Annual energy yield of 2T bi-facial tandem modules based on SHJ or poly-SiO_x bottom cells in (a) Reykjavik, (b) Rome and (c) Alice Springs for different reflecting materials (dry grass, green grass, white paint and snow). Results are compared with mono-facial configuration. The perovskite absorber thickness is set to 700 nm (550 nm) for SHJ-based (poly-SiO_x-based) tandem module. Its bandgap is 1.68 eV. Optimized tilt is considered for each location (Tab. 3).