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Generation-recombination voltage noise spectrum in uniformly doped majority-carrier semiconductor samples
摘要： The formula for the voltage noise spectrum due to generation-recombination (G-R) rate fluctuations is derived for uniformly doped majority-carrier n-type semiconductor samples. In the derivation of the formula, the ohmic boundary condition is used to obtain physically sound results, correcting and extending the previously published formulas. It is shown that the G-R voltage noise spectrum becomes saturated in the high electric field region, which is the signature feature of the G-R noise. Furthermore, the electron density fluctuation is developed and calculated due to the delta-function population source. It is shown that as the electric field increases, the profile of the electron density fluctuation becomes quite asymmetric due to the strong drift velocity, and the peak value of the electron density fluctuation at the delta-function source location decreases, resulting in the saturation of the G-R noise voltage spectrum at high electric fields.
关键词： generation-recombination noise,voltage noise spectrum,semiconductor,electron density fluctuation,electric field
更新于2025-09-23 15:21:01
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Alternative buffer layers in Sb2Se3 thina??film solar cells to reduce opena??circuit voltage offset
摘要： Antimony Selenide (Sb2Se3) thin-film solar cell configurations with alternative buffer layers are proposed to improve the efficiency by minimizing open‐circuit voltage offset (Voc,offset). The conduction band offsets have been optimized not only at absorber/buffer (ΔEC‐BA) but also at buffer/transparent conductive oxide (ΔEC-TB). Voltage‐independent recombination rates in the quasi‐neutral region (Rb0), and at the absorber/buffer interface (Ri0) of the Sb2Se3 solar cells with various configurations are individually modelled. The development of cell configurations causes to decrease the Ri0, and Rb0, consequently reducing the Voc,offset. It is found that the solar cell configuration of Mo/MoSe2/Sb2Se3/TiO2/ZnO0.4S0.6/Zn0.93Mg0.07O/ZnO:Al is suitable with the ΔEC‐BA of 0.29 eV and ΔEC‐TB of ?0.2 eV, therefore considerably reducing Voc,offset to approximately 0.52 V, and improving the efficiency to 15.46%.
关键词： Recombination rate,Sb2Se3,Open‐circuit voltage offset,Device configuration,Alternative buffer layers
更新于2025-09-23 15:21:01
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One Dimensional CdS Nanotube vs CdS Bulk Structure for Photocatalytic Water Splitting: Role of Dimensionality
摘要： Using the state-of-the-art density functional theoretical calculations, we have modelled a facetted CdS nanotube (NT) catalyst for photocatalytic water splitting. The overall photocatalytic activity of the CdS photocatalyst has been predicted based on the electronic structures, band edge alignment, and overpotential study. For comparisons, we have also investigated the water spilitting process over the CdS bulk structure. The band edge alignment along with oxygen evolution reaction/hydrogen evolution reaction (OER/HER) mechanism studies help us to find out the effective overpotential for the overall water splitting on these surfaces. Our study shows that CdS NT has highly stabilized valence band edge compared to that in the CdS bulk due to strong p-d mixing. Such highly stabilized valence band edge is important for the hole-transfer process and reduces the risk of electron-hole recombination. Such nanotube requires less overpotential for water oxidation reaction than the periodic CdS. All these suggest that the efficiency of water oxidation/reduction process further improves in CdS as we reduce its dimensionality. More importantly, we report here that there are two factors, which makes CdS nanotube as a better photocatalyst material compared to its bulk counterpart. Furthermore, the stabilized valence band edge is good for their photostability too as bulk CdS suffers from photostability.
关键词： photocatalysis,HER,CdS nanotube,OER,electron-hole recombination
更新于2025-09-23 15:21:01
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Temperature dependence of nonradiative recombination processes in UV-B AlGaN quantum well revealed by below-gap excitation light
摘要： Nonradiative recombination (NRR) processes through defect states and their temperature dependence in UV-B AlGaN MQW sample on sapphire substrate grown by MOCVD technique have been studied by photoluminescence (PL) spectroscopy. We detected NRR centers by adding a below-gap excitation light with photon energies from 0.93 eV to 1.46 eV on an above-gap excitation light of 4.66 eV. All the BGE energies decreased PL intensity at 25 K, and the most-distinct quenching is observed by 1.27 eV BGE at the same BGE photon number density. The temperature-dependent PL intensity for the BGE energy of 1.27 eV is interpreted by three NRR centers. The one-level model dominates over that of two-level model in the temperature range 58 K < T < 88 K. The two-level model prevails in other region of temperature. The combination of one-level and two-level models is consistent with the spectral peak-energy shift as a function of temperature.
关键词： AlGaN,Quantum well,Two-wavelength excited photoluminescence,Recombination model,Nonradiative recombination center
更新于2025-09-23 15:19:57
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Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells
摘要： Interface engineering is an effective means to enhance the performance of thin film devices, such as perovskite solar cells (PSCs). Here, a conjugated polyelectrolyte, poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethyl-ammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]di-iodide (PFN-I), is employed at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer (ETL) simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF), resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 hours of exposure to a relative humidity 35-55 % at room temperature. All of these improvements are attributed to the functional PFN-I layers as they provide favorable interface contact and defect reduction.
关键词： perovskite solar cells,non-radiative recombination,conjugated polyelectrolytes,interface engineering
更新于2025-09-23 15:19:57
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Efficient phenothiazine-ruthenium sensitizers with high open-circuit voltage (Voc) for high performance dye-sensitized solar cells
摘要： Herein, we designed and synthesized two highly effective phenothiazine-ruthenium sensitizers JR1 and JR2 to use in dye-sensitized solar cells. The structure of N719 was further optimized, 1,10-phenanthroline modified by phenothiazine was used instead of 2,2'-bipyridine-4,4'-dicarboxylic acid to as the electron donor. Compared with N719, these two ruthenium dyes show better optical properties, both the spectral response range and the molar absorption coefficient of dye molecules have been significantly improved. The IPCE response of JR1 is obviously improved, the response range of photocurrent is widened to 800 nm, the overall response value is also higher. JR2 shows the widest and highest IPCE response curve, in the region of 410-600 nm, the IPCE value of JR2 is more than 70%, and at 530 nm, the IPCE value has reached 79%, so JR2 shows the highest Jsc of 17.18 mA cm-2. Further optimization of molecular structure not only improves the light-harvesting performance of the device, but also reduces the charge recombination behaviour and improves the the electron lifetime, so the Voc is greatly increased. Especially for JR2, the introduction of the second long carbon chain not only increases the solubility of the dye, but also further suppresses the dye aggregation and reduces the charge recombination. The phenothiazine-ruthenium dye JR2 shows a high Voc of 841 mV, while the theoretical Voc of DSSCs based on I-/I3 - electrolyte is about 900 mV. JR2 exhibits a superior PCE of 9.12%, which exceeds N719 (8.03%) about 14%.
关键词： Phenothiazine,Ruthenium sensitizers,Dye-sensitized solar cells,Charge recombination
更新于2025-09-23 15:19:57
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Nitrogen doping of TiO2 and annealing treatment of photoanode for enhanced solar cell performance
摘要： Mild doping of nitrogen (N) in TiO2 followed by an optimized aerial annealing treatment of CdS quantum dot (QD) sensitized photoanode resulted in ef?cient electron transfer and low recombination rates for the corresponding quantum dot solar cell (QDSC). Nitrogen doping passivates the surface defects in TiO2, reduces the density of recombination centers, and promotes electron injection into the current collector. N-doping also modi?es the electronic band structure of TiO2 and reduces the band gap from 3.17 to 2.91 eV. Therefore in the QDSC with the N-TiO2/CdS photoanode, both N-TiO2 and CdS, undergo charge separation upon illumination thereby producing a higher photocurrent compared to the undoped-TiO2/CdS based QDSC. N-doping also increased the redox activity of TiO2, allowing facile ion and electron transport across its cross-section which is advantageous for solar cell performance. Optimal annealing temperature of 150 (cid:1)C for the N-TiO2/CdS or TiO2/CdS photoanode restricted the back electron movement effectively, and imparted a signi?cantly enhanced power conversion ef?ciency (PCE) to the N-TiO2/CdS@150 (cid:1)C/polysul?de gel/C-fabric- solar cell, greater by 55% compared to its unannealed counterpart. Lowered average excited electron lifetime, increased-incident photon-to-current conversion ef?ciency, recombination resistance and photovoltage decay response time, con?rm the ability of the annealed photoanodes to undergo enhanced charge separation contrasting with the unannealed photoanode. This ?rst time study relies on two simple approaches of nitrogen doping and annealing treatment to achieve considerably improved photovoltaic parameters, and opens up realistic possibilities for commercialization of QDSCs.
关键词： Annealing treatment,Recombination,Charge transfer,N-doping,Solar cell
更新于2025-09-23 15:19:57
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Highly luminescent and stable CH3NH3PbBr3 quantum dots with 91.7% photoluminescence quantum yield: Role of guanidinium bromide dopants
摘要： Although perovskite quantum dots (PQDs) have received considerable attention, defects in PQDs can significantly degrade the properties and device performance. In this study, we report on an effective strategy for synthesizing highly luminescent CH3NH3PbBr3 quantum dots (QDs) by a simple doping. To remove such defects, guanidinium bromide (GuBr) was doped into the CH3NH3PbBr3 QDs synthesized by the ligand-assisted reprecipitation technique. From XRD and TEM studies, the doping of GuBr into the QD lattices was verified. In addition, the surfaces of PQDs with and without GuBr dopants were analyzed by XPS to trace the metallic Pb acting as a major recombination center. The GuBr doping resulted in the size uniformity of QDs and effectively eliminated defects and metallic Pb, which enhanced the photoluminescence quantum yield (PLQY) through the inhibition of the non-radiative recombination pathway. Furthermore, the recombination dynamics in the QDs were examined by using time-resolved photoluminescence and fluorescence lifetime imaging to verify the role of GuBr dopants. By optimizing the amount of GuBr doping, the CH3NH3PbBr3 QDs with strong green emission achieved a maximum PLQY of 91.7%.
关键词： Photoluminescence quantum yield,Fluorescence lifetime imaging,CH3NH3PbBr3 quantum dots,Guanidinium bromide,Recombination centers
更新于2025-09-23 15:19:57
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Carrier transport and recombination dynamics of InAs/GaAs sub-monolayer quantum dot near infrared photodetector
摘要： Here, we present a relative study of tunnel-induced photocarrier escape processes in a laterally coupled InAs sub-monolayer quantum dot-based photodetector (SML QD-PD) as a function of fractional coverage from 0.4 ML to 0.8 ML. Both by simulation and experiment, we have quantitatively described the temperature dependent interband photoresponse spectrally tuned in the near infrared region (835 nm–890 nm) on the basis of mutual competition between the interband carrier recombination and interdot tunneling lifetime with varying SML coverage. The progressively increasing recombination lifetime and decreasing interdot tunneling lifetime with increasing SML coverage has attributed to a faster photoresponse and greater responsivity. At higher coverage fraction, tunnel induced fast speed photocarrier transit through lateral array of SML QDs has been found to be capable of offering a faster temporal response (100 μs) with faithful reproducibility up to higher frequencies (1.3 KHz). Here, we report a powerful strategy to simultaneously tune responsivity, speed of time response and detectivity by externally controlling the SML coverage. This time response is measured to be nine times faster than a conventional SK QD photodetector. With increased coverage, inhibition of dark current due to trapping of injected charge carriers up to higher temperatures have resulted in high sustainable photodetectivity of 8 × 1011 cm Hz1/2 w?1 at ~250 K that offers near room temperature photodetection.
关键词： photoconductive gain,quantum dot photodetector,inter-dot tunneling,submonolayer coverage,near-infrared photoresponse,recombination dynamics,temporal photoresponse
更新于2025-09-23 15:19:57
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High performances red phosphorescent organic light-emitting diodes with low operation voltage
摘要： In this work, we demonstrated an efficient device design strategy in improving the electroluminescent performances of red phosphorescent emitter iridium(III) bis(2-phenylquinoly-N,C2’)dipivaloylmethane (PQ2Ir(dpm)) by constructing predominant and supplementary light-emitting layers (EMLs). 4,4’,4’’-tris(carbazole-9-yl) triphenylamine (TcTa) and 4,7-dicarbazol-9-yl-[1,10]-phenanthroline (BUPH1) were selected as host materials of EMLs. Due to the well-designed double-EMLs device structure and the well-matched energy levels of selected materials, improved carriers’ balance and broadening recombination zone caused the low operation voltage and high device performances. Finally, the 4 wt% double-EMLs device obtained the highest brightness, external quantum efficiency, current efficiency, and power efficiency up to 29870 cd m-2, 12.18%, 19.74 cd A-1, and 25.84 lm W-1, respectively. At very low operation voltage of 3.4 V, this device realized the certain brightness of 1000 cd m-2 with power efficiency of 14.68 lm W-1.
关键词： recombination zone,carriers’ balance,electroluminescence,operation voltage
更新于2025-09-23 15:19:57