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

As an alternative to lead-based perovskites, Cs2AgBiBr6 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 Cs2AgBiBr6 thin film via chemical vapor deposition (CVD). By tuning the growth temperature, we successfully obtained Cs2AgBiBr6 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 A1g mode was used to determine the thermal stability of the as grown film and to estimate the temperature coefficient of the A(1g) mode (a similar to -0.01431 +/- 0.0039 cm(-1) K-1) in the Cs2AgBiBr6 thin film. Power-dependent Raman spectral analysis was employed to evaluate the thermal conductivity of suspended Cs2AgBiBr6 as similar to 1.97 +/- 0.48 W/m-K. A detailed study of the electron-phonon and phonon-phonon interactions in the Cs2AgBiBr6 DP system was carried out. Additionally, due to its excellent absorption in the UV-vis region and long carrier lifetime, the CVD-grown Cs2AgBiBr6 film on a SiO2 substrate was utilized as a photodetector. The planar photodetector device, in addition to being self powered, exhibited a fast photoresponse of similar to 170/177 mu s, which is far superior to that of Cs2AgBiBr6-based photodetectors reported to date. Thus, this work paves the way for the direct CVD growth of highly compact and uniform Cs2AgBiBr6 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.