Scanning the optoelectronic properties of Cs4CuxAg2−2xSb2Cl12 double perovskite nanocrystals: the role of Cu2+ content

Abstract

Double perovskite nanocrystals (NCs) have attracted much attention owing to their non-toxicity and excellent semiconducting characteristics. Herein, a series of double perovskite Cs₄Cu_xAg_2−2xSb₂Cl₁₂ NCs (x = 0.60, 0.75, 0.90, and 1.00) have been synthesized and the relationship between the Cu²⁺ content and their photo-physical properties has been investigated in detail. The temperature-dependent absorption data point out that the Cu²⁺ content can affect the transition from the indirect to direct band gap, but hardly influence the evolution of the band edge at different temperatures, which almost linearly red shifts with temperature. The transient absorption technique helps us to obtain the absorption coefficient of these double perovskite NCs. The linear and three-order nonlinear absorption coefficients, which are first measured by transient absorption (TA) and Z-scan techniques, apparently decrease with the Cu²⁺ content. Intensity-dependent TA curves offer their carrier recombination rate constants (involving the mono-molecular (k₁), bi-molecular (k₂) and Auger recombination (k₃) rate constants). Herein, k₁ decreases with the Cu²⁺ content owing to the variance of Cu–Cl bonds in the x–y plane, but k₂ and k₃ show an opposite trend. The current–voltage test with strong light bias confirms that the monomolecular recombination is dominant in the operation of photo-detectors based on Cs₄Cu_xAg_2−2xSb₂Cl₁₂ NC films and the light-harvesting ability should be responsible for the photocurrent of the photo-detector. Our results provide a comprehensive insight into the optoelectronic properties of these double perovskite NCs.