Halide perovskites are soft, ionic semiconductors with exceptional optoelectronic properties. They typically have direct bandgaps in the visible spectrum that can be tuned by composition. For example, MAPbI₃ has a direct bandgap of about 1.5–1.6 eV, while replacing I⁻ by Br⁻ or Cl⁻ raises the gap to approximately 2.3 eV (green emission) or about 3.0 eV (blue) respectively. Depending on the halide used, the band gap can be tuned from around 1.6 eV (I) to approximately 3.2 eV (Cl). Mixed-halide perovskites allow continuous tuning across this range.

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