Chemical vapor deposition growth and photodetector performance of lead-free all-inorganic crystalline Cs₃Sb₂X₉ (X = I, Br) perovskite thin films

Lead-based organic or inorganic halide perovskites (ABX₃, A = organic or inorganic cation, B = lead cation, and X = Cl, Br, I) are well-known for their excellent properties and are technologically suitable for many optoelectronic devices. However, the stability of organic hybrid compounds and the toxicity of lead (Pb) inhibit the development and commercialization of these devices. Consequently, Pb-free, all-inorganic halide perovskites are now the subject of the recent research interest. In this work, we report on the synthesis and properties of Pb-free all-inorganic Cs₃Sb₂X₉ (X = I, Br) perovskite thin films by a two-step CVD approach. The obtained Cs₃Sb₂I₉ and Cs₃Sb₂Br₉ thin films show good crystallinity and exhibit high exciton binding energies with large Stokes shifts of ∼570 and ∼630 meV, respectively. Refractive indices of 2.0 and 1.7 were obtained for Cs₃Sb₂I₉ and Cs₃Sb₂Br₉ thin films at their respective emission energies. The optical bandgaps were confirmed to be 2.2 and 2.85 eV for Cs₃Sb₂I₉ and Cs₃Sb₂Br₉ thin films. Photoconductive devices fabricated using these thin films exhibit commendable performance with responsivity of up to 54.5 and 3.6 mA W⁻¹ and high detectivity reaching 4.3 × 10¹⁰ and 1.6 × 10¹⁰ Jones for Cs₃Sb₂I₉ and Cs₃Sb₂Br₉, respectively. Moreover, a stable photoswitching property with fast rise and decay times of 50 ms and 30 ms for Cs₃Sb₂I₉ and 108 ms and 56.2 ms for Cs₃Sb₂Br₉ film photodetectors was observed. The thin films exhibit excellent long-term stability even when stored without encapsulation in ambient air. The properties of these crystalline Cs₃Sb₂X₉ perovskite films and their photodetector performance suggest that they can be promising candidates for a wide range of optoelectronic devices.