Fine Structure of the Optical Absorption Resonance in Cs₂AgBiBr₆ Double Perovskite Thin Films

Abstract

The lead-free double perovskite Cs2AgBiX6 (X = Br, Cl) has recently demonstrated great potential for applications in solar cells, photodetectors, and X-ray detectors. This material is characterized by a dominant resonant absorption feature in the UV-blue spectral region, which is still under controversial discussion regarding its origin. Here, we uncover an electronic fine structure of this optical feature in Cs2AgBiBr6 thin films. A detailed temperature-resolved study combining photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy reveals the existence of three optical transitions, situated approximately 100 meV around the resonance at 2.83 eV. PL measurements under pulsed excitation uncover a short-lived blue emission at the absorption resonance energy that persists up to room temperature and indicates the competition of direct emission from the resonant state and fast relaxation into the red emissive ground state. We derive a comprehensive energy scheme and suggest possible mechanisms leading to the observed fine structure splitting.

Identifying Carrier Behavior in Ultrathin Indirect‐Bandgap CsPbX3 Nanocrystal Films for Use in UV/Visible‐Blind High‐Energy Detectors

“…It can also be observed that the absorption edge becomes very broad as the I composition increases. CsPbBr 3 NCs show a much sharper absorption edge, indicating its direct bandgap behavior, whereas perovskite containing iodine (PCI) NCs deemed as indirect bandgap, [ 44–46 ] which is in line with the the broad absorption edge and emission peaks. The corresponding Tauc plot [ 47–49 ] as shown in Figure 2b reveal the samples bandgap ranges from 2.15 eV (CsPbI 3 ) to 2.46 eV (CsPbBr 3 ).…”

Lead‐Free Halide Double Perovskites: Structure, Luminescence, and Applications

“…(e) Reproduced with permission. [ 168 ] Copyright 2020, American Chemical Society. (f) Reproduced with permission.…”

Inorganic Lead‐Free Cs2AuBiCl6 Perovskite Absorber and Cu2O Hole Transport Material Based Single‐Junction Solar Cells with 22.18% Power Conversion Efficiency

“…Among various possible double perovskite systems, Cs 2 AgBiX 6 (X = Cl, Br, and I) systems are widely explored. [ 15 ] However,Cs 2 AgBiBr 6 as an absorber in a solar cell is not very impressive (at least in the case of the single‐junction solar cells) in terms of power conversion efficiency (PCE). It is around 1.2–1.3% with Cs 2 AgBiBr 6 , whereas 1.9% PCE with sulfur modified Cs 2 AgBiBr 6 .…”

“…The poor PCE is attributed to the large indirect bandgap of 2.2 eV and poor film quality. [ 15 ] Zhang et al. reported an improvement in current and PCE with rubidium (Rb + ) doping in Cs 2 AgBiBr 6 .…”