Photocurrent Quantum Efficiency Research Articles

High-Performance Broadband Self-Driven Photodetector Based on MoS2/Cs2CuBr4 Heterojunction.

Few-layer transition metal dichalcogenides and perovskites are both promising materials in high-performance optoelectronic devices. Here, we developed a self-driven photodetector by creating a heterojunction between few-layer MoS2 and lead-free perovskite Cs2CuBr4. The detector shows a unique property of very high sensitivity in a broad spectral range of 400 to 800 nm with response speed in a millisecond order. Current-voltage characteristics of the heterojunction device show rectifying behavior, in contrast to the ohmic behavior of the MoS2-based device. The rectifying behavior is attributed to the type II band alignment of the MoS2/Cs2CuBr4 heterojunction. The device shows a broadband (400 to 800 nm) photodetection with very high responsivity reaching up to 2.8 × 104 A/W and detectivity of 1.6 × 1011 Jones at a bias voltage of 3 V. The detector can also operate in self-bias mode with sufficient response. The photocurrent, photoresponsivity, detectivity, and external quantum efficiency of the device are found to be dependent on the illumination power density. The response time of the device is found to be ∼32 and ∼79 ms during the rise and fall of the photocurrent. The work proposes a MoS2/Cs2CuBr4 heterostructure to be a promising candidate for cost-effective, high-performance photodetector.

Broad band modulation of two-dimensional Mo1-x W x S2 by variational compositions

Precisely tuning bandgap enables tailored design of materials, which is of crucial importance for optoelectronic devices. Towards this end, ternary Mo1-x W x S2 monolayers with continually variational transition metal compositions are synthesized by precisely control of the precursors and growth temperatures in the chemical vapor deposition process, and thus to manipulate the bandgap of the monolayers. Energy dispersive x-ray spectroscopy demonstrates that the composition of the ternary Mo1-x W x S2 monolayers can be effectively modulated by the precursors and synthesizing temperatures. Frequency and intensity of the Raman and photoluminescent peaks of the Mo1-x W x S2 monolayers are continually modulated by the variational Mo and W compositions. The maximum of 0.148 eV bandgap modulation is achieved by modulating the transition metal compositions, which is highly consistent to the calculated 0.158 eV by first-principles theory. Photodetectors based on the Mo1-x W x S2 monolayers are fabricated and U-shape of photoresponse characteristics are demonstrated as x change from 0 to 1 under the same measurement conditions. The estimated photocurrent, photoresponsivity and external quantum efficiency show that the minimum values appear at the composition of x = 0.5, while the maximum values appear at x = 1. The results illustrate an excellent level of control on the band structure of two-dimensional ternary Mo1-x W x S2 by precisely control of the transition metal compositions.

Lewis acid catalysis of polydopamine electropolymerisation as a tool for shaping its morphology and electrochemical properties

Organic–inorganic semiconductor interfaces are of utmost importance in many photoelectrochemical applications, including water splitting and photodegradation of pollutants. The current work focuses on the fabrication and characterisation of transition metal-loaded polydopamine (PDA) electropolymerised on the surface of titania nanotubes. The structural studies via X-ray photoelectron spectroscopy and electron microscopy confirmed the catalytic effect of d-metal salts on the formation of the PDA layer during electropolymerisation. Cu and Ni loading leads to a significant enhancement of the visible absorption compared to that of the pristine PDA, also confirmed by the density functional theory calculations. Although the boost is greater for the thickest coatings, an excess amount of polymer suppresses the charge transfer and thus photocurrent generation. Synthesis in acidic conditions—optimal for photosensitisation—provides structures with a strong increase in the photocurrent quantum efficiency in the visible range, equal to 20% at 400 nm.Graphical

High photoresponse detectors based on Yb-doped monolayer WS2 nanosheets

The study of rare-earth (RE) doping in two-dimensional (2D) transition metal dichalcogenides (TMDCs) has become an important research focus to modulate bandgaps and carriers for production of the exotic properties. Herein, approximately 7 at% of Yb substitutionally doped monolayer WS2 nanosheets are prepared by in-situ chemical vapor deposition (CVD) technique. Highly enhanced optical and electrical properties are obtained: Three times enhancement in photoluminescent intensities and 5.6 nm of red-shifts in wavelength are observed from their peaks after chemical doping. First-principles calculations based on density functional theory (DFT) demonstrate a shrinked bandgap of Yb-doped monolayer WS2 at K-point in Brillouin zone compared with that of the pristine WS2 monolayer, and a broadened absorption and reflectivity spectra from visible to near-infrared region, which is in good agreement with the experimental results. Photodetectors based on Yb-doped monolayer WS2 nanosheets show far higher of mobility (17 times), photocurrent, photoresponsivity, and external quantum efficiency than those of the pristine WS2. The results prove a high effectiveness of RE doping in 2D materials for high-performance optoelectronic devices.

High‐Performance Self‐Assembled ZnO Nanowrinkle Network Structured Photodetectors

Herein, the effect of prebake temperature on the surface structure of zinc oxide (ZnO) nanowrinkle structures formed in a sol–gel growth process for UV photodetection is demonstrated. The sol–gel solutions are spin‐coated on glass and c‐plane sapphire substrates, and the resulting ZnO films are subjected to prebake and crystallization processes at 800 °C for an hour. In the sol–gel process, the prebake process is crucial in forming the nanowrinkle structure on the surface of the ZnO film. The maximum nanowrinkle structure of ZnO film is achieved at the prebake temperature of 150 °C. In addition to the formation of the optimized nanowrinkle structure, the UV response of the photodetector is further enhanced through the prebake temperature control. The nanowrinkle network structure significantly improves the optical absorbance and photoluminescence characteristics of the ZnO film, leading to high photocurrent, photoresponsivity, and external quantum efficiency for UV light. The results demonstrate the potential of sol–gel‐derived ZnO photodetectors with nanowrinkle network structures for UV sensing applications.

P‐7: Enhanced Visible Light Response of Amorphous InZnO Thin‐Film Transistors by Hydrogen Doping via Al2O3/SiO2 Gate Dielectric

Enhancement of visible light response in InZnO (IZO) thin‐film transistors (TFTs) by hydrogen doping via Al2O3/SiO2 dielectric layer is investigated. The IZO TFTs with Al2O3/SiO2 dielectric show better visible light detection performance due to the introduction of subgap states by hydrogen doping. The photocurrent, photoresponsivity, detectivity, and external quantum efficiency of the device to blue light are respectively improved from 4.94 × 10−7 A to 1.97 × 10−6 A, 4.93 A/W to 19.71 A/W, 2.70 × 1012 Jone to 5.77×1012 Jone, and 13.60 to 54.32 after hydrogen doping. The persistent photoconductivity effect is also eliminated by applying a positive gate pulse voltage.

Engineering the physical properties of CdS thin films through incorporation of Fe dopant for photodetector applications

Pure CdS and 1, 2, 3, 4, and 5 wt% Fe-doped CdS thin films have been fabricated on glass substrates at a coating temperature of 450 °C by a simple and economical spray-pyrolysis technique. The prepared samples have been characterized by various analytical techniques to assess their crystalline, morphological, optical, and photo-sensing properties. X-ray diffraction (XRD) analysis has revealed the presence of the hexagonal wurtzite phase of CdS, with (002) as the predominant plane. With the incorporation of the Fe dopant into CdS, the peak of the predominant plane (002) increases, suggesting an increase in the crystallinity of the samples. The CdS:Fe4% sample showed the largest crystallite size of 49 nm. The morphologies of the prepared thin films reveal uniform clusters of very fine nanoparticles, with the incorporation of Fe ions in CdS improving the particle size and porosity, which is beneficial for light harvesting. UV/Vis studies have indicated an improvement in the optical absorption of the CdS:Fe4% sample, with a reduction in the band gap to 2.29 eV. Photoluminescence (PL) spectra feature broad emission peaks at around 460, 535, and 640 nm, the intensities of which increase with the incorporation of the Fe dopant, suggesting improved radiative recombination of excitons and defect sites, such as S vacancies and Cd vacancies. Photo-sensing studies of the fabricated devices showed the highest photocurrent (28 μA), responsivity (5.59 × 10−1 AW−1), detectivity (9.05 × 1010 Jones), and external quantum efficiency (180%), as well as the shortest response time (0.1 s) and recovery time (0.2 s), for the CdS:Fe4% photodetector, suggesting that this sample is best suited for commercial application in photodetectors.

Fabrication and characterization of silver polycrystalline photocathode

Silver is considered the most noble metal after gold, which makes it a potential candidate for the metallic photocathode. In this article, we report on the fabrication of a polycrystalline silver photocathode by using a physical vapor deposition (PVD) technique. For the first time, silver photocathodes in both the reflection and transmission modes were fabricated on a super quartz (JGS1) substrate and characterized. The polycrystalline nature of the fabricated sample was confirmed by X-ray diffraction (XRD) analysis. The work function of the fabricated photocathode was measured at around 4.73 eV using photoemission yield spectroscopy in the air (PYSA). Photocurrent measurement and quantum efficiency (Q.E.) calculations were performed using a picoammeter and a 250 nm high power ultraviolet (UV) LED source. Silver photocathode yielded a Q.E. of (8.77±0.90)×10−6 in reflection mode, and (1.20±0.12)×10−6 in transmission mode. After being exposed to air for up to 72 h, no sign of degradation in its photocurrent/Q.E. was observed. The silver photocathode thickness was estimated to be (138 ± 5) nm for the reflection mode and (35 ± 1) nm for the transmission mode. The developed photocathode will be ultimately used for the study of the proposed novel photodetector concept called silicon photomultiplier tube (SiPMT).

Multiple exciton generation in tin–lead halide perovskite nanocrystals for photocurrent quantum efficiency enhancement

Multiple exciton generation (MEG), the generation of multiple electron–hole pairs from a single high-energy photon, can enhance the photoconversion efficiency in several technologies including photovoltaics, photon detection and solar-fuel production1,2,3,4,5,6. However, low efficiency, high photon-energy threshold and fast Auger recombination impede its practical application1,7. Here we achieve enhanced MEG with an efficiency of up to 87% and photon-energy threshold of two times the bandgap in highly stable, weakly confined formamidinium tin–lead iodide perovskite nanocrystals (FAPb1–xSnxI3 NCs; x ≤ 0.11). Importantly, an MEG-driven increment in the internal photocurrent quantum efficiency exceeding 100% with a low threshold is observed in such NC-sensitized photoconductors under ultraviolet-light illumination. The MEG enhancement mechanism is found to be mediated by the slower cooling and reduced trapping of hot carriers above the MEG threshold after the partial substitution of Pb by Sn. Our findings corroborate the potential importance of narrow-bandgap perovskite NCs for the development of optoelectronics that could benefit from MEG.

Synthesis, characterization and photo-detection parameters of (Sb0.05In0.95)Se crystals

The antimony doped indium selenide crystals have been grown using Direct Vapour Transport (DVT) technique. The compositional, morphological, structural and photoconductive properties of (Sb0.05In0.95)Se crystal has been characterized by EDAX, SEM, XRD and I-V measurement analysis respectively. SEM image shows that (Sb0.05In0.95)Se crystal has layer by layer growth. The photo-current of (Sb0.05In0.95)Se crystal was measured as a function of various illumination intensity of 50, 75, 100, and 125 mW/cm2. The photo-response parameters: photo-current, responsivity, specific detectivity, and external quantum efficiency EQE (%) have been estimated. The photo current at the termination of illumination (I0), probability of escape of an electron from the trap per second (p) and trap depth (Et) have been studied and determined by the growth decay curve. It depends upon illumination intensity of incident light source. These characteristics makes (Sb0.05In0.95)Se crystal suitable candidate for efficient photo-electric devices.

An insight in photocurrent generation mechanism on Cu2O quantum dot sensitized Cu/p-CuI photo-electrochemical cell and efficient H2 generation at Cu/p-CuI/Cu2O electrolyte interface

p-CuI (band gap ≈ 3.1 eV) is sensitised with quantum dots (QDs) of Cu2O (band gap ≈ 2.0 eV) as a novel hybrid strategy to make photoelectrochemical cells. In which, p-CuI thin film was deposited by immersing a cleaned copper sheet into a solution containing I2 (10−2 M), KI (0.1 M), CuSO4 (10−3 M) to make Cu/p-CuI photoelectrodes. To fabricate Cu/p-CuI/Cu2O photoelectrodes, Cu/p-CuI photoelectrodes were boiled in a CuSO4 (10−2 M) solution at different time intervals. When gradually increases the boiling time until 5 min, the size of the p-CuI microcrystals decreases with the formation of Cu2O QDs on p-CuI microcrystals. When the boiling period exceeds 5 mins, Cu2O QDs convert gradually into micro-crystals and covering p-CuI thin film. Variations in the photocurrent quantum efficiency (Φ%) with the Cu2O amount fabricated on p-CuI thin layer were monitored. The photophysical and photochemical processes associated at Cu/p-CuI/Cu2O-electrolyte interface are presented to delineate the sensitisation of p-CuI wide band gap semiconductor with Cu2O QDs produced. Our recent explanation on the kinetics of the photocurrent generation by dye sensitised solar cells using CAN’s model equation Φ = AD0 – BD02, was used to describe the QD sensitisation of p-CuI by Cu2O QDs. It was experimentally confirmed that CAN’s constant ‘A’ relates with the photocurrent generation processes and the CAN’s constant ‘B’ associated with the processes in suppression of photocurrent generation. Material characterisation from Scanning Electron Microscopy (SEM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), UV absorption, photocurrent action spectra, and photoelectrochemical (PEC) measurements through I-V characteristics are presented to confirm the formation of Cu/CuI/Cu2O electrodes. A remarkable H2 generation was noticed in the presence of 0.025 M Na2SO4 solution, from the QDs sensitised photogenerated electrons at Cu/p-CuI/Cu2O-electrolyte interface. The mechanism of H2 generation is confirmed with the energy band positions of p-CuI and Cu2O QDs under visible light irradiation. Different H2 profiles are presented in detail with the size of QDs fabricated on p-CuI.

Eco-Friendly AgBiS2 Nanocrystal/ZnO Nanowire Heterojunction Solar Cells with Enhanced Carrier Collection Efficiency.

AgBiS2 nanocrystals (NCs) are nontoxic, lead-free, and near-infrared absorbing materials. Eco-friendly solar cells were constructed using interdigitated layers of ZnO nanowires (NWs) and AgBiS2 NCs, with the aim of elongating the otherwise short carrier diffusion length of the AgBiS2 NC assembly. AgBiS2 NCs were uniformly infiltrated into the ZnO NW layers using a low-cost and easily scalable dip coating method. The resulting ZnO NW/AgBiS2 NC interdigitated structures provided efficient carrier pathways in constructed nanowire solar cells (NWSCs), composed of a transparent electrode/ZnO NW/AgBiS2 NC interdigitated layer/P3HT hole transport layer/Au. The photocurrent external quantum efficiency (EQE) in the visible to near-infrared regions was enhanced compared to those of the control solar cells made with ZnO/AgBiS2 tandem layered structures. The maximum EQE for the NWSCs reached 82% in the visible region, which is higher than the EQE values previously reported for solar cells fabricated with ZnO/AgBiS2 NCs. Air stability tests on unsealed NWSCs demonstrated that 90% or more of the initial power conversion efficiency was maintained even after 6 months.

All-organic thin film flexible photodetector based on C60 modified PEDOT:PSS

In organic electronics, the use of self-assembled monolayer dielectric functional groups is considered an effective surface modification strategy that can significantly improve device performance. A flexible polymer (PEDOT:PSS) photodetector on the substrate polyimide with broadband response (450 nm ∼ 980 nm) and high response (0.56 A W−1) is reported, which is superimposed on the surface by small molecule (C60) thermal evaporation. In addition, the planeness of the organic semiconductor and the overall performance of the organic thin film photodetector can be improved significantly by using a small molecule modified polymer thin film; the photocurrent, Ri and external quantum efficiency were all increased by more than 10%. The response time of the device reached an astonishing 5.87 ms, much faster than that of similar devices. The response of the small molecule modified organic device is improved by an order of magnitude, which provides a guarantee for better application of organic thin films in circuits. Moreover, the device has a strong flexible stability performance, which can meet the requirements of flexible stability for future photoelectric devices.

Enhanced Surface Charge Separation Induced by Ag Nanoparticles on WO3 Photoanode for Photoelectrochemical Water Splitting

Monoclinic WO3 is considered to be a promising photoanode due to high theoretical photocurrent density and quantum efficiency. However, the practical photoelectrochemical (PEC) performance is consi...

Finding the Energy Gap of Ga1 –xInxAs p–n Junctions on a Metamorphic Buffer from the Photocurrent Spectrum

A relationship has been established between the energy gap width of GaInAs p–n homojunctions and the saturation current. For this purpose, a method was suggested and substantiated for determining the energy gap width of a p–n junction from the spectrum of the photocurrent quantum efficiency. The method was applied to Ga1 –xInxAs p–n junctions grown by metal-organic vapor-phase epitaxy on metamorphic buffers. The difference between the energy gap width determined by using the suggested method and that found from the peak of the electroluminescence spectrum did not exceed 3 meV. It was found that the saturation current exponentially depends on the energy gap width, and this dependence is characterized by a current invariant.

Harnessing Exciton-Exciton Annihilation in Two-Dimensional Semiconductors.

Strong many-body interactions in two-dimensional (2D) semiconductors give rise to efficient exciton-exciton annihilation (EEA). This process is expected to result in the generation of unbound high energy carriers. Here, we report an unconventional photoresponse of van der Waals heterostructure devices resulting from efficient EEA. Our heterostructures, which consist of monolayer transition metal dichalcogenide (TMD), hexagonal boron nitride (hBN), and few-layer graphene, exhibit photocurrent when photoexcited carriers possess sufficient energy to overcome the high energy barrier of hBN. Interestingly, we find that the device exhibits moderate photocurrent quantum efficiency even when the semiconducting TMD layer is excited at its ground exciton resonance despite the high exciton binding energy and large transport barrier. Using ab initio calculations, we show that EEA yields highly energetic electrons and holes with unevenly distributed energies depending on the scattering condition. Our findings highlight the dominant role of EEA in determining the photoresponse of 2D semiconductor optoelectronic devices.

Effective p-type photocurrent sensitization of n-Bi2O3 with p-CuBi2O4 and p-CuO: Z-scheme photoelectrochemical system

Nanostructured n-Bi2O3/p-CuBi2O4/p-CuO photocathodes with incident photon-to-current conversion efficiency IPCEmax = 70% (λ = 400 nm) have been prepared using electrochemical and chemical methods. Platelet-like BiOI nanocrystals electrochemically deposited on FTO substrate were used as precursors. CuI nanoparticles were deposited on the BiOI surface by successive ionic layer adsorption and reaction technique. Oxidative heat treatment of BiOI/CuI heterostructure in air leads to the formation of the Bi2O3/CuBi2O4/CuO composite. Binary oxide was formed as a result of solid-state interaction between bismuth and copper oxides at their interface. Spectral sensitization of wide-gap n-Bi2O3 (band gap Eg = 2.80 eV) with narrow-gap p-CuBi2O4 (Eg = 1.80 eV) and p-CuO (Eg = 1.45 eV) extends spectral sensitivity range up to 800 nm by Z-scheme implementation: cathodic photocurrent is associated with the transition of photoelectrons from p-CuBi2O4 and p-CuO to the solution, while photoholes recombine with electrons of n-Bi2O3 conduction band. High quantum efficiency of photocurrent was achieved due to band-edge correlation in a three-component oxide heterostructure, combined with an internal electric field in p-CuBi2O4 and effective photon absorption by two narrow-band-gap p-CuBi2O4 and p-CuO semiconductors.

2D Modeling of Solar Cell p-n Radial Junction: Study of Photocurrent Density and Quantum Efficiency in Static Mode under Monochromatic Illumination

A theoretical study of a polysilicon solar cell with a radial junction in static regime under monochromatic illumination is presented in this paper. The junction radial solar cell geometry is illustrated and described. The carriers’ diffusion equation is established and solved under quasi-neutral base assumption with boundaries conditions and Bessel equations. New analytical expressions of electrons and holes photocurrent density and quantum efficiency are found. The wavelength and structural parameters (base radius, base thickness and wavelength) influences on photocurrent density and quantum efficiency are carried out and examined.

Efficient Nonfullerene Organic Solar Cells with Small Driving Forces for Both Hole and Electron Transfer.

State-of-the-art organic solar cells (OSCs) typically suffer from large voltage loss (Vloss ) compared to their inorganic and perovskite counterparts. There are some successful attempts to reduce the Vloss by decreasing the energy offsets between the donor and acceptor materials, and the OSC community has demonstrated efficient systems with either small highest occupied molecular orbital (HOMO) offset or negligible lowest unoccupied molecular orbital (LUMO) offset between donors and acceptors. However, efficient OSCs based on a donor/acceptor system with both small HOMO and LUMO offsets have not been demonstrated simultaneously. In this work, an efficient nonfullerene OSC is reported based on a donor polymer named PffBT2T-TT and a small-molecular acceptor (O-IDTBR), which have identical bandgaps and close energy levels. The Fourier-transform photocurrent spectroscopy external quantum efficiency (FTPS-EQE) spectrum of the blend overlaps with those of neat PffBT2T-TT and O-IDTBR, indicating the small driving forces for both hole and electron transfer. Meanwhile, the OSCs exhibit a high electroluminescence quantum efficiency (EQEEL ) of ≈1 × 10-4 , which leads to a significantly minimized nonradiative Vloss of 0.24 V. Despite the small driving forces and a low Vloss , a maximum EQE of 67% and a high power conversion efficiency of 10.4% can still be achieved.

High-performance Core/Shell InGaN/GaN Radial Multi-quantum-well Nanowire Solar Cells Non-catalytically Grown on Si Wafers

We report photovoltaic properties of solar cells made of core/shell InGaN/GaN multi quantum wells (MQWs)-nanowire (NW) arrays, vertically-grown through oxide-template hole patterns from n-GaN thin films on n-type Si wafers. Detailed structural properties are analyzed for two types of the solar cells containing defect-free or defective active layer (MQWs) by high-resolution transmission electron microscopy. Photocurrent and external quantum efficiency are greatly enhanced in the defect-free solar cells due to better charge collection/transport. Maximum power conversion efficiency (PCE) of ~ 4.22%, highest ever known for the similar structures, is achieved with ~ 1.11 V open-circuit voltage, ~ 6.80 mA/cm2 short-circuit current density, and ~ 0.56 fill factor in the defect-free solar cells. These results suggest that the well-defined active layer in InGaN/GaN MQWs-NWs solar cells is crucial for enhancing their PCE and further explain why the PCE of the solar cells employing similar structures in the previous reports were comparatively low.