## 2 Experiments and Methodology  
### Fabrication of bPV with Textured Reflector  
The fabrication process of the textured reflector is illustrated in Figure 1a. The textured surface was made by an Ethylene vinyl acetate (EVA) sheet positioned on a clean glass surface. EVA is commonly employed as an encapsulant for PV modules due to its robust mechanical adhesion to glass and high resistance to moisture, elevated temperatures, and UV light. As a result, the production of a textured surface with EVA can be obtained at the current photovoltaic module production line without a significant change. Following the removal of any dust particles, the EVA film underwent annealing at 150 \({}^{\circ}\)C for 10 min at a low vacuum. Subsequently, the molten EVA was pressed by a metal mesh (thickness of 1 mm with a 10 \(\times\) 10 mm pattern) under high pressure (760 mm Hg) for 5 min. Throughout the hot-press process, the part of EVA film pressed by the metal mesh descended, causing the residual EVA to migrate towards the center of the mesh where pressure was not applied. This resulted in the center of the mesh protruding and forming a textured surface with a height difference of 1.5 mm between the peak and valley, as depicted in Figure 1a. Here, we used EVA for the textured surface, but we believe that the textured surface can be obtained using various stable thermoplastics. After cooling the EVA film at room temperature for 1 h, the truncated cone-shaped EVA was covered by a printable silver ink (TEC IJ-060 from InkTec, Ansan, Republic of Korea) [47]. The film was then annealed at 150 \({}^{\circ}\)C for 30 min to dry the solvent of silver ink. The thickness of the silver layer was ~100 \(\upmu\)m. The key advantage of this proposed process lies in the ability to generate mechanically and chemically stable textured reflectors through a low-temperature process. Due to the elimination of complicated photolithography and the high-temperature vacuum processes, the energy consumption for demonstrating the suggested textured reflectors is significantly reduced. Another notable advantage of this approach is the facile modification of the textured reflector's dimension by controlling a dimension of mold for hot pressing. While a metal mesh was used in this experiment, we anticipate that a convex-shaped mold could enable the demonstration of a hemispheric reflector [48]. Lastly, the reflective silver ink can be selectively deposited where the reflector is needed, thereby substantially minimizing silver ink wastage and rendering unintended light blocking from the rear reflector to the rear incident light negligible. Figure 1: (**a**) The schematic of the textured surface process based on a hot-pressed EVA and printable silver ink. The cross-sectional image of the textured reflector reveals the successful fabrication of a truncated cone-shaped surface through this process. (**b**) The reflectance of flat and textured reflectors is monitored by integrating sphere-incorporated spectrophotometer and a specular reflection measurement setup. The spectrophotometer within the integrating sphere measures both diffusive and specular reflections from the reflector. In contrast, the specular reflection measurement system focuses solely on specular reflection from the reflector, considering angles smaller than 5 degrees. (**c**) The experimental setup to evaluate the effect of the flat and the suggested textured reflectors on the performance of bPVs. The bPVs with and without reflectors are irradiated by the solar simulator. During the measurement process, the gap and distance of the rear reflector is controlled. The incident light irradiated the front side of bPV, while part of the light passing through the gap among the cells is reflected to the rear side of bPV. Finally, the textured reflector was integrated with a 50 \(\times\) 50 mm c-Si bPV module (laser-cut from a cell with a p-passivated emitter rear contact structure from Jinko Solar, Shanghai, China), whose bifaciality was 0.7.