Chemical Vapor Deposition Growth of Highly Stable Cs₂AgBiBr₆ Double Perovskite Thin Films and Their Ultralow Thermal Conductivity and Fast Photoresponse

Abstract

As an alternative to lead-based perovskites, Cs 2 AgBiBr 6 is an emerging lead-free double perovskite (DP), which has shown promise in the field of optoelectronics owing to its nontoxicity, high stability, and superior photoelectric properties. Herein, we demonstrate the growth of a highly crystalline and uniform Cs 2 AgBiBr 6 thin film via chemical vapor deposition (CVD). By tuning the growth temperature, we successfully obtained Cs 2 AgBiBr 6 thin films of high structural and compositional uniformity, confirmed by XRD, Raman, and XPS studies. Substrate-dependent growth aided the study of the induced lattice strain in the system. Temperature-dependent Raman analysis of the A 1g mode was used to determine the thermal stability of the asgrown film and to estimate the temperature coefficient of the A 1g mode (α ∼ −0.01431 ± 0.0039 cm −1 K −1 ) in the Cs 2 AgBiBr 6 thin film. Power-dependent Raman spectral analysis was employed to evaluate the thermal conductivity of suspended Cs 2 AgBiBr 6 as ∼1.97 ± 0.48 W/m-K. A detailed study of the electron−phonon and phonon−phonon interactions in the Cs 2 AgBiBr 6 DP system was carried out. Additionally, due to its excellent absorption in the UV−vis region and long carrier lifetime, the CVD-grown Cs 2 AgBiBr 6 film on a SiO 2 substrate was utilized as a photodetector. The planar photodetector device, in addition to being selfpowered, exhibited a fast photoresponse of ∼170/177 μs, which is far superior to that of Cs 2 AgBiBr 6 -based photodetectors reported to date. Thus, this work paves the way for the direct CVD growth of highly compact and uniform Cs 2 AgBiBr 6 films on arbitrary substrates with exceptional thermal and environmental stability and superior optoelectronic performance. We believe that our results will eventually provide insightful strategies for developing high-performance optoelectronic devices based on lead-free inorganic double perovskites.