Goldschmidt-rule-deviated perovskite CsPbIBr2by barium substitution for efficient solar cells

All-inorganic Br-rich perovskite photovoltaics with excellent stability have gained ever-increasing attention despite their slightly lower efficiency. Nowadays, trace heteroatom substitution has become a plausible approach to optimize perovskite properties as well as device performance. However, the substitution is limited by the Goldschmidt tolerance factor (t, 0.8 < t < 1.0), leading to the situation that the alternative deviating from the Goldschmidt rule is always overlooked, let alone utilized to enhance performance. Given this, Ba(II) is partially substituted for Pb(II) in CsPbIBr2 to investigate how the dopants-induced deviation from the Goldschmidt rule would affect perovskite property. Intriguingly, the result verifies that Ba(II) enables increased the grain size and enhances the crystallinity of CsPbIBr2. As such, the trap state density is reduced and the non-radiative recombination in the perovskite is suppressed. These advantages bring about an increase of the power conversion efficiency (PCE) of Ba(II)-doped devices to 10.51%, outperforming that (8.4%) of the pristine counterpart. In addition, the perovskite stability is immune to Ba(II) substitution, even though it inflates the perovskite crystal lattice. These findings indicate that the perovskite films are tolerant to homovalent heteroatoms with a larger radius, stimulating further development of perovskite substitution engineering.