Solution-grown BiI/BiI3 van der Waals heterostructures for sensitive X-ray detection.

X-ray detectors must be operated at minimal doses to reduce radiation health risks during X-ray security examination or medical inspection, therefore requiring high sensitivity and low detection limits. Although organolead trihalide perovskites have rapidly emerged as promising candidates for X-ray detection due to their low cost and remarkable performance, these materials threaten the safety of the human body and environment due to the presence of lead. Here we present the realization of highly sensitive X-ray detectors based on an environmentally friendly solution-grown thick BiI/BiI3/BiI (BixIy) van der Waals heterostructure. The devices exhibit anisotropic X-ray detection response with a sensitivity up to 4.3 × 104 µC Gy-1 cm-2 and a detection limit as low as 34 nGy s-1. At the same time, our BixIy detectors demonstrate high environmental and hard radiation stabilities. Our work motivates the search for new van der Waals heterostructure classes to realize high-performance X-ray detectors and other optoelectronic devices without employing toxic elements.

Infrared photodetectors based on CVD-grown graphene and PbS quantum dots with ultrahigh responsivity.

Infrared photodetectors based on single-layer CVD-grown graphene and PbS quantum dots, which are fabricated by solution processing, show ultrahigh responsivities of up to 10(7) A/W under infrared light illumination. The devices fabricated on flexible plastic substrates have excellent bending stability. The photoresponse is attributed to the field-effect doping in graphene films induced by negative charges generated in the quantum dots.

The application of highly doped single-layer graphene as the top electrodes of semitransparent organic solar cells.

A single-layer graphene film with high conductance and transparency was realized by effective chemical doping. The conductance of single-layer graphene was increased for more than 400% when it was doped with Au nanoparticles and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid). Then semitransparent organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with single-layer graphene and indium tin oxide (ITO) as the top and bottom electrodes, respectively. The performance of the devices was optimized by tuning the active layer thickness and doping the single-layer graphene electrodes. The maximum efficiency of 2.7% was observed in the devices with the area of 20 mm(2) illuminated from graphene electrode under the AM1.5 solar simulator. It is notable that all of the devices showed higher efficiency from the graphene than ITO side, which was attributed to the better transmittance of the graphene electrodes. In addition, the influence of the active area of the organic solar cell on its photovoltaic performance was studied. We found that, when the active areas increased from 6 to 50 mm(2), the power conversion efficiencies decreased from 3% to 2.3% because of the increased series resistances and the decreased edge effect of the devices.

Metallo-dielectric photonic crystals for surface-enhanced Raman scattering.

Metallo-dielectric photonic crystals (MDPCs) are used as ultrasensitive molecular detectors for concentrations down to picomolar level based on surface-enhanced Raman spectroscopy (SERS). Calculations show that the amorphous silicon photonic crystals (a-Si PCs) embedded in multiple metallo-dielectric (MD) units can significantly increase the electromagnetic fields at the air-dielectric interface, leading to remarkable Raman enhancement. Corresponding experiments show the multiple MDPC structures can serve as an ultrasensitive SERS substrate with excellent reproducibility and stability, capable of quantitative analysis down to 10 pM level. The MDPC structure can be generalized to other applications, such as plasmonic devices, ultrasensitive sensors, and nanophotonic systems.