Optoelectronic properties of Rb-doped inorganic double perovskite Cs2AgBiBr6

Rubidium Doped Cs2AgBiBr6 Hierarchical Microsphere for Enhanced Photocatalytic CO2 Reduction

Halide perovskites have garnered significant attention for their unique optoelectronic properties in solar-to-fuel conversions. However, the efficiency of halide perovskites in the field of photocatalytic CO2 reduction is largely limited by serious charge recombination and a lack of efficient active sites. In this work, a rubidium (Rb) doped Cs2AgBiBr6 (Rb:CABB) hierarchical microsphere is developed for photocatalytic CO2 reduction. Experimental and theoretical analysis discloses that partially substituting Rb+ for Ag+ can effectively modulate the electronic structure of CABB, favoring charge separation and making adjacent Bi atoms an electron-rich active site. Further investigations indicated that Rb doping also reduces the energy barriers of the rate-determining step in CO2 reduction. As a result, Rb:CABB demonstrated an enhanced CO yield compared to its undoped counterpart. This work presents a promising approach to optimizing the electronic structures of photocatalysts and paving a new way for exploring halide perovskites for photocatalytic CO2 reduction.

Boosting photodetection performance of Cs2AgBiBr6 through A-site Rb substitution and interfacial engineering

Bismuth-based double perovskite Cs2AgBiBr6 shows promise as a photodetection material. However, its detection performance and application are limited by high-exciton binding energy and poor carrier mobility. In this study, we address these limitations by delicately designing a solution-based method for incorporating A-site Rubidium (Rb) substitution into Cs2AgBiBr6 double perovskite films. The introduction of Rb resulted in a significant decrease in trap defect density and an improvement in film quality. The trap-filled limit voltage (VTFL) of pure and Rb-doped CABB film is determined to be 1.71 V and 0.48 V, respectively. Subsequently, by introducing an ultrathin atomic-layer-deposited (ALD) TiO2 films, the fabricated CABB photodetectors exhibit significantly improved photoresponse performance. The response speed and -3dB bandwidth are boosted from ∼93 ms to ∼350 μs and broadened from 1.4 kHz to 17 kHz, respectively. Density Functional Theory (DFT) calculations indicate Rb-substitution shortens the bond length and weaken exciton binding energy. Furthermore, we demonstrate a wireless near ultraviolet (UV) light communication system using CABB photodetectors as light receivers. Our findings provide an efficient approach to utilize A-site cation substitution as a tuning parameter for photodetection in high-exciton binding energy perovskite materials, thereby extending the potential applications of other functional perovskites.

Lattice Expansion in Rb-Doped Hybrid Organic-Inorganic Perovskite Crystals Resulting in Smaller Band-Gap and Higher Light-Yield Scintillators

Two-dimensional hybrid-organic-inorganic perovskite (2D-HOIP) lead bromide perovskite crystals have demonstrated great potential as scintillators with high light yields and fast decay times while also being low cost with solution-processable materials for wide energy radiation detection. Ion doping has been also shown to be a very promising avenue for improvements of the scintillation properties of 2D-HOIP crystals. In this paper, we discuss the effect of rubidium (Rb) doping on two previously reported 2D-HOIP single crystals, BA₂PbBr₄ and PEA₂PbBr₄. We observe that doping the perovskite crystals with Rb ions leads to an expansion of the crystal lattices of the materials, which also leads to narrowing of band gaps down to 84% of the pure compounds. Rb doping of BA₂PbBr₄ and PEA₂PbBr₄ shows a broadening in the photoluminescence and scintillation emissions of both perovskite crystals. Rb doping also leads to faster γ-ray scintillation decay times, as fast as 4.4 ns, with average decay time decreases of 15% and 8% for Rb-doped BA₂PbBr₄ and PEA₂PbBr₄, respectively, compared to those of undoped crystals. The inclusion of Rb ions also leads to a slightly longer afterglow, with residual scintillation still being below 1% after 5 s at 10 K, for both undoped and Rb-doped perovskite crystals. The light yield of both perovskites is significantly increased by Rb doping with improvements of 58% and 25% for BA₂PbBr₄ and PEA₂PbBr₄, respectively. This work shows that Rb doping leads to a significant enhancement of the 2D-HOIP crystal performance, which is of particular significance for high light yield and fast timing applications, such as photon counting or positron emission tomography.

Interfacial Gradient-Energy-Band-Alignment Modulation via a Vapor-Phase Anion-Exchange Reaction toward Lead-Free Perovskite Photodetectors with Excellent UV Imaging Capability

Bi-based inorganic perovskites have attracted great attention in optoelectronics, as they feature similar photoelectric properties but have high stability and lead-free merits. Unfortunately, due to the high exciton binding energy and small Bohr radius, their photodetection performance still largely lags behind that of Pb-based counterparts. Herein, using a vapor-phase chloride ion-substitution strategy, Cs3Bi2Br9 photodetectors (PDs) with gradient energy band alignment were delicately modulated, contributing to a high carrier separation/collection efficiency. The optimized Bi-based perovskite ACCT (Al2O3/Cs3Bi2Br9/Cs3Bi2ClxBr9-x/TiO2) PDs exhibit outstanding performance, the ON/OFF ratio and linear dynamic range (LDR) are significantly improved by 20 and 2.6 times, respectively. Significantly, we further demonstrate the high-SNR (signal-to-noise ratio) UV imaging based on the optimized device, which shows 21.887 dB higher than that of the pristine device. Finally, the vapor-phase anion-exchange modified perovskite PDs show long-term stability and high UV resistance. Vapor-phase ion-substitution is a promising approach for the synergistic effect of matched energy band alignment and interface passivation, which can be applied to other perovskite-based optoelectronic devices.