Triiodide-Induced Band-Edge Reconstruction of a Lead-Free Perovskite-Derivative Hybrid for Strong Light Absorption

Bismuth-based hybrid perovskites have recently attracted great attention for their environmentally friendly processing, chemical stability, and photoresponsive properties. However, most of the known lead-free hybrids show wide band gaps (E-g > 1.9 eV) that afford weak visible-light absorption. Here, we show a newly conceptual design strategy of intercalating triiodide to decrease the prototypic band gap by ca. similar to 0.44 eV. A new hybrid semiconducting material of (4-methylpiperidinium)(4)center dot I-3 center dot BiI6 (MP-T-BiI6), adopting the zero-dimensional (0D) perovskite-like framework, was reconstructed from its prototype of (4-methylpiperidinium)(3)Bi2I9 (MP-Bi2I9). It is noteworthy that MP-T-BiI6 has a narrow band gap of 1.58 eV, almost comparable to that of CH3NH3PbI3 (similar to 1.5 eV), which reveals its potential as the highly efficient light absorber. Importantly, its semiconducting properties were solidly confirmed by notable hole mobility (similar to 12.8 cm(2) V-1 s(-1)), charge-trap density (similar to 1.13 x 1010 cm(-3)), and photoconductive behaviors. Moreover, theoretical calculations further disclose that the I-5p orbitals of triiodide induce the band-edge reconstruction and behave as a new conduction-band minimum at the Brillouin zone center. This work paves a potential pathway for the large and diverse family of lead-free hybrids to compete with lead absorbers.