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Spin-dependent tunneling of light and heavy holes with electric and magnetic fields
摘要： The spin-dependent tunneling of light holes and heavy holes was analysed in a symmetrical heterostructure with externally applied electric and magnetic fields. The effects of the applied bias voltage, magnetic field and reverse bias were discussed for the polarization efficiency of light holes and heavy holes. The current density of spin-up and spin-down light holes increases as the bias voltage increases and reaches the saturation, whereas the current density of spin-up heavy holes is almost negligible. The applied bias voltage and the magnetic field highly influence the energy of resonance polarization, polarization efficiency, and the current density of heavy holes more than for the light holes.
关键词： heterostructure,reverse bias,current density
更新于2025-09-23 15:21:01
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Utility of copper oxide nanoparticles (CuO-NPs) as efficient electron donor material in bulk-heterojunction solar cells with enhanced power conversion efficiency
摘要： In the present work, we have endeavored the utilization of wet-chemically synthesized copper oxide nanoparticles (CuO-NPs) as the active layer in hybrid bulk heterojunction (BHJ) solar cells. The BHJs with CuO-NPs display significantly different physics from customary BHJs, and prove a noteworthy improvement in their performance. It is noted that with the addition of CuO-NPs, the morphology of the photoactive layer endures significant changes. Incorporating CuO-NPs is an additional paradigm for BHJs solar cells which enhances the photocurrent density from 9.43 mA/cm2 to 11.32 mA/cm2 and the external quantum efficiency as well. Also the power-conversion efficiency (PCE) improved from 2.85 % to 3.82 % without harming the open circuit voltage and the fill factor. The enhancement in PCE achieved here makes it worthy to design high-performance organic solar cells holding inorganic nanoparticles.
关键词： thin films,Bulk heterojunction,Solar cells,external quantum efficiency,Copper oxide nanoparticles,photo current density
更新于2025-09-23 15:19:57
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Suppressing Efficiency Roll-Off at High Current Densities for Ultra-Bright Green Perovskite Light-Emitting Diodes
摘要： Perovskite light-emitting diodes (PeLEDs) have undergone rapid development in the last several years with external quantum efficiencies (EQE) reaching over 21%. However, most PeLEDs still suffer from severe efficiency roll-off (droop) at high injection current densities, thus limiting their achievable brightness and presenting a challenge to their use in laser diode applications. In this work, we show that the roll-off characteristics of PeLEDs are affected by a combination of charge injection imbalance, nonradiative Auger recombination, and Joule heating. To realize ultrabright and efficient PeLEDs, several strategies have been applied. First, we designed an energy ladder to balance the electron and hole transport. Second, we optimized perovskite materials to possess reduced Auger recombination rates and improved carrier mobility. Third, we replaced glass substrates with sapphire substrates to better dissipate joule heat. Finally, by applying a current-focusing architecture, we achieved PeLEDs with a record luminance of 7.6 Mcd/m2. The devices can be operated at very high current densities (J) up to ~ 1 kA/cm2. Our work suggests a broad application prospect of perovskite materials for high-brightness LEDs and ultimately a potential for solution-processed electrically pumped laser diodes.
关键词： Joule heat,efficiency roll-off,Auger recombination,charge injection balance,high injection current density,ultrahigh brightness,perovskite light emitting diodes
更新于2025-09-23 15:19:57
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Photovoltaic cells with various azo dyes as components of the active layer
摘要： The photovoltaic response of six cells with an active layer of heterocyclic azo dyes is presented for the first time. The active azo layers differed in the type of substituent (i.e. electron-donating: CH3, OCH3 and electron withdrawing: Br). We showed that by changing the substituent in the heterocyclic azo dye we change the power efficiency of the device. It should be mentioned that all presented data showed high potential of heterocyclic azo dyes for effective photovoltaic output. The studied heterocyclic azo dyes have higher photovoltaic parameters than those obtained for photovoltaic cell with 4-Diethoxyphenylsilylazobenzene.
关键词： Theoretical DFT calculations,Photovoltaic cell,Thin films,Heterocyclic azo dyes,Current density-voltage characteristics
更新于2025-09-23 15:19:57
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An IC-level countermeasure against laser fault injection attack by information leakage sensing based on laser-induced opto-electric bulk current density
摘要： Laser fault injection (LFI) attack on cryptographic processor ICs is a critical threat to information systems. This paper proposes an IC-level integrated countermeasure by employing an information leakage sensor against this LFI attack. Distributed bulk current sensors monitor abnormal bulk current density caused by laser irradiation for LFI. A time-interleaved sensor operation and sensitivity tuning can obtain partial leakage bit information of secret key with small layout area penalty. Based on the leakage information, the secret key can be securely updated for realizing high-availability resilient systems. The test chip was designed and fabricated in 0.18μm standard CMOS, integrating a 128-bit Advanced Encryption Standard (AES) cryptographic processor with the proposed information leakage sensor.
关键词： information leakage sensor,cryptographic processor,Laser fault injection,AES,CMOS,bulk current density
更新于2025-09-23 15:19:57
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Tailoring optoelectronic properties of CH3NH3PbI3 perovskite photovoltaics using al nanoparticle modified PC61BM layer
摘要： In photovoltaics, light harvesting is one of the critical factors for the enhancement of power conversion efficiency (PCE). Photon harvesting can be carried out by various methods in perovskite photovoltaic. The improved light harvesting can also be achieved by trapping the light by incorporating metallic nanoparticles at the interface or in the perovskite active layer itself. Either light is absorbed or scattered by metallic nanoparticles depending on the particle size. When light is absorbed by the nanoparticles (size < 20 nm), it behaves like a sub-wavelength antenna due to localized surface plasmon resonance (LSPR) excitation and hence near field effect of plasmonic particle will be interacting to CH3NH3PbI3 active layer. Larger particles (> 20 nm) act as sub-wavelength scattering centers of light and help in trapping incident light. In order to make use of dual effect poly-dispersed spherical aluminium nanoparticles (AlNPs) (size – 20–70 nm) were incorporated in the CH3NH3PbI3 perovskite solar cell at the PC61BM/Al electrode interface. As a result, there is an increase in the optical absorption in the AlNPs embedded device. A detailed study of optical absorption, absorbed light emission characteristics charge trap density and carrier concentration studies, photovoltaic property measurements indicates, improvement in power conversion efficiency arise due to enhancement in JSC. Evaluated device properties indicate that enhancement in JSC arises due to improvement in the active layer photon absorption by both scattering and plasmonic effect in addition to reduced series resistance.
关键词： Trap states,Organic-inorganic halide perovskite solar cell,Ultraviolet plasmonic resonance,Plasmonic nanoparticle current density,Metal nanoparticles
更新于2025-09-23 15:19:57
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Role of electron leakage on efficiency droop in AlxGa(1a??x)N/GaN ultraviolet LEDs
摘要： Highly efficient AlxGa1?xN/GaN deep ultraviolet LEDs are widely used for water purification and medical diagnostics. However, these LEDs undergo efficiency reduction problem known as efficiency droop. Many causes of efficiency droop have been found; out of these one strong cause is electron leakage (EL). Electrons are leaked from the active region of the device before recombination. Electron leakage in AlxGa1?xN/GaN deep ultraviolet LEDs depends on temperature and carrier concentration. Here we investigate efficiency droop phenomenon of AlxGa1?xN/GaN deep ultraviolet LEDs under the effect of polarization charges on carrier concentrations. It is found that efficiency is decreased when polarization and applied current increases.
关键词： Electron leakage (EL),Efficiency droop,Current density,UV LED,IQE,AlGaN/GaN
更新于2025-09-23 15:19:57
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High Sensitivity Visible-Near Infrared Organic Photodetector Based on Non-fullerene Acceptor
摘要： Highly sensitive solution-processed organic photodetectors (OPDs) with a broadband response ranging from visible to near infrared (NIR) and excellent overall device performance are demonstrated. The OPDs were fabricated from a blend consisting of a wide bandgap polymer donor and a newly developed fused octacylic small-molecule electron acceptor with acceptor–donor–acceptor structure, which shows relatively high and balanced hole/electron mobility and allow for thicker photoactive layer (~300 nm). In conjunction with the use of an optimized inverted device structure, the dark current density of the OPDs was suppressed to an ultralow level of (8.3±5.5)×10-10A cm-2 at bias of –1 V and the capability to directly weak light intensity is down to 0.24 pW cm?2, both are among the lowest reported values for OPDs. Owing to the low shot noise enabled by the inverted structure and the low thermal noise due to the high shunt resistance of the device, the obtained OPDs shows spectrally flat photoresponse in the range of 350–950 nm (UV-Vis-NIR) and a maximal specific detectivity (D*) of (2.1±0.1)×1013 Jones at 800–900 nm, which is among the best results of NIR OPDs reported to date and represents a highly sensitive photodetector for weak optical signal detection. Besides, the OPDs shows a wide bandwidth of 30 kHz, fast temporal response time around 12 us ~14 us and a large linear dynamic range of 106 dB.
关键词： dark current density,specific detectivity,non-fullerene acceptors,weak optical signal detection,organic photodetectors
更新于2025-09-23 15:19:57
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Correlation between the open-circuit voltage and recombination loss at metal-silicon interfaces of crystalline silicon solar cells
摘要： For screen-printed silicon solar cells, optimization of the contact characteristics between the front metal electrode and silicon is very significant for realizing high efficiency. As technology advances, the solar cell efficiency has been steadily increased. Especially, as surface recombination becomes more important in high efficiency solar cells, understanding and controlling recombination in the metal contact area are necessary. Recombination at the metal-silicon interface is a major cause of the drop in the open-circuit voltage (Voc) of a solar cell. Thus far, the study of electrodes in silicon solar cells has been largely aimed at reducing the series resistance, and few studies on recombination due to electrodes have been performed. Quantitatively evaluating the recombination in electrodes to assess the effect on the efficiency is expected to become more important in the near future. In this paper, the contact characteristics of a screen-printed silver electrode and silicon interface were analyzed using saturation current density (Jo) measurements according to the surface doping concentration and firing temperature. The effects of the contact characteristics on Voc and recombination were also investigated. Experimental results showed that Jo.pass decreased with decreasing surface doping concentration and Jo.metal increased with increasing surface doping concentration and firing temperature. For quantitative analysis of Jo.metal, the size and distribution of Ag crystallites were observed using SEM and TEM, and the Ag concentration was analyzed by ICP-OES measurements. The larger Jo.metal was, the higher the Ag crystallite concentration, indicating that the Ag crystallites under the electrode increased Jo.metal. The effect of Jo.metal on the electrical characteristics of the solar cell was analyzed by calculating the change in the surface recombination velocity and the decreased width of Voc. Through this study, the recombination in the metallized area, which is expected to become increasingly important, and particularly the effects of the doping profile of the emitter region and silver crystallites on the surface recombination were quantitatively assessed. The amount of silver crystallites on the silicon wafer was quantitatively analyzed.
关键词： Screen-printed silicon solar cells,Saturation current density,Open-circuit voltage,Ag crystallites,Recombination loss,Metal-silicon interface
更新于2025-09-23 15:19:57
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Apparent delocalization of the current density in metallic wires observed with diamond nitrogen-vacancy magnetometry
摘要： We report on a quantitative analysis of the magnetic field generated by a continuous current running in metallic microwires fabricated on an electrically insulating diamond substrate. A layer of nitrogen-vacancy (NV) centers engineered near the diamond surface is employed to obtain spatial maps of the vector magnetic field, by measuring Zeeman shifts through optically detected magnetic resonance spectroscopy. The in-plane magnetic field (i.e., parallel to the diamond surface) is found to be significantly weaker than predicted, while the out-of-plane field also exhibits an unexpected modulation. We show that the measured magnetic field is incompatible with Ampère’s circuital law or Gauss’s law for magnetism when we assume that the current is confined to the metal, independent of the details of the current density. This result was reproduced in several diamond samples, with a measured deviation from Ampère’s law by as much as 94(6)% (i.e., a 15σ violation). To resolve this apparent magnetic anomaly, we introduce a generalized description whereby the current is allowed to flow both above the NV sensing layer (including in the metallic wire) and below the NV layer (i.e., in the diamond). Inversion of the Biot-Savart law within this two-channel description leads to a unique solution for the two current densities that completely explains the data, is consistent with the laws of classical electrodynamics, and indicates a total NV-measured current that closely matches the electrically measured current. However, this description also leads to the surprising conclusion that in certain circumstances the majority of the current appears to flow in the diamond substrate rather than in the metallic wire, and to spread laterally in the diamond by several micrometers away from the wire. No electrical conduction was observed between nearby test wires, ruling out a conventional conductivity effect. Moreover, the apparent delocalization of the current into the diamond persists when an insulating layer is inserted between the metallic wire and the diamond or when the metallic wire is replaced by a graphene ribbon. The possibilities of a measurement error, a problem in the data analysis, or a current-induced magnetization effect are discussed, but do not seem to offer a more plausible explanation for the effect. Understanding and mitigating this apparent anomaly will be crucial for future applications of NV magnetometry to charge transport studies.
关键词： diamond magnetometry,nitrogen-vacancy centers,Biot-Savart law,Ampère's law,magnetic field imaging,current density
更新于2025-09-19 17:15:36