# Photovoltaic Solar Cells: A Review
## 3 Simulation of Solar Cells and Modules
### Simulation of Solar Cells by MATLAB/Simulink  
MATLAB/Simulink is an important mathematical environment for implementation of equations required for modelling PV cells. With the aid of computer-based tools, the efficiency of PV solar cells can be improved. The mathematical modelling in MATLAB includes the following procedures [92, 93, 94, 95]. First, modelling the photocurrent \({}^{\prime}I_{ph}\)' according to the following equation:  
\[I_{ph}=[I_{sc}+K_{i}(T-298)].\ G/1000 \tag{14}\]  
where \({}^{\prime}K_{i}\)' is the temperature coefficient of '\(I_{sc}\)'; T: operating temperature (K); '\(G\)': solar insolation representing a full-sunlight condition as the illumination of sunlight varies widely in intensity and spectrum [96]. Second, modelling the reverse saturation current \({}^{\prime}I_{rs}\)' as follows:  
\[I_{rs}=I_{sc}/e\ \frac{(\frac{\pi\,I_{sc}}{\Delta\,\textit{s}\,\textit{d}\, \textit{K}})}{(\textit{s}\,\textit{d}\,\textit{K}\,\textit{d}\,\textit{K})}-1 \tag{15}\]  
\({}^{\prime}N_{s}\)' is the number of cells connected in series and '\(n\)' is the ideality factor of the diode. The saturation current \({}^{\prime}I_{0}\)' varies with the cell temperature, which is expressed by:  
\[I_{0=}I_{rs}.(\ T/T_{n})^{3}.\exp\big{[}\ q.E_{g}.(1/T_{n}-1/T)/n.k\ \big{]} \tag{16}\]  
\({}^{\prime}T_{n}\)' is the nominal temperature (298.15 K). Moreover, the current through the shunt resistance \({}^{\prime}I_{sh}\)' is simulated by [97]:  
\[I_{sh}=(v.Np/Ns+(I.R_{s})/R_{sh} \tag{17}\]  
\({}^{\prime}N_{p}\)' is the number of cells connected in parallel. Finally, the output current \({}^{\prime}I\)' of the PV cell is given by:  
\[I=I_{ph}-I_{0}\ \cdot[exp\ (q.\bigg{(}v+\frac{I.R_{s}}{n}.K\.N_{s}.\ T-1 \bigg{]}-I_{sh} \tag{18}\]  
The extracted results would be I-V and P-V characteristics at different input parameters and conditions, such as weather conditions (temperatures and radiation), solar cell design, and employed materials [98, 99]. The characteristics of solar cells under varying radiation conditions were investigated in [100, 101, 102, 103], which reported that the output power increases with the intensity of solar radiation. Figure 9 presents the effect of irradiance on the electrical characteristics of single-junction GaAs solar cells at 25 \({}^{\circ}\)C cell temperature. Furthermore, many studies such as [104; 105] stated that the efficiency of solar cells decreases with an increase in the cell temperature even though the current slightly increases as the voltage drops leading to a drop in the obtained power (Figure 9). Moreover, it was found that the performance of solar modules is affected by the parasitic resistances '\(R_{s}\)' and '\(R_{sh}\)'. For ideal PV performance, '\(R_{sh}\)' must be as high as possible while '\(R_{s}\)' must be as low as possible [94], referring to Figure 10.  
A previous study by [101] focused on modelling a multi-junction solar cell (MJSC) of InGaP/GaAs/Ge using MATLAB/Simulink to compare with standard Si solar cells. The results showed that the tandem cell can provide nearly three times higher maximum power compared to the typical Si PV cells. Another study [98] was performed on InGaN p-i-n solar cells using MATLAB/Simulink by altering the physical proprieties of the cell as well as the parasitic components under different conditions. The developed model showed promising and accurate results, validated by experimental results. Furthermore, [103] developed a MATLAB/Simulink model to generate solar radiation at any location and for any time of the year. The generated solar data were fed to the PV module to get practical results of the output power at any location and time. Hence, the mathematical modelling of PV cells in MATLAB/Simulink helps to investigate the I-V and P-V characteristics and enhance the PCE of solar modules. Figure 10: The impact of (a) series resistance (b) shunt resistance on the P-V characteristics of single-junction GaAs cells under AM 1.5 condition.