Perovskite solar cells were the subject of a current commentary, previously published in this journal~1 These are solar cells whose structure utilises a perovskite-type compound as the light-harvesting active layer~1. The term 'perovskite solar cell' originates from the ABX_3 stoichiometry of the absorber materials, which translates to a perovskite crystal structure (Figure 1). The most extensively studied absorber material is methylammonium lead trihalide (CH_3NH_3PbX_3; where X is a C1, Br or I atom), with a bandgap energy in the range of 1.5-2.3 eV. The related material, formamidinum lead trihalide (H_2NCHNH_2PbX_3) is also promising, with bandgaps that occupy the range 1.5-2.2 eV. Indeed, since the smallest bandgap approaches more closely the optimum value for a single-junction cell than does methylammonium lead trihalide, it is expected that higher efficiencies might be attained using these materials~2. It has been shown that the bandgap in the methylammonium lead.
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