Fig. 5. Prediction of triple junction (multi-junction) solar cells. (a) Scheme of photon energy absorption by wide and narrow bandgap perovskites in triple junctions, (b) spectral irradiance graph showing theoretical maximum power conversion efficiency bandgaps for a triple junction with a 1.22 eV narrow bandgap. (c) Theoretical efficiency limit of triple junction solar cells with a monolithic structure considering the narrow bandgap (the fixed value is 1.22 eV), intermediate bandgap (1.3–1.7 eV) and wide bandgap (1.7–2.2 eV), and (d) theoretical efficiency limit of triple junction solar cells in a monolithic architecture considering the narrow bandgap (a fixed value of 1.25 eV), intermediate bandgap (1.3–1.7 eV) and wide bandgap (1.7–2.2 eV).