Solution-Processed BiI₃ Thin Films for Photovoltaic Applications: Improved Carrier Collection via Solvent Annealing

Abstract

We report all-inorganic solar cells based on solution-processed BiI3. Two-electron donor solvents such as tetrahydrofuran and dimethylformamide were found to form adducts with BiI3, which make them highly soluble in these solvents. BiI3 thin films were deposited by spin-coating. Solvent annealing BiI3 thin films at relatively low temperatures (≤100 °C) resulted in increased grain size and crystallographic reorientation of grains within the films. The BiI3 films were stable against oxidation for several months and could withstand several hours of annealing in air at temperatures below 150 °C without degradation. Surface oxidation was found to improve photovoltaic device performance due to the formation of a BiOI layer at the BiI3 surface which facilitated hole extraction. Nonoptimized BiI3 solar cells achieved the highest power conversion efficiencies of 1.0%, demonstrating the potential of BiI3 as a nontoxic, air-stable metal-halide absorber material for photovoltaic applications.

Fabrication of Methylammonium Bismuth Iodide Layers Employing Methylamine Vapor Exposure

“…From literature, it is known that BiI 3 can also be used as photoabsorber in a dye‐sensitized solar cell with a similar device architecture used in this study . To investigate the fabricated films for unreacted BiI 3 which may also contribute to the photocurrent, UV–vis absorption spectra have been obtained from solution‐processed MBI, MBI fabricated via MA exposure at 80 °C substrate temperature, and BiI 3 reference samples (Figure , right).…”

Research Update: Bismuth-based perovskite-inspired photovoltaic materials

“…37 Two contemporary investigations of BiI 3 devices based on solution-processed thin films reported open-circuit voltages >1.3 V below the bandgap with low shunt resistances, and pinholes in the thin films may contribute to this shunting. 38,79 As well as single crystals, thin films of BiOI, with an indirect bandgap ∼1.9 eV, 35,39 have been synthesized for photovoltaic and photocatalytic applications by methods such as successive ionic layer adsorption and reaction [SILAR, Fig. 6(b)] 80 and the solvothermal method.…”

Understanding the Structural and Electronic Properties of Bismuth Trihalides and Related Compounds

“…18 Another strategy is to use the bismuth halides themselves, especially BiI 3 , which is attracting attention for photovoltaic (PV) cell applications. 19,20 However, the low dimensionality of the layered structure adopted by BiI 3 leads to a wider band gap (∼1.8 eV) 21 compared 2 with the lead-containing perovskite iodides, hence it is not ideal for PV applications. One approach to solving this problem would be to identify accessible polymorphs of the bismuth halides that retain a 3-D network architecture and should therefore have narrower band gaps.…”