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

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 (R-A) x AM1.5G spectrum. Under spectral independent R-A, ((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 R-A 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.

Automated summary

The study calculates the detailed balance limit for bifacial two-terminal tandem solar cells, revealing optimized bandgaps for matching photogenerated current densities of two subcells to maximize output power. Additionally, it is found that the current mismatching in monofacial solar cells can be solved by suitable (Front Irr + Back Irr)/Front Irr ratios.