Interface engineering strategies towards Cs2AgBiBr6 single-crystalline photodetectors with good Ohmic contact behaviours

Abstract

Lead-free double perovskite materials have attracted much interest for optoelectronic applications due to their nontoxicity and high stability. In this work, centimetre-sized Cs₂AgBiBr₆ single crystals were successfully grown using methylammonium bromide (MABr) as the flux by a top-seeded solution growth (TSSG) method. The low-temperature crystal structure of Cs₂AgBiBr₆ single crystals was determined and refined. To investigate the interface problems between Cs₂AgBiBr₆ single crystals and electrodes, the optical band gap, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements were performed on Cs₂AgBiBr₆ single crystals. More importantly, we investigated the photodetectors based on Cs₂AgBiBr₆ single crystals with different contact electrodes (Au, Ag, and Al). It is found that a good Ohmic contact with Ag electrodes enables excellent photo-response behaviors. Furthermore, we studied the photodetectors based on Cs₂AgBiBr₆ single crystals using Ag electrodes under room and low temperature conditions, which underwent phase transition. Cs₂AgBiBr₆ single crystal photodetectors show clear differences at room and low temperatures, which is caused by the work function changes of Cs₂AgBiBr₆ single crystals induced by the reversible phase transition. These attractive properties may enable opportunities to apply emerging double perovskite single-crystalline materials for high-performance optoelectronic devices.