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Field effect transistors have shown promising performance as terahertz (THz) detectors over the past few decades. Recently, a quantum phenomenon, the in-plane photoelectric effect, was discovered as a novel detection mechanism in gated two-dimensional electron gases (2DEGs), and devices based on this effect, photoelectric tunable-step (PETS) THz detectors, have been proposed as sensitive THz detectors. Here, we demonstrate a PETS THz detector based on GaAs/AlGaAs heterojunction using a dipole antenna. We investigate the dependence of the in-plane photoelectric effect on parameters including the dimensions and the operating temperature of the device. Two figures of merit within the 2DEG, the maximum electric field and the radiation-induced ac-potential difference, are simulated to determine the optimal design of the PETS detector antenna. We identify the optimal antenna gap size, metal thickness, and 2DEG depth, and demonstrate the first PETS detector with a symmetric dipole antenna, which shows high-speed detection of 1.9 THz radiation with a strong photoresponse. Our findings deepen the understanding of the in-plane photoelectric effect and provide a universal guidance for the design of future PETS THz detectors.

We study the optical response of a suspended, monolayer graphene field-effect transistor structure in magnetic fields of up to 9 T (quantum Hall regime). With an illumination power of only 3 W, we measure a photocurrent of up to 400 nA (without an applied bias) corresponding to a photo-responsivity of 0.13 A W−1, which we believe to be one of the highest values ever measured in single-layer graphene. We discuss possible mechanisms for generating this strong photo-response (17 electron-hole pairs per 100 incident photons). Based on our experimental findings, we believe that the most likely scenario is a ballistic two-stage process including carrier multiplication via Auger-type inelastic Coulomb scattering at the graphene edge.

The photoelectric effects on the instability of the current-driven dust ion-acoustic (DIA) waves in a collisional and streaming dusty plasmas are theoretically investigated using fluid model with dust charge fluctuation considering dust grains as negatively charged. It is found that the photoelectric effects through dust charge fluctuation give the growth of the DIA waves beside the damping effects of collision and streaming of the plasma species. Growth rate of the DIA waves are numerically investigated using the values of appropriate plasma parameters.

The general review of cross section formulas for the photoelectric effect, Compton scattering, pair and triplet production is presented in the intermediate and high photon energy spectrum for carbon (Z = 6). Using the classical Gaussian regression method, the empirical correction functions for the theoretical cross section formulas are calculated based on the existing experimental data. The simple formulas can be used to calculate the cross sections of four main radiation effects with a good accuracy. The proposed formulas are enough for practical calculations in the excel spreadsheet in e.g. radiation protection applications or radiation shields designing.

Inverted planar perovskite solar cells offer opportunities for a simplified device structure compared with conventional mesoporous titanium oxide interlayers. However, their lower open-circuit voltages result in lower power conversion efficiencies. Using mixed-cation lead mixed-halide perovskite and a solution-processed secondary growth method, Luo et al. created a surface region in the perovskite film that inhibited nonradiative charge-carrier recombination. This kind of solar cell had comparable performance to that of conventional cells. Science , this issue p. 1442 High open-circuit voltages were achieved for planar perovskite solar cells by creating a graded junction. The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages ( V oc ). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in V oc by up to 100 millivolts. We achieved a high V oc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

The photocurrent generation in photovoltaics relies essentially on the interface of p-n junction or Schottky barrier with the photoelectric efficiency constrained by the Shockley-Queisser limit. The recent progress has shown a promising route to surpass this limit via the bulk photovoltaic effect for crystals without inversion symmetry. Here we report the bulk photovoltaic effect in two-dimensional ferroelectric CuInP 2 S 6 with enhanced photocurrent density by two orders of magnitude higher than conventional bulk ferroelectric perovskite oxides. The bulk photovoltaic effect is inherently associated to the room-temperature polar ordering in two-dimensional CuInP 2 S 6 . We also demonstrate a crossover from two-dimensional to three-dimensional bulk photovoltaic effect with the observation of a dramatic decrease in photocurrent density when the thickness of the two-dimensional material exceeds the free path length at around 40 nm. This work spotlights the potential application of ultrathin two-dimensional ferroelectric materials for the third-generation photovoltaic cells. While magnetism, hyperferroelectricity, and topological phases in the two-dimensional limit have been widely explored, the direct experimental study on bulk photovoltaic effect in 2D materials remains unimplemented. Here, the authors find bulk photovoltaic effect in 2D ferroelectric CuInP 2 S 6 .

Spectrometers with ever-smaller footprints are sought after for a wide range of applications in which minimized size and weight are paramount, including emerging in situ characterization techniques. We report on an ultracompact microspectrometer design based on a single compositionally engineered nanowire. This platform is independent of the complex optical components or cavities that tend to constrain further miniaturization of current systems. We show that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along the length of the nanowire. Our devices are capable of accurate, visible-range monochromatic and broadband light reconstruction, as well as spectral imaging from centimeter-scale focal planes down to lensless, single-cell–scale in situ mapping.

For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability. A systematic design of light-absorbing molecules is challenging for them to satisfy multiple key requirements for efficient solar cell application. Here, the authors optimize halogen substitution position in terminal groups of acceptors for realizing ternary cells with efficiency approaching 20%.

Conventional imaging and recognition systems require an extensive amount of data storage, pre-processing, and chip-to-chip communications as well as aberration-proof light focusing with multiple lenses for recognizing an object from massive optical inputs. This is because separate chips ( i . e ., flat image sensor array, memory device, and CPU) in conjunction with complicated optics should capture, store, and process massive image information independently. In contrast, human vision employs a highly efficient imaging and recognition process. Here, inspired by the human visual recognition system, we present a novel imaging device for efficient image acquisition and data pre-processing by conferring the neuromorphic data processing function on a curved image sensor array. The curved neuromorphic image sensor array is based on a heterostructure of MoS 2 and poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane). The curved neuromorphic image sensor array features photon-triggered synaptic plasticity owing to its quasi-linear time-dependent photocurrent generation and prolonged photocurrent decay, originated from charge trapping in the MoS 2 -organic vertical stack. The curved neuromorphic image sensor array integrated with a plano-convex lens derives a pre-processed image from a set of noisy optical inputs without redundant data storage, processing, and communications as well as without complex optics. The proposed imaging device can substantially improve efficiency of the image acquisition and recognition process, a step forward to the next generation machine vision. Designing efficient bio-inspired visual recognition system remains a challenge. Here the authors present a curved neuromorphic image sensor array based on a heterostructure of MoS2 and pV3D3 integrated with a plano-convex lens for efficient image acquisition and data pre-processing.

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. Here we find that in a class of Weyl semimetals (for example, SrSi 2 ) and three-dimensional Rashba materials (for example, doped Te) without inversion and mirror symmetries, the injection contribution to the CPGE trace is effectively quantized in terms of the fundamental constants e , h , c and with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques. Photocurrent switches depend on circular polarization of the incident light. Here, De Juan et al . report a quantized circular photogalvanic effect as a measure of the topological charge of Weyl points in a class of Weyl semimetals and three-dimensional Rashba materials.