0D/2D Mixed Dimensional Lead-Free Caesium Bismuth Iodide Perovskite for Solar Cell Application

Abstract

Bismuth-based perovskites are potentially a promising alternative for lead-free perovskites. During bond formation, however, trivalent ions on Cs3Bi2I9 with CsI/BiI3 ratio of 1.5/1 form 0D-neutral charged compounds with higher bandgap (>2.0 eV) and poor absorption capacity. Mixed 0/2-dimensional structures are potentially suitable substitutes due to their low bandgap. So far, the reported CsI/BiI3 ratios for 0D/2D structures are 1:1, 1:2 and 1:3. Herein, a new ratio of 1/1.5 is reported. Caesium bismuth iodide at a ratio of CsI/BiI3 of 1/1.5 was synthesised using a one-step processing method with/without solvent vapour annealing. During solvent annealing, a 1/4 (v/v) mixture of DMF/methanol was used as a solvent. The crystal structure formed at a ratio of 1/1.5 is more similar to 1.5/1 than to 1/3. The XRD pattern revealed additional characteristics peaks at 009, 012, 209 and 300, indicating the growth of another phase. The formed heterogeneous mixed 0D/2D structure has an extended light absorption capacity greater than 720 nm. Solvent vapour annealing improved film morphology by enhancing grain size and packing density. When cells with and without solvent vapour annealing are compared, the power conversion efficiency of caesium bismuth iodide increases from 0.26% without solvent annealing to 0.98% with solvent vapour annealing. This study establishes a new route for future research on crystal configuration, nomenclature, film and morphology, quality tailoring and applications toward the goal of lead-free perovskite solar cells.

Potassium Iodide-Modified Lead-Free Cs3Bi2I9 Perovskites for Enhanced High-Efficiency Solar Cells

“…Table 1 shows two polymorphs in trivalent cation-based Cs₃Bi₂I₉ lead-free perovskites: 0-dimensional (dimer, P6 3 /mmc) and 2-dimensional (layered, P3m1) phases. The 2D phase is favored for carrier transport [ 1 , 37 ] due to its narrower bandgap, although maintaining this phase at an ambient temperature is difficult.…”

Blended bismuth-based Cs3 Bi2 I9 /Ag2 BiI5 perovskite films incorporated potassium iodide for high-efficiency carbon electrode solar cells

“…2f, cross-sectional SEM images. The enhancement of charge carrier mobility in the perovskite layer should result from this better crystal grain structure [52]. Also, as can be seen in Fig.…”

A versatile approach for the immobilization of lead-free Cs3Bi2I9 perovskites for photocatalytic CO2 reduction

“…Two additional bands centered at 400 and 665 nm were observed in the M-CBI sample. Previous works have also observed additional excitation bands on Cs 3 Bi 2 I 9 spectra, which could be derived from the light-induced excitation from the valence to the conduction band from occupied I p with a small contribution of Bi s states into empty Bi p + I p states [20,21]. Also, the excitation band around 665 nm (1.8 eV) has been related to the presence of layered structure of the Cs 3 Bi 2 I 9 similar to BiI 3 [22], which could suggest a lower purity of the hexagonal structure of this perovskite.…”