## 3 Results and Discussion
The limited rear incident light resulting from the highest absorption of  
Figure 2: I–V Characteristics of None, Flat, and Textured reflectors under various conditions: (**a**) 10 mm of D\({}_{\text{RR}}\) and 5 mm of D\({}_{\text{Gap}}\), (**b**) 30 mm of D\({}_{\text{RR}}\) and 5 mm of D\({}_{\text{Gap}}\), (**c**) 10 mm of D\({}_{\text{RR}}\) and 10 mm of D\({}_{\text{Gap}}\), and (**d**) 30 mm of D\({}_{\text{RR}}\) and 10 mm of D\({}_{\text{Gap}}\). the incident light by the black surface contributes to these similar values. Here, the small deviations in PCE and I\({}_{\text{SC}}\) observed in the none group might be attributed to the imperfect black surface, which does not absorb the entire incident light. Conversely, the implementation of a rear reflector improves the I\({}_{\text{SC}}\) and PCE of bPVs. Photons passing through the gap between cells bounce off the rear reflector, providing additional opportunities to harvest in the rear side of bPVs. The improved I\({}_{\text{rear}}\) contributes to improvement in I\({}_{\text{SC}}\) and PCE of the bPV with the proposed textured reflector (Textured). The textured reflector exhibits a more effective transfer of transmitted photons to the cells compared to the flat reflector with increased \(\eta_{\text{Opt}}\) in all cases. Although the I\({}_{\text{SC}}\) enhancement ratio introduction of the textured reflector to the bPV varies depending on the D\({}_{\text{RR}}\) and D\({}_{\text{Gap}}\), the textured reflector consistently outperforms the one with the flat reflector (Flat). For example, under conditions where both D\({}_{\text{RR}}\) and D\({}_{\text{Gap}}\) are set at 10 mm, the I\({}_{\text{SC}}\) and PCE of the flat reflector are 1.016 A and 18.8%, respectively. In the same conditions, those of the textured reflector increased to 1.034 A and 19.3%, as shown in Figure 2c. If the \(\eta_{\text{shading}}\) is around 40% due to off-axis incident light from the imperfect optical system of the solar simulator and bPV including experimental system, \(n_{\text{Opt}}\) values for the textured and flat reflectors, as calculated from Equation (1), are 0.53 and 0.35, respectively. This indicates that the textured reflector enables 1.5 times more light to be transferred to the rear side of the bPV. These effects are more pronounced in the bPVs with larger D\({}_{\text{Gap}}\) and longer D\({}_{\text{RR}}\). As the D\({}_{\text{Gap}}\) increases, more light passes through the gap between cells through the enlarged A\({}_{\text{Gap}}\) in the bPVs and reaches the reflector. The textured surface alters the trajectory of the transmitted light, increasing the chances of unabsorbed photons returning to the rear side of the bPV. The extended D\({}_{\text{RR}}\) allows more transmitted light to be collected at the rear side of the bPV, broadening the possible reflection angle to reach the rear side of the bifacial cell. On the other hand, it is challenging to change the direction of reflective light in the flat reflector. Most normal incident photons impinging on the flat reflector escape from the module through the gap between cells without altering their trajectory. Although the specular reflective flat reflector redirects part of the incident light to the rear side of the bPVs, the ratio of redirected light to the bPV is lower than that of the textured reflection, resulting in reduced I\({}_{\text{SC}}\) and PCE of the flat reflector compared to those of the textured reflector. The textured reflector shows better PCE and I\({}_{\text{SC}}\) (19.6% and 1.060 A, respectively), when D\({}_{\text{RR}}\) and D\({}_{\text{Gap}}\) are at 30 and 10 mm, respectively. Assuming an \(\eta_{\text{shading}}\) of 30%, the calculated \(\eta_{\text{Opt}}\) for the textured reflector is 0.58. The improved \(\eta_{\text{Opt}}\) for the textured reflector reflects the enlarged subtended angle, which allows more reflected light to reach the rear side of the bPV.