Wide-Bandgap CaSnO₃ Perovskite As an Efficient and Selective Deep-UV Absorber for Self-Powered and High-Performance p-i-n Photodetector

Abstract

Calcium stannate (CaSnO 3 ) is an inorganic perovskite material with an ultrawide bandgap (4.2−4.4 eV) that is associated with its unique structural characteristics. Owing to its remarkable optical and electric properties and high physical and chemical stability, it has recently drawn significant interest for various applications such as photocatalysts for the degradation of organic compounds and hydrogen production under UV radiation, gas sensors, and thermally stable capacitors. In this study, we demonstrate a self-powered deep-UV (DUV) p-i-n photodetector consisting of CaSnO 3 thin film as an efficient DUV absorber via a low-temperature solution process. The physical, optical, and electrical properties of the as-synthesized CaSnO 3 are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, ultraviolet−visible spectroscopy, photoluminescence spectroscopy, space charge limited current, and four-point probe measurements. As a key component in a pi-n DUV photodetector, the thickness of the CaSnO 3 absorber layer and operating bias are optimized to enhance charge carrier transport, light absorption, and signal-to-noise ratio. As a result, the optimized device shows a high performance at zero bias under 254 nm UV illumination: with a specific detectivity of 1.56 × 10 10 Jones, fast rise/fall time of 80/70 ms, and high 254:365 nm photocurrent rejection ratio of 5.5 along with a stable photoresponse during 100 continuous cycles initially as well as after 1 month of storage. Accordingly, this study suggests that a novel CaSnO 3 -based photodiode prepared via a solution process can be employed for many practical DUV-detection applications.

Ultrahigh Stability of Wearable Photodetector Using Zirconium Metal‐Organic Framework Enabling In Situ and Continuous Monitoring of Ultraviolet Radiation Risk

“…The dark current observed in the photodetector using ZrBDC thin film was three orders of magnitude lower than those using the absorber based on CaSnO 3 (in our previous study [ 11 ] ) and TFB/SnO 2 p‐n heterojunction (without ZrBDC in Figure S4a, Supporting Information). This is reasonable because the trap density of ZrBDC thin film was much lower (2.85 × 10 16 cm –3 derived from Figure S4b, Supporting Information) than those of CaSnO 3 (2.61 × 10 19 cm –3[ 11 ] ) and SnO 2 (3.17 × 10 16 cm –3[ 20 ] ). It was worth noting that a large number of the traps in absorber promotes the charge carrier injection from the Fermi level of conductive electrode to the vicinity states of photoactive layer, which is one of the major contributors to increase in dark current (depicted in Figure S4c, Supporting Information).…”

“…Notably, the device exhibited the ability to be operated at zero bias, where an on/off ratio reached 380 with a low dark current of 50 pA. The dark current observed in the photodetector using ZrBDC thin film was three orders of magnitude lower than those using the absorber based on CaSnO 3 (in our previous study [ 11 ] ) and TFB/SnO 2 p‐n heterojunction (without ZrBDC in Figure S4a, Supporting Information). This is reasonable because the trap density of ZrBDC thin film was much lower (2.85 × 10 16 cm –3 derived from Figure S4b, Supporting Information) than those of CaSnO 3 (2.61 × 10 19 cm –3[ 11 ] ) and SnO 2 (3.17 × 10 16 cm –3[ 20 ] ).…”

“…As observed in our previous studies, the performance of photodetectors strongly depends on the device structure. [ 11 ] In the present study, n‐type SnO 2 and p‐type poly(9,9‐dioctylfluorene‐alt‐N‐(4‐sec‐butylphenyl)‐diphenylamine) (TFB) were used as an electron transfer layer (ETL) and a hole transfer layer (HTL), respectively, for injection and transport of photocarriers generated in the absorber toward the electrodes owing to their high charge mobilities. Additionally, a thin branched‐polyethylenimine (PEI) film with high cationic charge density was introduced as a functionalized layer.…”

2D Ultrawide Bandgap Semiconductors: Odyssey and Challenges

“…[ 172–174 ] Very recently, 2D UWBG Dion–Jacobson phase perovskite oxides are remarkable due to their enhanced stability, structural tunability, fascinating optical, and electric properties. [ 144,175 ] Fang and co‐workers reported, for the first time, stable and nontoxic Sr 2 Nb 3 O 10 monolayer was successfully liquid exfoliated through an ion‐exchange approach from Dion–Jacobson‐phase bulk materials. [ 33 ] Subsequently, Other 2D UWBG perovskite oxides have been developed by Fang's group, such as Ca 2 Nb 3 O 10 , [ 35 ] Ca 2 Nb 3‐ x Ta x O 10 .…”

“…2D ultrawide bandgap Dion-Jacobson layered perovskite oxides could serve in prospective optoelectronic devices owing to their unique structure, physical properties, and reduced dimension. [35,62,119,144,173,175] Fang and co-worker first reported that 2D all-inorganic perovskite Sr 2 Nb 3 O 10 nanosheets with thickness of 1.8 nm were fabricated by liquid exfoliation. According to the ultraviolet-visible absorption spectrum, the Sr 2 Nb 3 O 10 nanosheets delivered negligible absorption over visible range and a sharp absorption edge at 300 nm, leading to an estimated of 3.9 eV by the Tauc plot.…”