Grain boundaries passivation of high efficiency and stable perovskite photodetector by polyoxometalate-based composite SiW₁₁@ZIF-8

Polyoxometalates (POMs) can enable energy level tuning to match perovskite layers. They are considered electronic bridges to modify perovskite and improve the performance of photovoltaic devices. Therefore, in the present work, we dispersed the vacancy POMs K₈[α-SiW₁₁O₃₉]·H₂O ({SiW₁₁}) in the metal-organic frameworks (MOFs) to modify the perovskite layer. {SiW₁₁} could adjust the energy level between the layers of the perovskite photodetector. Moreover, the hydrogen bonds formed between SiW₁₁@ZIF-8 and perovskite effectively passivated the grain boundaries (GBs) of the perovskite layer. X-ray diffraction spectroscopy (XRD) showed that the crystallinity of perovskite was significantly improved. In addition, scanning electron microscopy (SEM) images demonstrated that the average size of perovskite grains increased from 254.50 to 719.27 nm, proving the effective passivation of the GBs. Furthermore, a series of tests such as infrared spectroscopy (IR), N₂ adsorption/desorption isotherms, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) also proved that {SiW₁₁} could be successfully loaded into the pores of ZIF-8 through electrostatic interactions. The photocurrent of the SiW₁₁@ZIF-8 doped device reached 41.95 μA, about three times as high as that of the blank device (14.41 μA). Also, under unencapsulated conditions, it could still maintain more than 90% stability for nearly 700 h. This work demonstrates the potential application of POM@MOF-type composites in the field of perovskite photodetectors.