Tuning Self-Trapped Exciton States via Trivalent-Metal Alloying in Lead-Free 2D Double-Perovskites

Strong carrier-phonon coupling-induced self-trapped excitons (STEs) limit the application of 2D double-perovskites in optoelectronic devices because the separation and collection of the highly localized STEs are challenging. In this study, antimony (Sb) is incorporated into (BA)(4)AgBiBr8 (BA = CH3(CH2)(3)NH3+) to form (BA)(4)AgSbxBi1-xBr8 (0 <= x <= 1) trivalent-metal alloyed 2D double-perovskites. It is found that introducing Sb into the (BA)(4)AgBiBr8 2D double-perovskite will decrease the carrier-phonon coupling strength and change STEs from dark states to bright states at room temperature. Combining detailed spectroscopic analysis with density functional theory calculation, it is concluded that STEs localized at [SbBr6] octahedron in (BA)(4)AgSbxBi1-xBr8 give the broadband bright emission. The bright STEs with moderate carrier-phonon coupling opens the possibility to efficiently separate and collect charge-carriers in (BA)(4)AgSbBr8 2D double-perovskites. Photodetectors based on (BA)(4)AgSbBr8 crystals are further fabricated. The photodetectors exhibit high responsivity up to 1368 A W-1 and an external quantum efficiency of 4.7 x 10(5). These figures are over three times higher than that in (BA)(4)AgBiBr8-based photodetectors. This study provides a unique strategy for developing high-performance optoelectronic devices based on STEs.

Automated summary

This study investigates the introduction of antimony (Sb) into 2D double-perovskites to change self-trapped excitons from dark to bright states. The research shows that the introduction of Sb reduces the carrier-phonon coupling strength, allowing for efficient separation and collection of charge-carriers. Photodetectors based on the modified material exhibit significantly higher responsivity and external quantum efficiency compared to those based on traditional 2D double-perovskites. This study presents a unique strategy for developing high-performance optoelectronic devices utilizing self-trapped excitons.