Dual-sized carbon quantum dots enabling outstanding silicon-based photodetectors

Broadband and reliable photodetectors were in high demand due to their potential applications for optical communications, sensing and photoelectronic switches. Here, the facile in-situ formation of dual-sized carbon quantum dot (CQD) films featuring dense contact with silicon (Si) substrates that avoided the formation of interface oxide was demonstrated. The unique features of dual-size graded CQDs constituted the bottom layer of 10-nm CQDs functioning as the main light harvester and facilitating the heterojunction establishment with Si, while the top component of 6-nm CQDs at top featuring the electron blocking layer as well as hole extractor. Such heterostructures allowed the low dark current which was an order of magnitude less than monodispersed CQDs, and manifested the sound operation stability under systematic examinations including abrasion test, variations of temperature and environmental pH conditions and long-term switching test. In addition, the dependence of photocurrent on light intensity was fitted with power law relationship, showing the fairly identical characteristics by examining light illuminations of 850 nm, 580 nm, and 352 nm, respectively, which validated the wavelength-independent and compelling photodetection quality. These results represented a significant advancement in photodetector design with all-solution synthesis and pronounced high performances.