RETRACTED: The Effect of 600 keV Ag Ion Irradiation on the Structural, Optical, and Photovoltaic Properties of MAPbBr₃ Films for Perovksite Solar Cell Applications

Abstract

A competitive new technology, organic metallic halide perovskite solar cells feature a wide working area, low manufacturing costs, a long lifespan, and a significant amount of large efficacy of power conversion (PCE). The spin-coating technique was utilized for the fabrication of pure CH₃NH₃PbBr₃ (MAPbBr₃) thin films, and these films are implanted with 600 keV silver (Ag) ions at fluency rate of 6 × 10¹⁴ and 4 × 10¹⁴ ions/cm². XRD analysis confirmed the cubic structure of MAPbBr₃. A high grain size was observed at the fluency rate of 4 × 10¹⁴ ions/cm². The UV-Vis spectroscopic technique was used to calculate the optical properties such as the bandgap energy (E_g), refractive index (n), extinction coefficients (k), and dielectric constant. A direct E_g of 2.44 eV was measured for the pristine film sample, whereas 2.32 and 2.36 eV were measured for Ag ion-implanted films with a 4 × 10¹⁴ and 6 × 10¹⁴ ions/cm² fluence rate, respectively. The solar cells of these films were fabricated. The J_sc was 6.69 mA/cm², FF was 0.80, V_oc was 1.1 V, and the efficiency was 5.87% for the pristine MAPbBr₃-based cell. All of these parameters were improved by Ag ion implantation. The maximum values were observed at a fluency rate of 4 × 10¹⁴ ions/cm², where the V_oc was 1.13 V, FF was 0.75, J_sc was 8.18 mA/cm², and the efficiency was 7.01%.

1. Introduction

In a very short amount of time, perovskites solar cells (PSCs) have attracted the attention of the photovoltaic industry by providing a solar-to-electric power conversion efficiency (PCE) rate greater than 23%. Currently, it is a potential candidate among commercially available solar cells, and nanomaterials play the main role in their efficiency [1,2,3,4,5,6]. Inorganic–organic hybrid perovskites of metals halides have a general formula: ABX₃, where the A-site is composed of organic cations that usually consist of MA⁺ (CH₃NH₃⁺), Cs⁺, and FA⁺ [(NH₂)₂CH]⁺ ions, etc.; the B-site is composed of metallic cations, generally Pb²⁺, as other ions, such as Ge²⁺ and Sn²⁺, can easily oxidize to +4 states; the X-sites are composed of halide ions, e.g., Cl⁻, Br⁻, or I⁻ [7,8]. The common inorganic–organic perovskites compounds are FAPbI₃ and MAPbI₃. The MAPbI₃-based PSCs have many benefits, like high charge extraction rate, and they can absorb a large range of visible light [9]. However, as it becomes crude in humid conditions, it cannot be commercialized on a large scale [10]. Thus, as an alternative to MAPbI₃, MAPbBr₃ is a promising candidate with a large bandgap of 2.2 eV that provides a high open-circuit voltage (≈1.2−1.5 V) [11,12]. Its excitonic length of diffusion is greater than 1.2 μm, which enables it with good charge transport ability within a device [13]. In addition, MAPbBr₃, in comparison to pseudo-cubic MAPbI₃, has a stable cubic phase that provides good stability in air or moisture conditions and low ionic mobility [14,15]. These favorable features of MAPbBr₃ provide a large binding energy (76 MeV), high light absorption beyond the limit of 550 nm, and high efficiency [15,16].

Various studies have revealed that there are several fundamental properties on which the efficiency of perovskite solar cells (PSCs) depend. These properties include a high coefficient of absorption, a long lifetime of photogenerated species, and the tuneability of the band gap by changing the halide (i.e., bromide and iodide) fabrication of the perovskite precursor solution [17,18,19]. Due to the fact of these favorable features, ABX₃-type hybrid perovskite compounds are capable of developing solar cells with PCE greater than 22%. However, some problematic issues still exist in PSCs such as instability in moisture and intensive light illumination as well as the presence of harmful Pb²⁺ ions. These serious issues provide the upper limit to their commercial development and higher efficiency [20,21]. Many approaches, such as substitutional changing of the A-site and X-sites with inorganic ions, have been utilized thus far, but remarkable results have not been achieved. To improve the stability, PSCs are optionally encapsulated by organic or inorganic materials [22] for the better dispersion of the microspheres of porous Si deposited on the surface of PSCs [23]; in addition, hydrophobic materials are also deposited to increase the stability and reduce the number of recombination centers [24]. Although these approaches are affected but cannot improve the stability of PSCs, another approach that is considered useful for improving the efficiency, thermal stability, and phase maturity of ABX₃-type perovskites is the partial substitution of Pb⁺² ions from B-sites with metallic ions [25,26,27].

This substitution of Pb²⁺ cations is an important and promising methods for increasing perovskite stability. Thus, replacing a toxic Pb⁺² with a nontoxic element to improve the stability is a common task for scientists [28]. There is a wide range of cations with different atomic radii that may induce suitable changes in perovskites. However, as the formation of cations from the B-site requires a higher formation energy in comparison to A-sites and X-sites, they are more difficult to develop [24,29]. Thus, B-site doping is still a very sensitive issue [28,29]. Doping via a chemical method is a good technique for adding metal ions to a B-site, but this method is not effective, because chemical impurities can be added to the ABX₃ structure, which reduces the efficiency and stability of the cell. Ion implantation is a good technique, compared to the chemical method, for the doping of metal ions in B-sites of perovskites. This involves the bombardment of the substrate with ions, accelerating to higher velocities. It requires a low-temperature process with no damage and selecting the quantity fabricated is also possible. It allows for controlling the precise dose and depth. These capabilities are not possible with doping [30,31]. In ion implantation, there are several controlling factors that make it versatile, e.g., the dopant fluency, dopant energy, and depth. Therefore, ion implantation can substitute metallic ions in the B-site of perovskite. Different metallic ions can be doped in the MAPbBr3 structure, but Ag is the most suitable for adding to B-sites due to the fact of its nontoxicity, abundance, cubic structure, and high stability. Ag has an atomic radius of 1.72 Å, which is comparable to the atomic radius of Pb, which is 1.8 Å [32]. Therefore, it will not change the structure of ABX₃. During ion implantation, when Ag ions replace Pb ions in the B-site, it increases the electrical properties and stability of solar cells [33,34].

In this study, Ag ions were inserted in place of Pb via the ion implantation technique, which is a good doping technique compared to other chemical techniques. The Ag ions increased the stability and performance of the device. The detailed structural and optical properties of the Ag-implanted MAPbBr₃ films are discussed, which have not previously been explored in other studies. It was observed that the Ag ions did not disturb the stable cubic phase of MAPbBr₃. This indicated that the cells fabricated with Ag ions would be stable and have a long lifetime. Here, Ag ions affected the photovoltaic characteristics were investigated, and it was observed that the PSC fabricated at 4 × 10¹⁴ ions/cm² had a high photovoltaic performance. From the literature survey, it was found that Ag ion implantation in MAPbI₃ needed to be addressed.

2. Experimental Section

The precursors of MAPbBr₃ perovskite, such as bromides of MA and Pb, were purchased from Sigma-Aldrich, UK. To prepare the 1 M solution of MAPbBr₃ perovskite, dimethyl-sulfoxide and n-dimethyl-formamide were mixed together at a volumetric ratio of 7:3 and left for 12 h. Solution of Perovskite was coated onto FTO glass substrates using the spin-coating technique for 10 seconds at a speed of 4000 rpm. The FTO was bathed with deionized (DI) water first, then with isopropanol and ethanol before deposition. At fluence rates of 4 × 10¹⁴ and 6 × 10¹⁴ ions/cm², two films received 600 keV Ag irradiation. After Ag ion implantation, the films were annealed in a furnace for 10 min at 100 °C.

The structural properties of the films were studied by X-ray diffractogram (D/MAX-2400), Vianna, Austria. UV-Vis spectroscopy (U-4100) was used to measure the optical characteristics, China.

The solar cells of these films were fabricated on TiO₂/FTO/glass substrates. TiO₂ film was coated onto the FTO/glass substates using a previously published technique [35]. For the preparation of hole transport material (HTM), 36 mL of TBP and 22 mL of a stock solution of 520 mg/mL lithium bis-trifluoromethyl sulfonyl-imide were combined to create solution (A). In solution (A), 72 mg of spiro-OMeTAD was added and stirred, and a solution formed called solution (B). Chlorobenzene (1 mL) was dissolved in solution (B) to prepare a final solution. The volatilized gold layer, with an 80 nm thickness, was coated on the top of the electrode. The gold coating increased the wettability of the photo-active layer, increased the performance time, and established a better contact of device with the external source [36]. The cell’s active area measured 0.16 cm².

The efficacy of cells was recorded by a solar simulator (AM 1.5G illumination at 100 mWcm⁻² using a source meter from Keithley 2450). The stepwise deposition of different layers is shown in Figure 1.

3. Results and Discussion

3.1. XRD Analysis

An XRD graph of the pristine and Ag-implanted MAPbBr₃ films is shown in Figure 2. In the pristine MAPbBr₃, four peaks appeared at 2θ values of 14.66°, 29.16°, 42.20°, and 45.54°, having a plane orientation (100), (111), (222), and (320), respectively. All peaks confirmed the cubic perovskite structure of MAPbBr₃, which has also been reported in the literature [37]. For the Ag-implanted MAPbBr₃ at the fluency rate of $4\times {10}^{14}$ ions/cm², the four peaks were observed at 2θ values of 14.59° (100), 28.77° (111), 42.16° (222), and 45.48° (320). Here, the peaks shifted, and the intensity of the peaks increased, which indicates that the crystallinity of the film increased. At the fluency rate of $6\times {10}^{14}$ Ag ions/cm², the four peaks were located at 2θ values of 14.50° (100), 28.72° (111), 42.20° (222), and 45.44° (320). All peaks were shifted toward lower 2θ angles, and no additional peaks related to AgBr, AgPb, etc., were observed, which attests to the stability of the phase and the correct replacement of Ag ions in the MAPbBr3 host [38]. Additionally, it indicated the absence of stresses in the unit cell [39].

3.1.1. Grain Size (D) and Dislocation Line Density ($\delta$)

$\delta$ and D of highly intense (100) peaks were measured using the following formulas [40,41]:

$$D=\frac{0.9\lambda }{\beta \cos \theta }$$

(1)

$$\delta =\frac{1}{D^2}$$

(2)

Here, λ is the wavelength; β and θ are the FWHM and Brag’s angle, respectively [42].

For pure MAPbBr₃ films, D was 19 nm and $\delta$ was $3.52\times {10}^{15} {\mathrm{m}}^{-2}$ as shown in Figure 3. For the Ag-implanted MAPbBr₃, D and $\delta$ at the fluency rate of $4\times {10}^{14}$ ions/cm² were 26 nm and $3.44\times {10}^{15} {\mathrm{m}}^{-2}$, respectively. The high value of the grain size refers to the proper substitution of Ag ions in the ABX₃ structure due to the fact that the crystallinity of the film was high, as a high peak intensity was observed at this fluency rate in the film. The low value of $\delta$ indicated that the scattering of electrons was low due to the small grain boundaries. At a rate of $6\times {10}^{14}$ ions/cm², D and $\delta$ were 22 nm and $4.42\times {10}^{15} {\mathrm{m}}^{-2}$, respectively. The high value of Ag ions indicates that they did not occupy the vacant Pb sites, as they remained on the surface of MAPbBr₃ due to the fact of small vacant sites. Therefore, D was reduced because of bonding between Ag ions and the inner atoms of MAPbBr₃ [43]. These results match the previously published literature, where D decreased with a high amount of doping of divalent/trivalent ions in a MAPbBr₃ structure [44,45]. The high concentration of Ag ions forms a network with MAPbBr₃, which will increase and decrease the recombination rate [46].

3.1.2. d-Spacing

Figure 4 shows the d-spacing of the pure and Ag ion-implanted MAPbBr₃ films. The d-spacing was measured by Bragg’s Law [5,30].

$$d=\frac{n\lambda }{2\sin \theta }$$

(3)

where n is order of diffraction.

The values of d-spacing for the (100) peak of the pristine and the $4\times {10}^{14}$ ions/cm² and $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ films were 6.11 Å, 6.1 Å, and 6.04 Å, respectively. The measured values showed a cubic crystal behavior according to file number PDF#21–1272 [5,30]. A slight decrease in the d-spacing values was observed by ion implantation. The decrease in d-spacing was due to the fact that Ag has a smaller ionic size. The slightly low value of the d-spacing shows that strong bonding was present between atoms and atoms and between planes and planes in the film’s structure [31]. This will benefit the enhancement of the stability of the structure.

3.1.3. Lattice Parameters and Volume

The lattice parameters and volume of a unit cell of pure and Ag-irradiated MAPbBr₃ were calculated using Equations (5) and (6) and are shown in Figure 5.

a = d_hkl(h² + k² + l²)^1/2

(4)

V = a³

(5)

Here, hkl is the Miller indices of the most intense peak (i.e., (100)); V and a are the volume and lattice parameters of the unit cell.

The a and V of pure and $4\times {10}^{14}$ ions/cm² and $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ films were $6.11\times {10}^{-10}$ and $2.28\times {10}^{-28} {\mathrm{m}}^3$, $6.10\times {10}^{-10}$ and $2.20\times {10}^{-28} {\mathrm{m}}^3$, and $6.04\times {10}^{-10}$ and $2.27\times {10}^{-28} {\mathrm{m}}^3$, respectively. A decreasing trend in a and V was observed as shown in Figure 5 and

Table 1. The D, δ, a, and V of pure and Ag-implanted MAPbBr₃ films.

Sample	D (nm)	$\mathit{\delta }$$(\times {10}^{15}){\mathbf{m}}^{-2}$	a (Å)	$\mathbf{V} (\times {10}^{-28}){\mathbf{m}}^3$
PureMAPbBr3	19	3.52	6.11	2.28
$\mathrm{Ag}-{\mathrm{MAPbBr}}_3 (4\times {10}^{14}$ m2)	26	3.44	6.10	2.20
$\mathrm{Ag}-{\mathrm{MAPbBr}}_3 (6\times {10}^{14} {\mathrm{m}}^2)$	22	4.42	6.04	2.27

. As Ag has a smaller radius than Pb, the volume of the unit cell therefore decreased. This was also confirmed from the XRD graph, where the peaks were shifted toward a small angle. Due to the fact of this decrease in volume, atoms become too close to each other, and the binding energy and number of electrons per unit volume increase. These large electrons will increase the electrical properties of the film, resulting in the improvement of the efficiency of the films.

3.2. Optical Properties

For solar cells, a material’s optical characteristics are crucial. This section explains optical parameters including refractive index, band gap energy, optical dielectrical constants, and extinction coefficient.

3.2.1. Energy Band Gap

The response of the material under the irradiation of light highly relies on its band gap and the energy of the incident photon. The photons energize the electrons with energy (hν) more than bandgap energy (E_g) upon impact with the material; then, they absorb this energy due to the interband transition of the electrons. This phenomenon helps in analyzing the absorption edges of the material. To determine the bandgap of the material, these absorption edges were used with Tauc’s formula [47,48].

$${(\alpha h\upsilon )}^2=B\left(h\upsilon -E_g\right)$$

(6)

Here, α is coefficient of absorption; B is a constant; hν is the energy of the incident photon; E_g is the bandgap of the material [49]. The value of E_g was measured from Figure 6 by extrapolating it at zero-ordinate. The E_g of pure MAPbBr₃ was calculated as 2.44 eV. When Ag was irradiated onto MAPbBr₃ film at rate of 4 × 10¹⁴ ions/cm², its E_g decreased to 2.32 eV. The exchange interaction of sp-d between the localized “d” electrons of the transitions metals ions at the cation site and band electrons was used to explain this decrease in E_g [50]. The 5s and p orbitals of Ag and halogen respectively are contributed to the valence band’s upper edge, and only the 5p orbital of Ag do so for the conduction band’s lower edge. The level of energy of the 6p empty orbitals of Pb²⁺ is lower than the 5p empty orbitals of Ag²⁺ when the affinity of electrons and redox potential of Pb²⁺ are taking into account [51]. As a result, the conduction band’s bottom shifts downward with rising Ag content. This decrease in E_g is because of an increase in the ‘D’ of the film [52]. At a fluency rate 6 × 10¹⁴ ions/cm², E_g was increased to 2.36 eV. This increase in E_g was due to the decrease in the grain size of the film. An E_g of 2.32 eV is most suitable for harvesting energy in the visible range [53]. The same results were also reported by Albert et al., where they doped the polycrystalline MAPbBr₃ film with N₂ and observed a low recombination rate [54].

3.2.2. Extinction Coefficient (k) and Refractive Index (n)

The n is a very important factor in photo-electronic and solar cell devices, because it analyzes the opto-electrical characteristics of the material. The refractive index can be measured by Lorentz classical theory [45,55].

$$n=\sqrt{1+{\left(\frac{A}{E_g+B}\right)}^2}$$

(7)

Here, the constants are B and A having values are 3.4 eV and 13.6 eV, respectively. The measured refractive indexes for pure and $4\times {10}^{14}$ and $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ were 2.46, 2.60, and 2.56, respectively. The film implanted with at $4\times {10}^{14}$ ions/cm² had a high refractive index, which is suggested good for the appications of solar cell. The high value of n increases the polarizability of the film [56,57]. Due to the high value of n, more light will scatter, leading to more energetic electrons being emitted. These high numbers of electrons will increase the current density of solar cells, which will cause the efficiency of the cell to increase.

The extinction coefficient k is calculated by [58]:

$$k=\frac{n}{\mathsf{\Delta }{\chi }^{\ast \gamma }}$$

(8)

Here, γ = −0.32 is the constant, and “∆χ∗” is the electronegativity [59]. The measured k for pure and $4\times {10}^{14}$ and $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ were 2.16, 2.23, and 2.21, respectively, as shown in Figure 7. When Ag ions were implanted, k increased, as it has a direct relation with n. The high value of k was observed at a fluency rate of 4 × 10¹⁴ ions/cm⁻².

3.2.3. Dielectric Constants (ε_r, ε_i)

The optical constants of dielectric are related to a material’s inherent qualities. The dielectric constants are made up of real and imaginary elements. The real components refer to the light’s speed in the materials. The imaginary component concerns the dielectric material, which, as a result of dipole motion, absorbs energy from an electric field. The ratio between ε_r and ε_i determines the loss factor [60]. Additionally connected to dielectric constants are k and n. The relationship between polarizability and dielectric constant for every solid substance is proportional. The optical bandgap and position density are connected. Therefore, It is crucial to determine the dielectric constants precisely [61].

ε = ε_r + i ε_i

(9)

The ε_r and ε_i are determined using the given relations [62]:

ε_r = n² − k²

(10)

ε_i = 2nk

(11)

Photon energy is necessary for both ε_r and ε_i. The ε_r of the pure and $4\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ films had higher values, and the value for the $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ film decreased. The ε_i allows for a comparison between the same refractive index values, as is shown in

Table 2. ε_r and ε_i of undoped MAPbBr₃ and Ag ion-implanted MAPbBr₃ films.

Sample	Real Dielectric Constant	Imaginary Dielectric Constant
	εr	εi
MAPbBr3	1.43	10.58
4 × 1014 Ag ion MAPbBr3	1.79	11.60
6 × 1014 Ag ion MAPbBr3	1.67	11.32

. ε_r and ε_i are at the maximum at a $4\times {10}^{14}$ ions/cm² Ag ion concentration.

3.3. J-V Measurement

The conduction band (CB) and valence band (VB) edges for the construction of PSCs are very important. The CB edge of the perovskite film should be greater than the CB of the electron transport layer, and the VB edge of perovskite film should be greater than the VB of the hole-transport layer. The method for calculating the CB and VB edges of MAPbBr₃ film is explained below [63]. The formula for MAPbBr₃ is CH₃NH₃PbBr₃, which includes one carbon, six hydrogen, one nitrogen, one lead, and three bromide atoms.

Electron affinity for C = E_EA = 1.26/96.48 = 1.26 eV;

First ionization energy for C = E_ion = 1086.5/96.48 = 11.26 eV;

Average energy = X_C = 1/2(E_EA + E_ion) = 1/2(1.26 + 11.26) = 6.26 eV.

Similarly, the average energies of H, N, Pb, and Br were calculated, which were 6.42, 7.27, 3.52, and 4.24 eV, respectively.

Now:

X_CH3NH3PbBr3 = [6.26 × (6.42)⁶ × 7.27 × 3.52 × (4.24)³]^1/12;

X_CH3NH3PbBr3 = 2.56 eV;

E_c = 2.56 − 4.5 − Eg/2 = −3.2 eV;

Ev = Ec − Eg = −5.60 eV.

These values matched well with the available literature [64].

Figure 8 shows the energy band structure diagram of a Ag/Spiro-OMeTAD/MAPbBr₃/TiO₂/FTO/glass solar cell. Light at a suitable frequency falls on the MAPbBr₃, and then electron–hole pairs are generated. The electron accelerates toward the CB of TiO₂, which is close to the CB of MAPbBr₃, and the hole moves toward the VB of spiro-OMeTAD, the VB level of which is just above the VB level of MAPbBr₃. In this way, the electron moves towards the circuit causing the current to flow through the solar cell.

Figure 9 shows the J-V curve of pure and Ag-irradiated MAPbBr₃ solar cells. These curves were used to calculate the photovoltaic parameters of the pure and Ag-irradiated MAPbBr₃-based solar cells such as the short circuit current density (J_sc), conversion efficiency (η), open-circuit voltage (V_oc), and fill factor (FF), as summarized in

Table 3. Solar cell parameters of MAPbBr₃ and Ag-irradiated MAPbBr₃.

Sample	Jsc	Voc	FF	Efficiency (η)
MAPbBr3	6.69	1.1	0.798	5.87
$4\times {10}^{14}$ Ag-irradiated MAPbBr3	8.18	1.13	0.759	7.01
$6\times {10}^{14}$ Ag-irradiated MAPbBr3	7.08	1.11	0.790	6.21

. To determine the power conversion efficiency, the Equation (12) was used [65].

$$\eta =\frac{FF\times V_{OC}\times J_{SC}}{P_{in}}$$

(12)

Here, P_in stands for the input power of the incident light. The FF is computed as follows [66]:

$$FF=\frac{I_{\max }\times V_{\max }}{J_{SC}\times V_{OC}}$$

(13)

Here, I_max and V_max are the maximum current and maximum voltage, respectively.

For the pure MAPbBr₃-based solar cells, the calculated J_sc, V_oc, FF, and efficiency were measured as 6.69 mAcm⁻², 1.1 V, 0.79, and 5.86%, respectively.

When silver (Ag) ions were irradiated on the film of a sample MAPbBr₃ at a fluency rate of $4\times {10}^{14}$, the photovoltaic parameters (i.e., J_sc, V_oc, and FF) improved and the efficiency increased from 5.86 to 7.01%. The improvement in photovoltaic parameters was caused by the irradiation of Ag ions, because they not only facilitate the growth of grains but also reduce the size of grain boundaries [48,67]. The grain boundary resistance is decreased by enhancing the charge carriers, which improves the J_sc [68,69]. In addition, Ag is a noble metal, and it increased the number of free electrons in the MAPbBr₃ films, causing Jsc and FF to increase [70]. A high FF means that the recombination rate was reduced; therefore, the efficiency of the solar cell increases. Ag has free electrons, and a small amount of energy will cause the loss of these electrons from Ag and improve the concentration of free electrons in MAPbBr₃; therefore, the J_sc is improved [71].

Additionally, it is observed from Figure 8 that the CB edge of MAPbBr₃ came close to the CB of TiO₂ by Ag ion implantation. Therefore, the electrons easily transferred from the CB of MAPbBr₃ to the CB of TiO₂; hence, J_sc increased leading to the increase the cell’s efficacy.

At a high flounce rate of 6 × 10¹⁴ ions/cm², the efficiency of the cell decreased from 7.01% to 6.21% by decreasing J_sc and FF. The high value of Ag ions could not fit in the structure of MAPbBr₃ as explained by XRD. The grain size decreased leading to the increase in the resistivity. Therefore, the recombination rate increased, which reduced the injection efficiency of the electrons from the CB of MAPbBr₃ to the CB of TiO₂; hence, J_sc was reduced and, finally, the efficiency was reduced, which has promising applications for harvesting solar light [72,73].

4. Conclusions

Perovskite solar cells of pure and $4\times {10}^{14}$ and $6\times {10}^{14}$ ions/cm² Ag ion-implanted MAPbBr₃ films were successfully prepared. All films had a stable cubic phase, and the film implanted with $4\times {10}^{14}$ ions/cm² Ag ions had a large grain size, low bandgap (E_g), and high refractive index (n) according to XRD and UV-Vis analyses. These properties make it a good material for the fabrication of solar cells. Solar cells using these films were prepared. All solar cells showed good efficiency, but the cells formed with $4\times {10}^{14}$ ions/cm² Ag ions implanted in the MAPbBr₃ film showed high V_oc (1.13 V), J_sc (8.18 mA-cm⁻²), FF (0.75), and efficiency (7.01%). This high efficiency was due to the high grain size and low band gap energy.