# Efficiency Enhancement of GaAs Single-Junction Solar Cell by Nanotextured Window Layer
## 3 Results
Enhanced EQE affects current density (J) improvement, as in Equation (1):  
\[EQE=\frac{I/e}{P_{0}/hc}=\frac{JA/e}{P_{0}/hc} \tag{1}\]  
where \(I\) is the current, \(e\) is the charge of one electron, \(P_{0}\) is the total power of photons, \(h\) is the Planck constant, \(c\) is the speed of light, and \(A\) is the surface area of the device receiving the light. As a result, the improved J spectra of the ARC and NT SC compared to the bare surface SC was represented, as shown in Figure 6. The EQE of the ARC and NT SC increased similarly from the bare surface SC with no conspicuous offset between each other as shown in Figure 5; the J-V curves as plotted in Figure 6 reveal that the J of the ARC and NT SC increased with no conspicuous offset from the bare surface SC. Figure 5: EQE for the bare surface SC, SC with SiN\({}_{\rm x}\) ARC, and InAIP NT surface. Figure 6: J–V curves for the bare surface SC, SC with SiN\({}_{\rm x}\) ARC, and InAIP NT surface. The specific measured device parameters from the J-V curves, as shown in Figure 6, are summarized in Table 1. In order to investigate the effect of the NT surface on GaAs 1J SC, the photovoltaic J-V characteristics were measured. As the bare surface SC for reference, the improved J was the main factor to increase \(\eta\). As shown in Figure 4, the NT surface has a lower reflectance in a wider absorption wavelength range than that of the ARC surface, but the reflectance of the ARC surface is less in the wavelength band near the GaAs energy bandgap. As shown in Figure 5, the EQE of NT solar cells is greater than that of ARC solar cells, but the EQE of ARC solar cells is larger in the wavelength band near the GaAs energy bandgap. As a result of the reflectance and quantum efficiency, the current density of the NT solar cell is slightly lower than that of the ARC solar cell, but the open circuit voltage is slightly increased. As shown in Figure 7, efficiencies were acquired with varying \(\theta\) from 0 \({}^{\circ}\)C to 70 \({}^{\circ}\)C at intervals of 10 \({}^{\circ}\)C. The \(\eta\) of the NT SC is apparently higher than the \(\eta\) of the ARC SC at all ranges of \(\theta\). The \(\eta\) of the NT SC from 0 \({}^{\circ}\)C to 20 \({}^{\circ}\)C was almost preserved and the gaps of \(\eta\) between the NT and ARC SC were gradually wider from 50 \({}^{\circ}\)C to 70 \({}^{\circ}\)C. The \(\eta\) at 70 \({}^{\circ}\)C of the NT SC was about 3.2 times higher than the \(\eta\) of the ARC SC. It demonstrates that the NT surface alleviates the loss of \(\eta\) as \(\theta\) increases compared to the planar ARC surface. Since the dimensions of nanotextures are increased in the bottom, the scattering effect becomes increasingly pronounced, and the incident photons are more likely to bounce back and forth among the NT surface. As a result, the optical path on the solar cell surface is prolonged, leading to enhanced absorption by the active region while \(\theta\) is modified. Hence, the three-dimensional NT surface is distinguished from the planar ARC surface. It was found that NT SC has omnidirectionality.