Ultrafast and broadband photodetectors based on a perovskite/organic bulk heterojunction for large-dynamic-range imaging

Organic-inorganic hybrid perovskite(OIHP)photodetectors that simultaneously achieve an ultrafast response and high sensitivity in the near-infrared(NIR)region are prerequisites for expanding current monitoring,imaging,and optical communication capbilities.Herein,we demonstrate photodetectors constructed by OIHP and an organic bulk heterojunction(BHJ)consisting of a low-bandgap nonfullerene and polymer,which achieve broadband response spectra up to 1μm with a highest external quantum efficiency of approximately 54%at 850 nm,an ultrafast response speed of 5.6 ns and a linear dynamic range(LDR)of 191 dB.High sensitivity,ultrafast speed and a large LDR are preeminent prerequisites for the practical application of photodetectors.Encouragingly,due to the high-dynamicrange imaging capacity,high-quality visible-NIR actual imaging is achieved by employing the OIHP photodetectors.We believe that state-of-the-art OIHP photodetectors can accelerate the translation of solution-processed photodetector applications from the laboratory to the imaging market.

Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors.However,for most phototransistors,the photoresponse characteristics are modulated with an electrical gate or a static field.In this paper,we demonstrate a graphene/C_(60)/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation.By exploiting the power-dependent multiple states of the photocurrent,remarkable logical photocurrent switching under infrared light modulation occurs in a thick C_(60) layer(11 nm)device,which implies competition of the photogenerated carriers between graphene/C_(60) and C_(60)/pentacene.Meanwhile,we observe a complete positive-negative alternating process under continuous 405 nm irradiation.Furthermore,infrared light modulation of a thin C_(60)(5 nm)device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W,and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C_(60) devices.In addition,the tuneable bandwidth of the infrared response from 10 to 3×10^(3) Hz under visible light modulation is explored.Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.

Linking polynomials of virtual string links

In this paper, we define two polynomial invariants for virtual string links. One can be defined only on 2-component virtual string links. The other is defined on virtual string links with arbitrary components.Both invariants can distinguish virtual string links from their mirror images. In addition, we also show that these two invariants are link homotopic invariants. In the end, we give some interesting examples to show that the two invariants are different.