Influence of the Iodide to Bromide Ratio on Crystallographic and Optoelectronic Properties of Rubidium Antimony Halide Perovskites

Abstract

Rubidium antimony halides are a promising low toxic alternative to organo-lead halide perovskites as photovoltaic material. In this contribution, we systematically investigate the influence of varying the bromide to iodide ratio on the structural, optical, and photovoltaic properties of Rb3Sb2­Br9–x I x (x = 0–9). Single crystal data reveal that all compounds crystallize in a 2D-layered monoclinic crystal structure. Sequential substitution of iodide with the smaller bromide does not change the crystal system; however, increasing the bromide content results in a shrinkage of the unit cell as well as in a blue shift of the absorption onset, increasing the band gap from 2.02 to 2.46 eV. Whereas the photovoltaic properties of bromide rich compounds are limited due to a preferential orientation of the layered structure parallel to the substrate, which is detrimental to charge transport, solar cells with Rb3Sb2I9 as absorber material display power conversion efficiencies of 1.37%. Moreover, the devices exhibit low hysteresis properties and are stable for more than 150 days stored under inert atmosphere.

Dependence of material properties and photovoltaic performance of triple cation tin perovskites on the iodide to bromide ratio

“…2c). This is in accordance with Vegard's law [29], and similar linear correlations have been also observed, e.g., for mixed halide lead or antimony perovskites [30][31][32][33].…”

“…Both the optical band gap and the lattice constants show a linear dependence on the bromide content. Thus, in this regard, the herein presented Sn analogues behave very similar to other perovskite systems, e.g., based on lead halides [32,33] or antimony halides [31]. The J-V characteristics of the fabricated perovskite solar cells with x = 0-0.33 revealed an increase in V OC from 0.37 to 0.49 V as expected due to the increase in the optical band gap.…”

Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs3Sb2ClxI9–x 2D‐Layered Perovskites

“…This result is a first indication of structure preservation across the series and is distinctly different than the dramatic bandgap shifts found in Rb 3 Cs 3 Br x I 9 – x . [ 28 ] However, the light absorption at shorter wavelength of 2D‐Cs 3 Sb 2 Cl x I 9 – x films was gradually enhanced with chloride incorporation due to the integrated effects of better crystallinity and larger sizes of grains. Meanwhile, the light absorption at shorter wavelength was weakened for higher chloride content ( x = 1.06), which is attributed to the deteriorated morphology (presence of pinholes) and slightly increased bandgap of 2D‐Cs3Sb2Cl x I 9 – x film with x = 1.06.…”

“…In 2019, Weber et al studied, in detail, the structural and optoelectronic effects of substituting bromide for iodide in Rb 3 Sb 2 Br x I 9 – x and found no lattice substructure changes but significant deterioration of photovoltaic properties upon any alloying of bromide. [ 28 ] The same year, Umar et al demonstrated enhanced photovoltaic performance in Cs 3 Sb 2 I 9 using intermediate coordination of Cl ions to form the 2D phase at 160 °C, yet, no Cl − remained in the final film. [ 29 ] Very recently, Peng and co‐workers experimentally verified Jiang's predictions with Cs + at the A‐site; they indeed observed a transition from 0D to 2D at low solution processing temperatures (135 °C) by tuning the initial ratios of I‐ and Cl‐containing precursors and have achieved a PCE of 2.15% for n‐i‐p architecture.…”

Microstructural and photoconversion efficiency enhancement of compact films of lead-free perovskite derivative Rb3Sb2I9

“…achieved a PCE of 1.37%. 37 Interestingly, the more-than-twofold increase in PCE of the latter work comes with a slightly lower EQE (26%). 37 It is noteworthy that all these studies adopt a device architecture in which Rb 3 Sb 2 I 9 is grown on (and partly embedded in) a mesoporous electron transport layer.…”