Surface Defects Passivation with Organic Salt for Highly Stable and Efficient Lead-Free Cs₃Sb₂I₉ Perovskite Solar Cells

Abstract

Poor stability and high toxicity are the primary challenges to the further development of Pb-based perovskite solar cells. To this end, the scientific community has paid increased attention to lead-free perovskites such as cesium antimony iodide (Cs3Sb2I9), which have demonstrated high stability. However, the charge recombination that arises from deep-level defects in Cs3Sb2I9-based solar cells results in low power conversion efficiencies (PCEs). Therefore, adding passivation or additives such as triiodide ions (I3 –) could be viable for achieving homogeneous, compact, and defect-free perovskite films. Herein, we develop a facile approach for eliminating surface defects in Cs3Sb2I9 solar cells. Light irradiation of formamidinium iodide (FAI), the generated FA+ and I3 – ions, improves the grain size, crystallinity, and surface morphology of the film, thus decreasing the nonradiative defects in films. Furthermore, a high-quality Cs3Sb2I9-based perovskite-layered phase is achieved at a low temperature (>100 °C). With a hole-transport layer-free architecture (glass/FTO/c-TiO2/Cs3Sb2I9/Au, where FTO = fluorine-doped tin oxide), the PCE is boosted from 1.06 to 1.76% with good long-term stability in an ambient environment. Additional physical characterizations evidenced the passivation of detrimental defects, reduction of charge recombination, and efficient charge transfer, which contribute to enhanced device performance. We believe such a facile approach could pave the way for the widespread development of highly stable Pb-free perovskite solar cells.

Lead‐Free All‐Inorganic Cesium Bismuth Iodide‐Based Perovskite Solar Cells: Recent Advances, Current Limitations, and Future Prospects

“…[76,102] In particular, Sb-based halide perovskites with analogous properties and lower exciton binding energy as compared with Bi-based counterparts have attracted increasing attention as light absorbers for PSCs. [43,45] The Pb 2þ cations were replaced by trivalent Sb 3þ in traditional ABX 3 perovskite to form the more stable A 3 B 2 X 9 structure. As for the Sb-based PSCs, Zhang et al fabricated Cs 3 Sb 2 Cl x I 9-x films by introducing methylamine chloride as an additive in the solution-based route, exhibiting a high PCE of 3.2% in normal PSCs.…”

“…[44] Nevertheless, the hightemperature treatment of Cs 3 Sb 2 I 9 (250 °C) may impact the reproducibility of PSCs. [43] In addition, the existence of highconcentration deep-level defects of Cs 3 Sb 2 I 9 led to serious nonradiative carrier recombination, limiting the further PCE enhancement of corresponding PSCs. [43,103] Therefore, Bi-based halide perovskites may be highly attractive and diverse choices as light absorbers for PSCs in terms of different dimensions (3D, 2D, 1D, and 0D) with various formulas of A 3 Bi 2 X 9 , A b BiX bþ3 , ABi a X 3aþ1 , and A 2 BBiX 6 .…”

“…[43] In addition, the existence of highconcentration deep-level defects of Cs 3 Sb 2 I 9 led to serious nonradiative carrier recombination, limiting the further PCE enhancement of corresponding PSCs. [43,103] Therefore, Bi-based halide perovskites may be highly attractive and diverse choices as light absorbers for PSCs in terms of different dimensions (3D, 2D, 1D, and 0D) with various formulas of A 3 Bi 2 X 9 , A b BiX bþ3 , ABi a X 3aþ1 , and A 2 BBiX 6 . [5] In these Bi-based halide perovskites, double perovskites (Cs 2 AgBiBr 6 ) exhibiting outstanding structural stability, long carrier lifetime, and superior thermal/humid stability have shown great potential in perovskite photovoltaics.…”

“…[40][41][42] In addition, the high-temperature treatment for the fabrication of Sb-based perovskite films also strongly limited the further performance enhancement and reproducibility of Sb-based PSCs. [43][44][45] Therefore, it is critical to seek stable alternatives with similar properties to Pb-based halide perovskites. Besides the aforementioned cations, bismuth cation (Bi 3þ ) is also considered as a promising alternative to substitute Pb 2þ due to the similar 6s 2 6p 0 electronic configuration and comparable electronegativity/ionic radius to those of Pb 2þ , exhibiting similarly physical and chemical properties.…”

Doping strategies for inorganic lead-free halide perovskite solar cells: progress and challenges

“…The addition of SnF 2 improves photovoltaic performance by reducing Sn vacancies. Farooq et al 119 eliminated surface defects in solar cells by adding formamidine iodide (FAI) during the synthesis of Cs 3 Sb 2 I 9 solar cells. Light irradiation of FAI generates FA + and I 3 − ions, and improves the grain size, crystallinity, and surface morphology of the thin film, thereby reducing non-radiative defects in the film, resulting in an increase in the PCE from 1.06% to 1.76%.…”