## 3 Results and Discussions
### Optimization of the \(InGaP/GaAs\) DjSCs with Buffer and New Top BSF Layers
#### 3.3.3 Impact of Tunnel Junction Material on the Performance of DJSCs  
The simulation of the structure of multiple junction (MJ) solar cells required the use of two distinct tunnel junction materials; a comparison between the two types of tunnel junction materials is represented in Table 7.  
Figure 10 and Table 7 highlight clearly the superior performance exhibited by the \(AlGaAs/AlGaAs\) tunnel junction compared to the \(GaAs/GaAs\) tunnel junction. \(AlGaAs/AlGaAs\) tunnel junctions exhibit superior performance compared to GaAs/GaAs junctions due to their higher bandgap, which minimizes parasitic absorption of photons and allows more light to reach the lower sub-cell. This is achieved through enhanced tunneling efficiency, which is achieved by narrower depletion widths and reduced effective carrier mass, hence facilitating higher tunneling current densities. Additionally, \(AlGaAs\) supports heavier doping concentrations with fewer defects, lowering series resistance and recombination losses. This compound material offers enhanced thermal and structural stability, improving its compatibility with \(GaAs/InGaP\) sub-cells through better lattice matching. This ensures greater long-term reliability of the solar cell. As a result, \(AlGaAs/AlGaAs\) tunnel junctions achieve maximum tunneling currents, significantly outperforming \(GaAs/GaAs\) junctions, thereby enhancing overall tandem cell efficiency. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material of Tunnel Junction** & \(J_{SC}\) **(mA/cm\({}^{2}\))** & \(V_{OC}\) **(V)** & **FF (\%)** & \(\eta\) **(\%)** \\ \hline With \(GaAs/GaAs\) tunnel junction & 20.575 & 2.319 & 85.325 & 40.704 \\ With \(AlGaAs/AlGaAs\) tunnel junction & 21.65 & 2.319 & 84.001 & 41.585 \\ Other study [5] & 17.41 & 2.45 & 88.70 & 36.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of the performance of \(InGaP/GaAs\) DJSCs between two types of tunnel junction materials. However, it is important to attract attention to the fact that the photo-generation rate (\(G\)) constitutes a central parameter for evaluating the efficiency and performance characteristics of solar cells. This rate is expressed as follows:  
\[G=\eta_{0}\left(\frac{P\lambda}{hc}\right)\alpha.\exp\left(-\alpha_{y}\right) \tag{10}\]  
where \(\eta_{0}\) is the internal quantum efficiency, \(P\) is the intensity of the illuminating ray, \(y\) is the distance traveled by the ray, \(c\) is the speed of light, \(h\) is [PERSON]'s constant, \(\alpha\) is the absorption coefficient, and \(\lambda\) is the wavelength. In this proposed model, other parameters can be extracted, as shown in Figures 11-13. Figure 11: The photo-generation rate distribution across different layers of \(InAlGaP/GaAs\) DISC. Figure 10: I–V characteristics of \(InGaP/GaAs\) DISCs with both tunnel junctions. the \(InAlGaP\) and \(InGaP\) regions, where most photon energy is absorbed before reaching deeper layers. Indeed, the \(InAlGaP\) exhibits the highest photo-generation rate due to its superior absorption coefficient (\(\alpha\)) compared to \(GaAs\) and \(InGaP\), leading to more efficient electron-hole pair generation and improved overall performance. In contrast, the \(GaAs\) region shows a lower photo-generation rate, as most light has already been absorbed by the upper layers. This highlights the importance of optimizing the thickness and material composition of these layers to maximize light absorption and hence the efficiency. These results align with previous studies emphasizing the role of material selection in enhancing solar cell performance. The spectral response is a key parameter in evaluating solar cell efficiency, representing the cell's ability to convert incident light of varying wavelengths into photocurrent and reducing the photon losses that occur at each stage due to diffusion or absorption. Whereas the spectral response can contain three current components, such as the source photocurrent, the available photocurrent, and the cathode current.