Controlled Growth of BiSI Nanorod-Based Films through a Two-Step Solution Process for Solar Cell Applications

Abstract

Pb-based hybrid perovskite solar cells, despite their advantages, face challenges in commercialization. In recent years, Bi-based chalcohalides are being considered as potential alternative candidates, however, their current device efficiency remains unsatisfactory. Herein, a two-step solution method is developed and applied to the fabrication of BiSI films. The method consists of the formation of Bi2S3 (step I) and its conversion to BiSI (step II). The Bi2S3 was fabricated by a thiol-amine solution process and the BiSI conversion was achieved by chemical reaction between the as-formed Bi2S3 and BiI3. It was found that the formation of BiSI was highly dependent on the Bi:S molar ratio of the Bi2O3-thiourea solution and the number of times of step I. The as-fabricated BiSI film had an optical band gap of 1.61 eV and exhibited nanorod morphology. In addition, the electronic structure is explored and discussed for solar cells applications.

Recent Progress in Fabrication of Antimony/Bismuth Chalcohalides for Lead-Free Solar Cell Applications

“…Therefore, developing methods to control and optimize the properties of chalcohalides suitable for solar cells is imperative. Sb/Bi chalcohalides used for solar cells are prepared by many techniques including spray pyrolysis [ 40 ], spin coating [ 24 , 45 , 46 , 47 , 51 ], solvothermal synthesis [ 49 , 53 ], and mixed techniques [ 23 , 38 , 48 , 65 ]. In this section, the fabrication methods reported to date are categorized and described, with the solar cells fabricated presented by the method in Table 4 .…”

“…This method allowed us to fabricate pure-phase SbSI thin films and to control morphology and structure. Our method can also be applied for fabricating other chalcohalides such as BiSI [ 47 ]. To fabricate BiSI films, we introduced a Bi 2 O 3 -TU solution based on a thiol–amine solvent and BiI 3 solution in steps 1 and 2, respectively ( Figure 5 e).…”

“…The BiSI nanorods were fabricated by immersing Bi 2 S 3 -deposited tungsten (W) foil in an autoclave containing BiI 3 solution and subsequent heating. Compared to the spin coating-based two-step process [ 47 ], the as-prepared nanorods exhibited a similar E g value of 1.57 eV but showed preferential [010] orientation. To fabricate solar cells, a p-type CuSCN and an In-doped SnO 2 (ITO) were sequentially deposited on the BiSI surface, yielding a PCE of 0.66% ( Figure 6 b).…”

“… Energy band diagram of typical Sb/Bi chalcohalides. The SbSI, Sb 0.67 Bi 0.33 SI, BiSI, Pb 2 SbS 2 I 3 , and Sn 2 SbS 2 I 3 energy levels were obtained from [ 23 , 38 , 47 , 54 ] and [ 24 ], respectively. For comparison, the energy levels for typical conducting oxides (F-doped SnO 2 (FTO) and In-doped SnO 2 (ITO)), the electron transporting layer (ETL), and hole transporting layer (HTL) are included.…”

“…Following the initial application of Sb sulfoiodide (SbSI) in solar cells by the Seok group in 2018 [ 38 ], multiple Sb/Bi chalcohalide solar cells have been proposed. Thus far, the materials investigated for use in solar cells include ternary (MChX and M 13 Ch 18 X 2 , where M = Sb, Bi) [ 23 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ] and quaternary chalcohalides ( , where M II = Sn, Pb; M III = Sb, Bi) [ 24 , 54 ]. These chalcohalides commonly exhibit advantageous properties that can be adjusted for use in solar cells.…”