken as the reference. Both XRD and XPS investigations were performed in the center of the samples with an area of 20 × 10 mm2. The surface morphological features of the obtained films were probed with a scanning electron microscope (SEM). For the morphological characterization, the ZnO, Al–ZnO, and Cu–ZnO thin films were directly deposited onto a conductive FTO substrate. Furthermore, the optical characteristics in the UV–Vis region were examined from the absorbance spectra recorded on a spectrophotometer. The electrical properties including the resistivity, carrier concentration, and Hall mobility of all the samples were analyzed at room temperature by performing Hall effect measurements on a four-point probe. A fixed magnetic field was maintained throughout the Hall effect characterization.

2.3. Solar Cell Fabrication and Characterization

Solar cells were finally fabricated using the as-prepared undoped, Al-doped, and Cu-doped ZnO thin films as photoanodes. To prepare the counter electrode, Pt was deposited on an FTO substrate using a 5 mM solution of H2PtCl6.6H2O in 2-propanol and subsequent annealing at 450 °C. The Pt-coated FTOelectrode was situated onto the photoanode, and the edges of the cell were sealed mechanically through the silicone gasket and clamp. A hole was drilled in the counter electrode, through which the electrolyte was fed into the cell. After this, the hole was sealed with the help of tape. Finally, the photocurrent density–voltage (J–V) characteristics of the assembled solar cells were monitored both in the dark as well as illuminated conditions using a simulated solar radiation source with a constant flux of 700 mW/cm2 obtained through the Autosys DC3500 solar simulator, whereas the current and voltage characteristics were monitored through the Keithley 2400 source meter connected to a computer interface.

2.4. Fabrication of the ZnO, Cu–ZnO, and Al–ZnO Film

The undoped ZnO, Al–ZnO, and Cu–ZnO nanostructured films were deposited over the FTO substrate through a radiofrequency (RF) magnetron sputtering process with a base pressure of 4 × 10−4 Pa (Figure 1). To grow ZnO films, a high-purity ZnO (99.99%) sputtering target was used, while sintered mixtures of ZnO with Al2O3 (>99%) and ZnO with CuO (>99%) were used as targets for depositing Al–ZnO and Cu–ZnO films. Prior to film growth, all substrates were cleaned by ultrasonication in ethanol and acetone. Thereafter, film deposition was performed at constant sputtering power and Ar flow rate of 50 W and 70 sscm, respectively. The substrates were placed at a distance of 12 cm from the target. Prior to film deposition, a pre-sputtering step was introduced, with an RF power of 50 W for 10 min, to remove surface contamination. To maintain film uniformity, the substrates were continuously rotated at ~10 rpm during the film deposition duration.

3. Results and Discussion

Figure 2 depicts the X-ray diffraction (XRD) patterns of as-prepared undoped ZnO, Al-doped ZnO, and Cu-doped ZnO thin films. The strong diffraction peaks in the 2θ range of 36–36.5°, associated with the (101) plane, in all the samples, indicate the polycrystalline character of deposited films with a wurtzite structure. The absence of diffraction patterns of aluminum and copper oxides can be explained as follows: (a) the Al and Cu can either substitute for Zn2+ in ZnO lattice or enter the ZnO structure [27], (b) these species might be present in amounts lower than the detection limit of the characterizing tool, or (c) these species were segregated in the amorphous form at the grain boundaries [6].
To further confirm the successful injection of Al and Cu species inside the ZnO lattice as interstitial dopants, the oxidation states of Al and Cu in Al–ZnO and Cu–ZnO nanostructures were probed by recording X-ray photoelectron spectroscopy (XPS) spectra for all the samples, as shown in Figure 3. Figure 3a unveils a highly symmetrical Zn 2p core line, where the binding energies of Zn 2p3/2 and Zn 2p1/2 remained at 1021.80 ± 0.10 and 1043.80 ± 0.10 eV, respectively. These results confirm that in all the films, the largest majority of Zn atoms existed in the same formal valance state of Zn2+ inside the structure of ZnO. The absence of a peak at the binding energy of 1021.50 eV suggests that no metallic Zn was present, and only the oxidized state of Zn existed [28]. Figure 3b–d shows the O 1s, Cu 2p, and Al 2p spectra for the ZnO, Cu–ZnO, and Al–ZnO sample, which also support the presence of copper and aluminum in the ZnO lattices. The absence of any significant changes in the XPS spectrum of ZnO films after doping indicates that the Al and Cu atoms successfully substituted Zn2+ sites within the ZnO lattice.
The surface morphologies of the as-developed pure ZnO, Al–ZnO, and Cu–ZnO thin films were examined using scanning electron microscopic (SEM) studies, and the acquired images are shown in Figure 4. The figure evidently reveals uniform surface morphology without the presence of any surface defects, e.g., cracks and voids, mainly due to the low-temperature growth [29]. Furthermore, the SEM micrographs of both Al-doped and Cu-doped ZnO nanostructured films display little or no significant variations in the surface morphology vis-à-vis the undoped ZnO films, indicating the successful incorporation of Cu as a substitutional impurity. These results corroborated the findings of the XRD and XPS investigations. Nonetheless, the Al-doped ZnO films did show a slightly coarse natured surface, which can be attributed to the coalescence of the grain boundaries, as previously reported in the case of Al-doped ZnO films deposited via sputtering [12].
Moreover, the optical properties of the as-prepared doped and undoped ZnO-based nanostructures were investigated via UV–Vis spectroscopy. The resulting optical transmittance spectra for all the three samples, viz., pure ZnO, Al-doped ZnO, and Cu-doped ZnO films, are shown in Figure 5a. All samples exhibited an average transmission of more than 80% in the visible spectrum (400–800 nm). Further, doping with both Al and Cu caused a decrease in the transmittance of the ZnO nanostructure. Additionally, the red shift seen in the transmittance spectra of the doped samples can be ascribed to the generation of hole carriers due to doping, which shifted the Fermi level towards the valence band [27,30]. We have further estimated the bandgap energy for all three samples, from the Tauc expression:
(αhυ) = A (hυ − Eg)n
where A is a proportionality constant, υ denotes the incident radiation frequency, h denotes Planck’s constant, Eg is the optical bandgap of the material, and the exponent n represents the allowed transitions. By employing the above equation, it was possible to determine the optical bandgap of a material. Figure 5b plots (αhυ)2 as a function of hυ (photon energy) for ZnO, Al-doped ZnO, and Cu-doped ZnO films. The bandgap values were ascertained by extrapolating the straight linear portion of the (αhυ)2 versus (hυ) plot to intersect the x-axis. The estimated bandgap values for the as-deposited ZnO, Al–ZnO, and Cu–ZnO films were 3.3, 3.28, and 3.24 eV, respectively. It is noted that both Al- and Cu-doped ZnO thin films exhibited a reduction in bandgap in comparison to the pure ZnO film, which can be associated with an increase in the free carrier concentration as a result of doping [30].
Furthermore, Hall effect measurements were performed to analyze the electrical properties of the Al-doped and Cu-doped ZnO nanostructured films. Table 1 enlists the corresponding parameters of all the three films, such as mobility, carrier concentration, resistivity, and conductivity. It is clear from these data that the resistivity decreased following the introduction of both Al and Cu atoms into the ZnO lattice. The Cu-doped ZnO thin films demonstrated a minimum resistivity of 1.7 × 10−4 Ω cm, which was less than half of the resistivity of the undoped ZnO film (4.1 × 10−4 Ω cm), indicating the successful incorporation of Cu atoms as dopants [30,31]. This value of resistivity is comparable to or even lower than some of the previously reported works. For example, by using a low-vacuum heat-treated target, Ghanaatshoar et al. [29] reached a resistivity of 1.8 × 10−4 Ω cm in Al-doped ZnO thin films obtained using a sputtering process conducted at room temperature. Alternatively, the Cu-doped ZnO film revealed maximum conductivity (5.8 × 103 S cm−1), which was expected due to the highest carrier concentration in this sample. Interestingly, both carrier concentration and Hall mobility increased after doping in both Al- and Cu-doped films. The highest carrier mobility was expressed by the Cu-doped ZnO film, whereas the highest Hall mobility of 16.1 cm2 V−1 S−1 was observed for the Al-doped ZnO nanostructure, which was higher than most values previously reported in the literature [12,31]. It is well recognized that Hall mobility demonstrates strong dependence on crystallinity, texture, grain size, and variations in grain orientations [32]. The increase in carrier concentration after doping is attributable to the substitution of host cation sites by the dopant atoms and the subsequent release of the extra electrons [31]. The slightly lower carrier concentration in Al–ZnO films in comparison to the Cu-doped films can be associated with the clustering of Al atoms and the formation of stoichiometric Al2O3 [33,34]. These results confirm that the Al–ZnO and Cu–ZnO films prepared using the room-temperature sputtering technique have excellent electrical properties for use in solar cell applications.
Finally, the suitability of the prepared Al–ZnO, and Cu–ZnO thin films for use as electrodes in solar cells was assessed. The fabricated solar cells were exposed to a simulated light source, and the current-voltage characteristics, short circuit current density (JSC), an open circuit voltage (VOC) were recorded using a source meter. Figure 6 depicts the comparative photocurrent density–voltage (J–V) characteristics of different solar cells constructed from the pure ZnO, Al-doped ZnO, and Cu-doped ZnO nanostructures. The considerable changes in J–V characteristics of the doped films vis-à-vis the pure ZnO films suggest of the Al- and Cu-doped films have enhanced photoabsorption properties. The different device parameters as estimated from the J–V characteristics, viz., JSC, VOC, fill factor (FF), and power conversion efficiency (ƞ), are enumerated in Table 2. The ƞ and FF were determined using the following relations (29):
ƞ = (JSC VOC FF)/Pin
FF = (Jmax Vmax)/(JSC VOC)
where Pin denotes the incident light energy, and Jmax and Vmax are the current density and voltage, corresponding to the maximum output power in the J–V curves. From the table, it is evident that doping significantly improved the short circuit current densities of both Al-doped ZnO and Cu-doped ZnO nanostructures vis-à-vis the pristine ZnO films. Further, among the three types of photoanodes employed, the solar cells fabricated using Cu-doped ZnO exhibit a maximum photoconversion efficiency PCE of 0.56%, corresponding to short circuit current density (JSC) of 4.985 mA cm−2 and open-circuit voltage (VOC) of 0.315 V. Further, the Al-doped ZnO solar cell demonstrated an ƞ of 0.492% with a JSC of 1.539 mA cm−2 and a VOC of 0.547 V. In comparison, undoped ZnO offered merely 0.163%, 0.762 mA cm−2, and 0.533 V, respectively. Doping with either Al or Cu was found to improve the performance of ZnO-based solar cells.
The Cu-doped ZnO material showed considerably higher photoconversion efficiency, ~4 times higher than that of the undoped ZnO photoelectrode. Moreover, the Al-doped ZnO shows ~3 times higher photoconversion efficiency than pristine ZnO. The improved performance in the case of doped solar cells is ascribable to the dopant-created trapping levels close to the conduction band of ZnO nanostructure, favoring a rapid charge transfer rate and facilitating the forward movement of low energy electrons. Consequently, the doped structures have increased photon adsorption and effective change separation or reduced electron-hole pair (exciton) recombination, which in turn enhances the photoconversion efficiency [35].

4. Conclusions

In summary, we successfully prepared high-quality undoped ZnO, aluminum- and copper-doped ZnO thin films on FTO substrate via a facile room-temperature RF sputtering technique. The films revealed an average transmittance of ~80% in the visible region with low resistivity (2.9 × 10−4 Ω cm for Al–ZnO and 1.7 × 10−4 Ω cm for Cu–ZnO) and high carrier mobility (16.1 cm2 V−1 S−1 for Al–ZnO and 13.2 cm2 V−1 S−1 for Cu–ZnO). The low resistivity and high transmittance render these films suitable for application in transparent conductive electrodes of solar cells. Finally, the applicability of the prepared films was tested in solar cells. The Al-doped ZnO-based solar cells offered an efficiency of 0.492%, whereas the Cu-doped-ZnO-based solar cells exhibited the best performance with photocurrent of 4.985 mA cm−2 along with a power conversion efficiency of 0.56%, which were comparable vis-à-vis the values reported for solar cells. From these results, it can be clearly seen that the Cu–ZnO film shows the highest efficiency followed by the Al–ZnO thin film. We believe the investigations reported in this work will encourage further research activities in RF sputtered thin films for the fabrication of high-performance solar cells.

Author Contributions

M.W.A., M.Z.A., M.A. and S.A.A. did the experimental and characterization; M.W.-U.-R. and N.P. prepared the figures, data extraction revision. All the Authors contributed in writing the manuscript draft, editing and revision. All authors have read and agreed to the published version of the manuscript.

Funding

The authors acknowledge the Deanship of Scientific Research at King Faisal University for financial support under the DSR Annual Project (Grant No. 180102).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic presentation for the fabrication of the ZnO, Cu–ZnO, and Al–ZnO film.
Figure 1. Schematic presentation for the fabrication of the ZnO, Cu–ZnO, and Al–ZnO film.
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Figure 2. X-ray diffraction (XRD) patterns of as-prepared undoped ZnO, Al–ZnO, and Cu–ZnO thin film samples.
Figure 2. X-ray diffraction (XRD) patterns of as-prepared undoped ZnO, Al–ZnO, and Cu–ZnO thin film samples.
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Figure 3. (a) Zn 2p XPS spectra of ZnO, Al–ZnO, and Cu–ZnO; (b) O 1s spectra XPS spectra of ZnO, Al–ZnO, and Cu–ZnO; (c) Cu 2p XPS spectra of Cu–ZnO; and (d) Al 2p XPS spectra of Al–ZnO.
Figure 3. (a) Zn 2p XPS spectra of ZnO, Al–ZnO, and Cu–ZnO; (b) O 1s spectra XPS spectra of ZnO, Al–ZnO, and Cu–ZnO; (c) Cu 2p XPS spectra of Cu–ZnO; and (d) Al 2p XPS spectra of Al–ZnO.
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Figure 4. Scanning electron microscope micrographs of (a,b) as-deposited ZnO, (c,d) Cu-doped ZnO, and (e,f) Al-doped ZnO films at different magnifications.
Figure 4. Scanning electron microscope micrographs of (a,b) as-deposited ZnO, (c,d) Cu-doped ZnO, and (e,f) Al-doped ZnO films at different magnifications.
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Figure 5. (a) Transmittance spectra and (b) (αhυ)2 versus hυ (photon energy) plots, of pure ZnO, Al–ZnO, and Cu–ZnO.
Figure 5. (a) Transmittance spectra and (b) (αhυ)2 versus hυ (photon energy) plots, of pure ZnO, Al–ZnO, and Cu–ZnO.
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Figure 6. (a) Schematic diagram of prepared solar cell and (b) current density–voltage curve of the ZnO, Cu–ZnO, and Al–ZnO.
Figure 6. (a) Schematic diagram of prepared solar cell and (b) current density–voltage curve of the ZnO, Cu–ZnO, and Al–ZnO.
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Table
Table 1. Hall effect experimental parameters for the ZnO, Al–ZnO, and Cu–ZnO thin films.
Table 1. Hall effect experimental parameters for the ZnO, Al–ZnO, and Cu–ZnO thin films.
SampleHall Mobility (cm2 V−1 S−1)Carrier Concentration (cm−3)Resistivity (Ω cm)Conductivity (S cm−1)
ZnO11.32.7 × 10204.1 × 10−42.4 × 103
Al–ZnO16.13.5 × 10213.2 × 10−43.4 × 103
Cu–ZnO13.24.3 × 10212.04 × 10−45.8 × 103
Table
Table 2. The solar cell performance for ZnO, Cu–ZnO, and Al–ZnO.
Table 2. The solar cell performance for ZnO, Cu–ZnO, and Al–ZnO.
SampleVoc (V)Jsc (mA/cm2)PEC (%)
ZnO0.5330.7620.163
Al–ZnO0.5471.5390.492
Cu–ZnO0.3154.9850.559
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Alam, M.W.; Ansari, M.Z.; Aamir, M.; Waheed-Ur-Rehman, M.; Parveen, N.; Ansari, S.A. Preparation and Characterization of Cu and Al Doped ZnO Thin Films for Solar Cell Applications. Crystals 2022, 12, 128. https://doi.org/10.3390/cryst12020128

AMA Style

Alam MW, Ansari MZ, Aamir M, Waheed-Ur-Rehman M, Parveen N, Ansari SA. Preparation and Characterization of Cu and Al Doped ZnO Thin Films for Solar Cell Applications. Crystals. 2022; 12(2):128. https://doi.org/10.3390/cryst12020128

Chicago/Turabian Style

Alam, Mir Waqas, Mohd Zahid Ansari, Muhammad Aamir, Mir Waheed-Ur-Rehman, Nazish Parveen, and Sajid Ali Ansari. 2022. "Preparation and Characterization of Cu and Al Doped ZnO Thin Films for Solar Cell Applications" Crystals 12, no. 2: 128. https://doi.org/10.3390/cryst12020128

APA Style

Alam, M. W., Ansari, M. Z., Aamir, M., Waheed-Ur-Rehman, M., Parveen, N., & Ansari, S. A. (2022). Preparation and Characterization of Cu and Al Doped ZnO Thin Films for Solar Cell Applications. Crystals, 12(2), 128. https://doi.org/10.3390/cryst12020128

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