A mixed cation lead mixed halide perovskite absorber for tandem solar cells
Perovskites for tandem solar cells Improving the performance of conventional single crystalline silicon solar cells will help increase their adoption. The absorption of bluer light by an inexpensive overlying solar cell in a tandem arrangement would provide a step in the right direction by improving overall efficiency. Inorganic organic perovskite cells can be tuned to have an appropriate band gap, but these compositions are prone to decomposition. McMeekin et al. show that using cesium ions along with formamidinium cations in lead bromide iodide cells improved thermal and photostability. These improvements lead to high efficiency in single and tandem cells. Science, this issue p. 151 Addition of cesium cations creates a robust ideal inorganic organic perovskite absorber for tandem silicon solar cells. Metal halide perovskite photovoltaic cells could potentially boost the efficiency of commercial silicon photovoltaic modules from ~20 toward 30% when used in tandem architectures. An optimum perovskite cell optical band gap of ~1.75 electron volts (eV) can be achieved by varying halide composition, but to date, such materials have had poor photostability and thermal stability. Here we present a highly crystalline and compositionally photostable material, [HC(NH2)2]0.83Cs0.17Pb(I0.6Br0.4)3, with an optical band gap of ~1.74 eV, and we fabricated perovskite cells that reached open circuit voltages of 1.2 volts and power conversion efficiency of over 17% on small areas and 14.7% on 0.715 cm2 cells. By combining these perovskite cells with a 19% efficient silicon cell, we demonstrated the feasibility of achieving >25% efficient four terminal tandem cells.
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