Annual energy yield of 2T and 4T perovskite/poly-SiO_x tandem for (a) varying perovskite thickness (perovskite bandgap is fixed to 1.68 eV for 2T and 4T tandem) and (b) varying perovskite bandgap (perovskite thickness is fixed to 550 nm for 2T and 700 nm for 4T). The 4T and 2T poly-SiO_x simulations have been carried out at Rome at an optimum tilt of 27°. The blue circles indicate the optimal perovskite thickness and bandgap respectively.