Optimized bandgaps of top and bottom subcells for bifacial two-terminal tandem solar cells under different back irradiances

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Detailed balance limit is calculated for bifacial two-terminal tandem (double-junction) solar cells. The solar cells are considered as blackbody with temperature of 298.15 K and front illumination of air mass (AM)1.5G spectrum as well as back illumination of effective albedo (RA) × AM1.5G spectrum. Under spectral independent RA, ((Front Irr + Back Irr)/Front Irr) is defined as a ratio of (front irradiance + back irradiance) to front irradiance. Optimized bandgaps for bottom subcell (Eg-bottom) and top subcell (Eg-top) of the bifacial tandem solar cells are revealed to match photogenerated current densities of two subcells, thereby yielding their maximum output power under varying ((Front Irr + Back Irr)/Front Irr). Moreover, it is disclosed that the current mismatching in monofacial perovskite/silicon tandem solar cell can be solved by the structure of the bifacial perovskite/silicon tandem solar cell with suitable (Front Irr + Back Irr)/Front Irr. Therefore, bifacial perovskite/silicon tandem solar cell generates more output power up to 66% than its monofacial counterpart despite low (Front Irr + Back Irr)/Front Irr of 1.244 (or RA of 0.244). The optimized Eg-bottom is additionally disclosed in bifacial tandem solar cell with Eg-top (perovskite top subcell) of 1.55 eV, as well as optimized Eg-top is revealed with Eg-bottom (silicon bottom subcell) of 1.12 eV under different (Front Irr + Back Irr)/Front Irr values.