Photodetectors based on reduced graphene oxide (rGO) have attracted much attention owing to their simple and low‐cost fabrication process. However, the aggregation and defects of rGO flakes still ...limit the performance of rGO photodetectors. Controlling the composition of rGO has become a vital factor for its prospective applications. For example, the interconnection between rGO and polymers for modified morphologies of rGO films leads to an enhanced performance of devices. In this work, a practical approach to engineer surface uniformity and enhance the performance of a photodetector by modifying the rGO film with hydrophilic polymers poly(vinyl alcohol) (PVA) is reported. Compared with the rGO photodetector, the on/off ratio for the PVA/rGO photodetector shows 3.5 times improvement, and the detectivity shows 53% enhancement even when the photodetector is operated at a low bias of 0.3 V. This study provides an effective route to realize PVA/rGO photodetectors with a low‐power operation which shows promising opportunities for the future development of green systems.
A practical approach to enhance the performance of a reduced graphene oxide (rGO) photodetector by modifying the rGO film with poly(vinyl alcohol) (PVA) is reported. Compared with the rGO photodetector, the on/off ratio for the PVA/rGO photodetector shows 3.5 times improvement, and the detectivity shows 53% enhancement at a low operating bias of 0.3 V.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
By employing graphene quantum dots (GQDs), we have achieved a high efficiency of 16.55% in n-type Si heterojunction solar cells. The efficiency enhancement is based on the photon downconversion ...phenomenon of GQDs to make more photons absorbed in the depletion region for effective carrier separation, leading to the enhanced photovoltaic effect. The short circuit current and the fill factor are increased from 35.31 to 37.47 mA/cm2 and 70.29% to 72.51%, respectively. The work demonstrated here holds the promise for incorporating graphene-based materials in commercially available solar devices for developing ultrahigh efficiency photovoltaic cells in the future.
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Low‐dimensional devices with different photoconductive effects attract much attention in optoelectronics. In this work, negative photoconductivity (NPC) monolayer graphene photodetectors are ...fabricated by chemical vapor deposition (CVD), and a positive photoconductivity (PPC) photodetector is realized by decorating perovskite FAPbI3 quantum dots prepared by a simple and cost‐effective non‐polar solvent synthesis method on a graphene surface. The graphene‐based photodetector exhibits an NPC characteristic, which is attributed to the absorption and desorption of water molecules on the graphene surface. The responsivity of the photodetector with an NPC characteristic is −0.86 A W−1 under intense ultraviolet light irradiation, and the detectivity is −2.45 × 109 Jones. The FAPbI3 quantum dots/graphene photodetector with a PPC feature has a responsivity of 8.03 A W−1 and a detectivity of 1.89 × 1010 Jones under the irradiation of ultraviolet light of 365 nm and 55.3 mW cm−2 intensity. Due to the intense light absorption of perovskite combined with the extremely high mobility of graphene, photodetectors have high exciton separation and photocurrents when the devices are irradiated by ultraviolet light. Individual photodetectors are successfully created with NPC and PPC effects; the critical analysis for the different photoconductive mechanisms is provided, which will benefit the development of future multifunctional systems.
Negative photoconductivity monolayer graphene photodetectors are fabricated by chemical vapor deposition, and positive photoconductivity photodetectors are realized by perovskite FAPbI3 quantum dots with a simple and cost‐effective non‐polar solvent synthesis method on the graphene surface. The combination of photodetectors with negative photoconductivity and positive photoconductivity effects can be simultaneously applied on a chip that benefits future intelligent Internet of Things systems.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Thin Copper (Cu) films (15 nm) are deposited on different 2D material surfaces through e-beam deposition. With the assist of van der Waals epitaxy growth mode on 2D material surfaces, preferential ...planar growth is observed for Cu films on both MoS
and WSe
surfaces at room temperature, which will induce a polycrystalline and continuous Cu film formation. Relative low resistivity values 6.07 (MoS
) and 6.66 (WSe
) μΩ-cm are observed for the thin Cu films. At higher growth temperature 200 °C, Cu diffusion into the MoS
layers is observed while the non-sulfur 2D material WSe
can prevent Cu diffusion at the same growth temperature. By further increasing the deposition rates, a record-low resistivity value 4.62 μΩ-cm for thin Cu films is observed for the sample grown on the WSe
surface. The low resistivity values and the continuous Cu films suggest a good wettability of Cu films on 2D material surfaces. The thin body nature, the capability to prevent Cu diffusion and the unique van der Waals epitaxy growth mode of 2D materials will make non-sulfur 2D materials such as WSe
a promising candidate to replace the liner/barrier stack in interconnects with reducing linewidths.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A highly efficient electron transport layer (ETL) is an essential constituent for good performance and stability in planar perovskite solar cells. Among n-type metal oxide materials, zinc oxide (ZnO) ...is a promising candidate for an electron transport layer due to its relatively high electron mobility, high transparency, and versatile nanostructures. However, it was found that several disadvantages could occur at the ZnO/perovskite interface, such as decomposition of CH3NH3PbI3 and poorly aligned energy levels. To overcome these issues, we present a design based on staircase band alignment of a low-temperature solution-processed ZnO/Al-doped ZnO (AZO) bilayer thin film as electron transport layers in planar perovskite solar cells. Experimental results revealed that the power conversion efficiency (PCE) of perovskite solar cells was significantly increased from 12.3% to 16.1% by employing the AZO thin film as the buffer layer. Meanwhile, the short-circuit current density (J sc), open-circuit voltage (V oc), and fill factor (FF) were improved to 20.6 mA/cm2, 1.09 V, and 71.6%, respectively. The enhancement in performance is attributed to the modified interface in the ETL with staircase band alignment of ZnO/AZO/CH3NH3PbI3, which allows more efficient extraction of photogenerated electrons in the CH3NH3PbI3 active layer. Our studies demonstrated that the solution-processed ZnO/AZO bilayer ETLs provide a promising new approach for the development of low-cost, high-performance, and stable planar perovskite solar cells.
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This study aims to improve the characteristics of AlGaInP-based micro light-emitting diodes (micro-LEDs) by utilizing three different passivation layers, including silicon dioxide (SiO2), distributed ...Bragg reflector (DBR), and aluminum oxide (Al2O3) grown by atomic layer deposition (ALD) in combination with DBR. In terms of transmittance and refractive indices, our proposed structure, constructed with ALD-grown Al2O3 and a nine-layered DBR, exhibits significant improvements in all aspects compared to the traditional structure with a 3000Å SiO2 passivation layer. Additionally, the structure demonstrates a 124.28% increase in external quantum efficiency (EQE) compared to the LED constructed with a nine-layered DBR. This result indicates that the ALD growth of Al2O3 effectively reduces sidewall losses, significantly impacting the improvement of micro-LEDs.
The efficiency of AlGaInP micro light-emitting diodes (micro-LEDs) was far weaker than that of GaN-based micro-LEDs in structure and performance. Consequently, there was an urgent demand to enhance ...their efficiency. In this study, a citric acid treatment strategy is proposed to improve the efficiency of red micro-LEDs, and the etching uniformity of different concentrations was first confirmed. We optimized the concentration of citric acid to 1:1 and modulated the wet etching time at 0, 30, 60, 90, and 120 s to treat the sidewalls of devices. Under an injection current density of 68 nA/cm 2 , the forward voltage (Vf) of micro-LEDs after soaking in citric acid ranged from 1.40 to 1.45 V. Compared with the sample operated at the forward voltage without citric acid sidewall treatment, AlGaInP micro-LEDs displayed significantly enhanced forward voltage. This indicates that citric acid effectively removed N-GaAs without damaging the electrical properties of the devices. Among all citric acid-treated micro-LEDs, the sample with a 60 s wet etching process showed the best improvement, with the light output power and external quantum efficiency (EQE) increased by 31.08% and 5.4%, respectively. Our proposed method to treat AlGaInP micro-LEDs presents promising opportunities for the future development of high-performance optoelectronics.
All-solution-processed reduced graphene oxide (rGO)-based flexible photodetectors (PDs) with asymmetric electrode structures of Ag nanowires (NWs) - Cu NWs are demonstrated for stable photodetection ...in weak-light environments. At first, we aimed to optimize the fabrication parameters of rGO layers for minimum roughness and high uniformity according to the field emission scanning electron microscope (FESEM) images; the average absorbance of optimal rGO layers is <inline-formula> <tex-math notation="LaTeX">\sim </tex-math></inline-formula>17.4% from 400 to 1600 nm. Additionally, compared to Ag NWs - Ag NWs and Cu NWs - Cu NWs electrodes, rGO PDs with Ag NWs-Cu NWs asymmetric electrodes showed a higher photocurrent-to-dark-current ratio (PDCR) (<inline-formula> <tex-math notation="LaTeX">\sim </tex-math></inline-formula>6), which was due to the improved carrier transport with using Ag and Cu as cathodes and anodes. Furthermore, the highest photoresponsivity (5.5 mA/W) and detectivity (<inline-formula> <tex-math notation="LaTeX">D^{\ast} </tex-math></inline-formula>) (<inline-formula> <tex-math notation="LaTeX">\sim {1}\times {10}^{{9}} </tex-math></inline-formula> cm Hz<inline-formula> <tex-math notation="LaTeX">^{{{1}/{2}}} </tex-math></inline-formula>/W) of rGO PDs with Ag NWs - Cu NWs electrodes have been measured and evaluated at 8 V bias. This work demonstrates the significant potential of all-solution processed rGO-based flexible PDs for high-performance and low-cost photosensing applications.
Bioenergy from photosynthetic living organisms is a potential solution for energy‐harvesting and bioelectricity‐generation issues. With the emerging interest in biophotovoltaics, extracting ...electricity from photosynthetic organisms remains challenging because of the low electron‐transition rate and photon collection efficiency due to membrane shielding. In this study, the concept of “photosynthetic resonator” to amplify biological nanoelectricity through the confinement of living microalgae (Chlorella sp.) in an optical micro/nanocavity is demonstrated. Strong energy coupling between the Fabry–Perot cavity mode and photosynthetic resonance offers the potential of exploiting optical resonators to amplify photocurrent generation as well as energy harvesting. Biomimetic models and living photosynthesis are explored in which the power is increased by almost 600% and 200%, respectively. Systematic studies of photosystem fluorescence and photocurrent are simultaneously carried out. Finally, an optofluidic‐based photosynthetic device is developed. It is envisaged that the key innovations proposed in this study can provide comprehensive insights in biological‐energy sciences, suggesting a new avenue to amplify electrochemical signals using an optical cavity. Promising applications include photocatalysis, photoelectrochemistry, biofuel devices, and sustainable optoelectronics.
A concept of a “living photosynthetic resonator” for amplifying bioelectricity through confinement of microalgae in an optical microcavity is demonstrated. The strong energy coupling between the cavity mode and photosynthetic resonance reveals the potential of exploiting optical resonators to amplify biological photocurrent generation and energy‐harvesting efficiency. Potential applications include photocatalysis, biophotovoltaics, and sustainable optoelectronics.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We demonstrated that hierarchical structures combining different scales (i.e., pyramids from 1.5 to 7.5 μm in width on grooves from 40 to 50 μm in diameter) exhibit excellent broadband and ...omnidirectional light-trapping characteristics. These microscaled hierarchical structures could not only improve light absorption but prevent poor electrical properties typically observed from nanostructures (e.g., ultra-high-density surface defects and nonconformal deposition of following layers, causing low open-circuit voltages and fill factors). The microscaled hierarchical Si heterojunction solar cells fabricated with hydrogenated amorphous Si layers on as-cut Czochralski n-type substrates show a high short-circuit current density of 36.4 mA/cm2, an open-circuit voltage of 607 mV, and a conversion efficiency of 15.2% due to excellent antireflection and light-scattering characteristics without sacrificing minority carrier lifetimes. Compared to cells with grooved structures, hierarchical heterojunction solar cells exhibit a daily power density enhancement (69%) much higher than the power density enhancement at normal angle of incidence (49%), demonstrating omnidirectional photovoltaic characteristics of hierarchical structures. Such a concept of hierarchical structures simultaneously improving light absorption and photocarrier collection efficiency opens avenues for developing large-area and cost-effective solar energy devices in the industry.
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