Synthesis, crystal structure, optoelectric properties and theoretical study of three perovskite-like iodobismuthate charge-transfer salts based on butylpyridinium

Abstract

Three new perovskite-like iodobismuthate hybrids with two butylpyridinium cations, namely (BPY)3(Bi2I9) (1), (BPY)5(Bi2I11) (2) and (BMPY)3(Bi2I9) (3) (BPY ​= ​1-butylpyridinium, BMPY ​= ​1-butyl-4-methylpyridinium), were synthesized by reacting of BiI3 and butylpyridinium. Single-crystal X-ray diffraction analysis revealed that these three hybrids exhibit two types of di-nuclear cluster structures, face-sharing Bi2I93− cluster for 1 and 3, and vertex-sharing Bi2I115− cluster for 2. Their optical band gaps were determined as 2.06 ​eV(1), 2.01 ​eV(2), 1.86 ​eV(3), respectively. DFT calculation reveals that their valence band tops and conduction band bottoms are composed of the states of iodine and pyridinium cations, respectively. Therefore these materials were classified as charge-transfer salts. Compared with similar iodobismuthates, their band gaps are significantly reduced. In addition, it is found that the band gaps should be affected by supramolecular interaction between cations in 2 and also by the conformational multiplicity of cations in structure 3. Photocurrent response test showed that these charge-transfer salts have rapid and consistent photocurrent response. This result indicated their potential applications as a photocatalyst or a photovoltaic absorber.