Shallow Trap States Mediated Ultrafast InterfacialCharge Transfer in Ag/Bi-Codoped CsPbBr₃ Nanocrystals forHigh-Responsivity Photodetector Applications

Heterovalent metal ion doping into lead halide perovskite nanocrystals [perovskite NCs (PNCs)] has garnered great attention over the past few years due to the emergence of their fascinating optoelectronic properties. In this work, Ag/Bi-codoped CsPbBr₃ nanocrystals (NCs) are synthesized by partial substitution of Pb²⁺ via the hot injection method. The obtained results reveal that the control amount of Ag⁺ and Bi³⁺ codoping can contribute to individual characteristics of the optoelectronic properties, which creates shallow trap states close to the valence band and conduction band levels. Fabricated vertical hole-transport-layer-free (HTL-free) photodetectors with Ag/Bi-codoped CsPbBr₃ NCs exhibit a substantial photoresponse with photocurrent to the dark current ratio 4.15 × 10⁶, indicating efficient electron–hole pair generation and collection into respective electrodes. Furthermore, there is a remarkable enhancement of ∼900%, 600%, and 650% in photocurrent, responsivity, and detectivity, respectively, compared to the pristine PNC photodetector. Additionally, femtosecond transient absorption spectroscopy (fs-TAS) data revealed a faster charge transfer at the Ag/Bi-codoped PNCs/TiO₂ interfaces compared to the pristine CsPbBr₃/TiO₂ interfaces. This work presents an innovative codoping strategy to improve the optoelectronic properties of halide PNCs, paving the way for various futuristic optoelectronic devices.