INVESTIGATION OF STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF MnO DOPED WITH Cu THIN FILMS PREPARED BY PLD TECHNIQUE FOR SOLAR CELL APPLICATIONS †

In the current study, concentrated Nd:YAG laser pulses at 500 mJ with a second radiation at 1064 nm (pulse width 9 ns) and repetition frequency (6 Hz) for 300 laser pulses incident on the target surface were employed to coat glass substrates with MnO thin films. Using an X-ray diffractometer (XRD), an atomic force microscope (AFM), and a UV-Vis spectrophotometer, the structural, morphological, and optical characteristics of the films doped with different concentrations of Cu content (0.03, 0.05, 0.07, and 0.09) were examined. The results show that the films are polycrystalline, with the largest peak appearing at an angle of 35.31, or a reflection of (111). The crystalline size of the deposited thin films was calculated using Debye Scherer formula and found to increase from 11.8 nm for undoped MnO 2 to 29.6 nm for doped (MnO) with the increase of Cu content from x=0 to x=0.09 at preferred orientation of (111). All the samples have a cubic structure. Also, the results showed that Cu content of the films affects the surface morphology. From the results of AFM analysis, it was found that the roughness and average diameter change when adding Cu to the structure, with the highest value occurring at Cu ratio 0.09 equal to 65.40 and 71.21 nm, respectively. UV–Vis spectrophotometer was used to investigate the optical transmission. It was found that when Cu content of films increased, the transmittance of films decreased. Hall Effect measurements show that all prepared films at RT have two type of conductivity P-type and n-type. The electrical characteristics of the (MnO) 1-x Cu x /Si heterojunction Solar Cell have been studied and found that the efficiency ( η ) decreases with the increase of Cu content.


INTRODUCTION
The use of thin film semiconductors has generated significant interest in a growing range of applications in various electrical and optoelectronic devices due to their low production costs, and thin film technology has a major position in basic research.An examination of the literature reveals that numerous research teams have studied thinfilm technology.As a result, a number of deposition processes have emerged, the majority of which depend on continuous, high-temperature power sources [1].Nanoparticles are the fundamental structures in nanotechnology, which has many applications in different areas such as biosensor and electronic nanodevices [2].An important class of nanostructured materials are the metal oxide thin films.It is possible to create the thin film's nanomaterials and grown using various methods.There are several widely used methods for depositing thin films onto a substrate, including pulsed laser deposition [3], chemical vapor deposition [4][5] reactive magnetron sputtering [6], spray pyrolysis [7], atomic layer deposition [8], chemical bath deposition [9] and so on.Manganese dioxide is one of the most attractive inorganic transition metal oxide materials from environmental and economic stand points.It is widely used in biosensors [10], catalysis [11], electrochromic multilayered nanocomposite thin films [12][13] and highperformance electrochemical electrodes and energy storage [14].Typically, MnO is a transparent semiconductor that is conducting with an n-type carrier [15].The pulsed laser deposition method involves ablating one or more targets that have been irradiated by a focused pulsed laser beam in order to produce thin films.This approach was originally used in 1965 by Smith and Turner [16].Due to its outstanding chemical stability, transparency, low toxicity, low cost, functional biocompatibility, excellent adsorption capacity, catalytic capabilities, and global availability, nanostructured manganese dioxide (MnO) is a potential transition metal oxide [17].The current study investigated the synthesis and characterization of optically transparent (MnO) films doped with different concentrations of Cu nanoparticles.The (MnO-Cu) thin films' structural, morphological, and optical characteristics were examined using UV-visible spectroscopy, atomic force microscopy, and X-ray diffraction (XRD).

EXPERIMENTAL 2.1 Preparation of Samples
Various concentrations of Cu nanoparticles (0.03, 0.05, 0.07, and 0.09 were used) were mixed with 99.99% pure MnO.In a gate mortar, the powder was mixed for five minutes.After that, it was compacted into pellets with a diameter of 1 cm and a thickness of 0.2 cm using a hydraulic press for 10 minutes at a pressure of 5 tons.After an hour of 400 °C sintering, the pellets were cooled to ambient temperature.

Deposition of Thin Films
The generated pellets were used to create thin films of (MnO)1-xCux on glass substrates with dimensions of 2.5×7.5 cm that had been cleaned employing an ultrasonic process and distilled water for 15 minutes.The pulsed laser deposition method was applied to produce thin films with the Nd:YAG laser.It produced 500 mJ of energy for 300 laser pulses that were incident on the target surface at a 45° angle and repeated at a frequency of 6 Hz.The deposition was done at (1-10-1) mbar of chamber pressure.The distance between the target and the substrate was 1.5 cm.The layer thickness of 200±5nm was estimated using the interference technique.

Measurements
By employing Cu-Ka (= 0.154 nm) throughout a 2-scan range of 10-80°, the structural properties of (MnO) 1-x Cu x thin films were studied by an X-ray diffractometer (Philips PW1730).Atomic force spectroscopy (AFM) was used to investigate the surface morphological characteristics of the film.Using a UV-Vis-NIR spectrophotometer with a 190-1100 nm wavelength range (Metertech SP8001), the optical characteristics of thin films were investigated.

RESULTS AND DISCUSSIONS 3.1 The X-rays Diffraction Results
Figure 1 displays the XRD patterns of different Cu concentrations in doped and undoped MnO thin films.The outcomes demonstrated the polycrystalline nature of the films.This outcome is consistent with Zahan et al. [18].By comparing the results with ASTM card files (No. 96-900-6666), the diffraction peaks are identified.MnO-Cu thin films were discovered to have a cubic structure.There are two strong peaks and three other smaller ones in the X-ray diffraction spectra of MnO.It denotes the polycrystalline nature of the film.The strongest peak in the XRD pattern was at an angle of 35.31, which corresponds to a reflection of (111).It was observed that two additional strongest peaks developed at an angle of 40.85, which corresponded to a reflection of (200), when Cu with (0.05 and 0.07) content was added to the films.This demonstrates the impact of copper content.The Debye-Scherer equation was used to determine the crystal's size (Cs) [19][20][21]  (1) Where: θ the diffraction angle,  full width at half maximum (FWHM), and λ wavelength of the X-ray are all given.
In accordance with the Debye-Scherer equation as well.For (111) and ( 200), the findings are shown in Table 1.Average crystallite size, interplanar spacing, and the number of planes in the diffraction pattern of undoped and doped MnO thin films with various Cu contents Table 1 results showed that the average crystallite size had increased along with the increase in copper concentration.In contrast to earlier research, this study's findings revealed [18].

Atomic force microscopic
Analysis of the surface morphology of films grown on glass substrates can be done by using 3D AFM images of MnO thin films doped with various concentrations of Cu nanoparticles to calculate the mean diameter, mean roughness, and mean square root (RMS).The fine morphology and roughness of the MnO films may be seen with various Cu activators.Roughness and RMS change increased with the addition of Cu, with a Cu ratio of 0.09 producing the maximum value.The 0.09 Cu ratio is the best among the other ratios, based on the findings of the XRD and AFM tests (it produced the highest roughness and largest crystalline size).Table 2. Granular content and total surface roughness of the produced films at room temperature

The optical properties
Undoped and doped (MnO) thin films with varying concentrations of Cu (0.03, 0.05, 0.07, and 0.09% wt.) were studied for transmission, absorption coefficient, extinction coefficient, refractive index, dielectric constant, and optical energy gap in the wavelength range of 500-1100 nm.For (MnO-Cu) produced at RT, Figure 3 depicts the transmission variation with wavelength.The image and Table 3 make it clear that the transmittance value is inversely proportional to the Cu concentration; as the Cu content in MnO films increased, so did the transmittance value.
The relation [22,23] can be used to get the absorption coefficient: where t is the sample's thickness and A is the absorbance.The following relation [24] can be used to compute the optical energy gap's value: ( ) where B is a constant inversely proportional to the degree of amorphousness, hv is the energy of the input photon, r is the exponent denoting the kind of optical transitions in the material, and Eg is the optical bandgap.Figure 5 shows that optical bandgap measurements fall from roughly 2.69 eV to 2.19 eV at room temperature when the Cu content increases from 0% to 9%.
Figure 6 shows the connection between the extinction coefficient (k) and wavelength in the 500-1100 nm range for samples made at room temperature, illustrating how the k values climb as the doping level increases.Table 3 provides an illustration of the results.The values of k were calculated based on the relationship shown in [25].3 Show how the refractive index changes with wavelength for undoped and doped MnO with different amounts of Cu in the wavelength range of 500-1100 nm.It can be seen that the refractive index rises as the doping increases.The complicated optical refractive index of thin films is described by equation ( 5) [26]: where (n) and (k) are the real portion and imaginary part of a complex refractive index, respectively, and (n*) is the complex refractive index.While the relationship [27] can be used to determine the simple refractive index: ( ) Figures 8 and 9 show the real and imaginary portions of the dielectric constant of undoped and doped (MnO) thin films with different Cu concentrations (0.03, 0.05, 0.07, and 0.09), respectively, in the wavelength range (500-1100 nm) at room temperature.Since (k2) is much smaller than (n2), part (per Equation 7) simply depends on the value of (n2).The imaginary portion, however, is dependent on the value of (k) (see Equation 8).It was discovered that their values increased as the doping and wavelength were raised, as indicated in Table 3. Applying the equations [28], the real and imaginary components of the dielectric constant were computed.

Hall Effect
Undoped and doped (MnO) thin films with varying Cu contents (0.03, 0.05, 0.07, and 0.09) wt were studied using Hall Effect measurements.Table (4) shows that all samples exhibit a positive negative Hall coefficient (i.e., n-type conductivity), with the exception of films doped at x = 0.05, 0.07, where the Hall coefficient sign has been transformed to p-type due to the high concentration of carriers.Additionally, the results demonstrate that a drop in the values of charge carriers (n) with a decrease in both the mobility (μ H ) and Hall coefficient (R H ) values causes an increase in the value of electrical conductivity (σ).

Current-Voltage Characteristics Measurements at Illumination
Show the J-V characteristics of the (MnO) 1-x Cu x /Si heterojunction made by pulsed laser deposition at different Cu concentrations (x = 0.03, 0.05, 0.07, and 0.09) under ambient lighting (100 mW/cm2) at room temperature.The values of J-V parameters (Voc , Isc , Vm , Im , F.F and η) were tabulated in Table 5 .In general, it can be observed that the Isc decreases as the cu content increases.It is noticed a decrease in the values of the fill factor and the efficiency value as the Cu content increases and further result in a poor electrocatalytic performance this outcome is consistent with Peng et al. [29].

CONCLUSION
The impact of doping (MnO) thin films with various Cu contents on their structural, morphological, and optical features was investigated in the current work.The films' polycrystalline nature was demonstrated by the XRD pattern, which had the highest peak present at an angle of 35.31, which corresponded to a reflection of (111).The ratio of 0.09 percent Cu is the best among the other ratios, according to the XRD and AFM analyses (it produced the highest crystalline size and the highest roughness).The absorbance coefficient rose for all samples as the doping ratio rose.It was discovered that as the doping ratio grew, the refractive index, extinction coefficient, and dielectric constant (real and imaginary parts) all increased.Hall Effect measurement showed that films have n-type to all samples except (0.03 and 0.05) in RT.J-V characteristic showed the maximum efficiency which was 0.21% at MnO-Cu (0.03) at RT and the value of the filling factor decreases with doped Cu at (RT).

Figure 1 .
Figure 1.Shows the X-ray diffraction of Cu nanoparticles doped in different quantities in MnO .

Figure 2 .
Figure 2. Shows 3D AFM images of room-temperature-produced MnO thin films doped with different amounts of Cu nanoparticles

Figure 3 .Figure 4 .
Figure 3. Shows the transmittance spectra of Cu nanoparticledoped MnO thin films at various concentrations Figure 4. Shows the absorption coefficient of thin films of MnO doped with various concentrations of Cu nanoparticlesBand-to-band absorption causes a significant increase in an electron's absorption when it is moved up to the conduction band from the valence band, producing a new pair of charge carriers (an electron and a hole).The bandgap values for the various Cu contents are shown in Table3.The absorbance increases as Cu concentration (x) increases and Eg decreases.

Figure 5 .Figure 6 .Figure 7
Figure 5. Shows the plot of (αhυ) 2 as a function of (hυ) for thin films of MnO doped with various concentrations of Cu nanoparticles Figure 6.Shows the MnO thin films doped with various concentrations of Cu nanoparticles and their extinction coefficients (k)

Figure 7 .
Figure 7. Shows the refractive index of thin films of MnO doped with various concentrations of Cu nanoparticles.

Figure 8 .Figure 9 .
Figure 8. Shows the real component of the dielectric constant films of MnO doped with various of Cu nanoparticles Figure 9. Shows the imaginary portion of the dielectric constant for thin films of MnO doped with various concentrations of Cu nanoparticles Doaa T.Mohammed, et al.

Figure 10 .
Figure 10.J-V characteristics under illumination by 100mW/cm 2 white light for MnO/p-Si at R.T.

Table 1 .
Lists the crystal size, FWHM, and interplaner distance for (MnO) thin films doped with various concentrations of Cu nanoparticles.

Table 3 .
Shows the transmittance, absorption coefficient, and optical constant of (MnO) thin films at room temperature that are both undoped and doped with (Cu) in the following ratios: 0.030.050.070.009.

Table 4 .
Hall coefficient, Hall mobility, carrier concentration, and conductivity type for MnO films doped with various Cu at RT

Table 5 .
Photovoltaic characterization (Voc, Isc, Vm, and Im) of (MnO)1-xCux/p and n-Si heterojunctions illuminated by 100mW/cm 2 white light with different Cu content prepared at RT