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Understanding the Performance of Organic Photovoltaics under Indoor and Outdoor Conditions: Effects of Chlorination of Donor Polymers
摘要： Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)] (PBDB-TS) and studied the effects of chlorine substitution of its thiophene-substituted benzodithiophene (BDT-Th) unit on its photovoltaic properties. The chlorination of the polymer resulted in a bulk heterojunction (BHJ) morphology optimized for efficient charge transport with suppressed leakage current and an increased open-circuit voltage of the OPV device; this optimization led to a remarkable enhancement of the OPV device’s power conversion efficiency (PCE) not only under the condition of 1 sun illumination but also under the condition of low light intensity mimicking indoor light; the PCE increased from 8.7% for PBDB-TS to ~13% for the chlorinated polymers, PBDT-TS-3Cl and PBDT-TS-4Cl, under the 1 sun illumination condition and from 5.3% for PBDB-TS to 21.7% for PBDB-TS-4Cl under 500 lx fluorescence illuminance. Interestingly, although the OPV PCEs under 1 sun illumination were independent of the position of chlorine substitution onto the polymer, the PBDB-TS-4Cl exhibited better performance under simulated indoor light than its derivative PBDB-TS-3Cl. Our results demonstrate that efficient light absorption and charge-carrier generation play key roles in achieving high OPV efficiency under low-light-intensity conditions.
关键词： bulk heterojunction,benzodithiophene,indoor light,chlorine substitution,organic photovoltaic
更新于2025-09-23 15:19:57
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Vacancies substitution induced interfacial dipole formation and defect passivation for highly stable perovskite solar cells
摘要： Although an efficient charge transport is essential to high-performance perovskite solar cells (PSCs), the serious charge trapping in perovskite films is still a barrier to improve the efficiency of PSCs. To overcome this issue, we efficiently suppress the charge trapping by using polar compound materials to reduce defects and improve the match of work functions in PSCs. 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) is used to form an interfacial dipole layer and triphenylphosphine oxide (TPPO) is employed to passivate defects. The interfacial dipole layer not only reduces the surface work function of electron transport layers (ETLs), but also substitutes organic/Cs cation vacancies. Oxygen atoms in TPPO molecules fill anion vacancies on perovskite crystal surfaces. As a result, the power conversion efficiency (PCE) of the champion PSCs has been improved to 21.1 % from 18.7 %. The target PSCs retained 98.3 % of its initial PCE after 214 days in dry air condition (relative humidity about 22 % at 25 ℃) due to the reduced defect density in perovskite.
关键词： vacancies substitution,Perovskite solar cells,triphenylphosphine oxide,[BMIM]BF4,charge transfer
更新于2025-09-23 15:19:57
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Highly Luminous Ba2SiO4a???′N2/3?′:Eu2+ Phosphor for NUV-LEDs: Origin of PL-Enhancement by N3a??-Substitution
摘要： Ba2SiO4?δN2/3δ:Eu2+ (BSON:Eu2+) materials with different N3? contents were successfully prepared and characterized. Rietveld refinements showed that N3? ions were partially substituted for the O2? ions in the SiO4-tetrahedra because the bond lengths of Si-(O,N) (average value = 1.689 ?) were slightly elongated compared with those of Si-O (average value = 1.659 ?), which resulted in the minute compression of the Ba(2)-O bond lengths from 2.832 to 2.810 ?. The average N3? contents of BSON:Eu2+ phosphors were determined from 100 nm to 2000 nm depth of grain using a secondary ion mass spectrometry (SIMS): 0.064 (synthesized using 100% α-Si3N4), 0.035 (using 50% α-Si3N4 and 50% SiO2), and 0.000 (using 100% SiO2). Infrared (IR) and X-ray photoelectron spectroscopy (XPS) measurements corroborated the Rietveld refinements: the new IR mode at 850 cm?1 (Si-N stretching vibration) and the binding energy at 98.6 eV (Si-2p) due to the N3- substitution. Furthermore, in UV-region, the absorbance of N3?-substituted BSON:Eu2+ (synthesized using 100% α-Si3N4) phosphor was about two times higher than that of BSO:Eu2+ (using 100% SiO2). Owing to the N3? substitution, surprisingly, the photoluminescence (PL) and LED-PL intensity of BSON:Eu2+ (synthesized using 100% α-Si3N4) was about 5.0 times as high as that of BSO:Eu2+ (using 100% SiO2). The compressive strain estimated by the Williamson?Hall (W?H) method, was slightly increased with the higher N3? content in the host-lattice of Ba2SiO4, which warranted that the N3- ion plays an important role in the highly enhanced PL intensity of BSON:Eu2+ phosphor. These phosphor materials could be a bridgehead for developing new phosphors and application in white NUV-LEDs field.
关键词： N3? substitution,Ba2SiO4:Eu2+,IR,PL,SIMS,XPS
更新于2025-09-23 15:19:57
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Theoretical investigation on the kinetics and mechanism of the synthesis of fluorescent 3,8-disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles
摘要： 3,8-Disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles show very interesting optical properties. In some cases, they have higher quantum yields compared to well-known fluorescent dyes such as fluorescein. Hitherto, no detailed theoretical study has been reported on the mechanism of the synthesis of the titled compounds, hence an accurate and detailed theoretical investigation on the synthesis of these dyes is desirable. In this paper, density functional theory (DFT) methods have been employed to investigate the most reasonable mechanism in formation of these fluorophores. All species and related transition states were optimised and the relative energies of all species and the activation energies for all proposed mechanisms were obtained. Comparing the Ea values of all pathways reveals that intramolecular electrophilic aromatic substitution is the most plausible mechanism for the cyclisation reaction in the preparation of these dyes. Also, the effects of substituents in positions 3 and 8 were investigated and the results show that electron-donor substituents can reduce the activation energy for formation of the σ complex in the electrophilic aromatic substitution.
关键词： kinetics,intramolecular electrophilic aromatic substitution,thermodynamics,5-a]acridine,DFT calculations,imidazo[4,substituent effects
更新于2025-09-19 17:15:36
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Effect of position and concentration of Li on ZnO physical properties : Density functional investigation
摘要： In this paper, we study the effect of Li position on the physical properties of Li doped ZnO with different concentrations (6.25%,12.5% and 18.75%), by using density functional theory and Boltzmann transport theory. In this work, two possible configurations of Li-doped ZnO are considered : substitution of Zn by Li atom (LiZn), and Li takes the interstitial position (Lii). It is found found that the position and the concentration of Li play an important role in determining the suitable applications for Li doped ZnO. It is also shown that the obtained results are in good agreement with experimental studies.
关键词： Li doped ZnO,Electronic Structure,First principles study,interstitial.,substitution
更新于2025-09-19 17:15:36
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Defect levels induced by double substitution of B and N in 4H-SiC
摘要： Studies of substitutional impurities in 4H-SiC play a major role in identifying the most enhanced defect levels induced. N and B substitution in 4H-SiC on separate studies reveal that the induced negative-U charge state ordering while the induced shallow acceptor level. In this report, in order to predict the most stable defect and its electrically active defect levels, the Heyd, Scuseria and Ernzerhof (HSE06) hybrid functional was used to model and predict the energetics and defect levels induced by double substitution of B and N pair (NBCC, NBSiC, NBCSi, NBSiSi) in a 4H-SiC. While both B and N substituted for C under equilibrium conditions is the most energetically favourable pair, the N and B both substituted for Si has a relatively high formation energy. The energies of the various configurations suggest that the substitution of B and N pair in 4H-SiC is always stable, and NBCC is the most energetically favourable defect. While all the defects studied induced acceptor levels, only the NBSiC and NBCSi induced shallow donor levels. The (0/?1) acceptor level induced by the defects is close to the conduction band minimum for the case of NBSiC and deep lying middle of the band gap of 4H-SiC for the NBCC and NBCSi.
关键词： Defect,Charge state,Formation energy,Substitution
更新于2025-09-19 17:15:36
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Sharpening the VNIR and SWIR Bands of Sentinel-2A Imagery through Modified Selected and Synthesized Band Schemes
摘要： In this work, the bands of a Sentinel-2A image with spatial resolutions of 20 m and 60 m are sharpened to a spatial resolution of 10 m to obtain visible and near-infrared (VNIR) and shortwave infrared (SWIR) spectral bands with a spatial resolution of 10 m. In particular, we propose a two-step sharpening algorithm for Sentinel-2A imagery based on modified, selected, and synthesized band schemes using layer-stacked bands to sharpen Sentinel-2A images. The modified selected and synthesized band schemes proposed in this study extend the existing band schemes for sharpening Sentinel-2A images with spatial resolutions of 20 m and 60 m to improve the pan-sharpening accuracy by changing the combinations of bands used for multiple linear regression analysis through band-layer stacking. The proposed algorithms are applied to the pan-sharpening algorithm based on component substitution (CS) and a multiresolution analysis (MRA), and our results are then compared to the sharpening results when using sharpening algorithms based on existing band schemes. The experimental results show that the sharpening results from the proposed algorithm are improved in terms of the spatial and spectral properties when compared to existing methods. However, the results of the sharpening algorithm when applied to our modified band schemes show differing tendencies. With the modified, selected band scheme, the sharpening result when applying the CS-based algorithm is higher than the result when applying the MRA-based algorithm. However, the quality of the sharpening results when using the MRA-based algorithm with the modified synthesized band scheme is higher than that when using the CS-based algorithm.
关键词： band selection and synthesis,Sentinel-2A sharpening,multiple linear regression,component substitution (CS),multiresolution analysis (MRA)
更新于2025-09-19 17:15:36
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Acetamidinium substituted methylammonium lead iodide perovskite solar cells with higher open-circuit voltage and improved intrinsic stability
摘要： We report Acetamidinium (AA) substituted methylammonium lead iodide perovskite solar cells. AA has a restricted C-N bond rotation, due to delocalized 3+ electron cloud over C-N bond and presence of an additional N-H bond (4H-bond in AA as compared to 3H-bond in MA). These bonding structures strengthen the electrostatic interaction and stabilizes the acetamidinium cation inside the perovskite matrix. AA, a larger cation, is substitutional only up to 10%. Devices made with 10% AA-substituted films show average Voc of 1.12 V, higher than the average Voc of 1.04 V in case of MAPbI3. This increase in Voc can be attributed to increase in carrier lifetime from 20 μs in case of MAPbI3 to 32 μs for 10% AA substituted films respectively. Devices with 18.29% champion and 16.3% average efficiency were fabricated for films with 10% AA. Degradation experiments confirm that the material stability also makes devices more stable; under ambient exposure (72–3% RH) devices with 10% AA retain 70% of their initial power conversion efficiencies (PCE) upto 480 h. Under same conditions, the PCE’s of reference MAPbI3 devices reduced to 43% of their initial value in 480h.
关键词： cation substitution,acetamidinium,solar cells,Halide perovskite,open circuit voltage,H-bonding,stability
更新于2025-09-19 17:13:59
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Boosting Photovoltaic Performance and Stability of Super-halogen Substituted Perovskites Solar Cells by Simultaneous Methylammonium Immobilization and Vacancy Compensation
摘要： Perovskite solar cells (PSCs) are susceptible to intrinsic structural instability associated with the presence of inorganic halide anions and organic cations vacancies, thus leading to the deterioration or even premature failure of devices. Herein, we develop an efficient strategy using super-halogen BH4- substitution to simultaneously immobilize methylammonium and substitute iodide vacancy for high performance PSCs based on the di-hydrogen bonding interactions. The introduced super-halogen BH4- groups not only significantly reduce the vacancies density but also effectively inhibit the decomposition of CH3NH3+ group by forming perovskite CH3NH3PbI3-x(BH4-)x. The power conversion efficiency (PCE) of the assembled mesoporous devices is remarkably promoted from 18.43% to 21.10%, accompanied by significant increase of both Jsc and Voc without obvious hysteresis. The superior PSCs can retain 90% and 80% of their initial PCE even after being stored for 1200 hours under environmental conditions (50 ± 10% RH) and 240 hours at 85 °C in dark, respectively. Moreover, it delivers excellent optical stability under ultraviolet illumination. This work provides an avenue to improve both the long-term stability and photovoltaic performance of PSCs.
关键词： stability,vacancy substitution,perovskite solar cells,super-halogen BH4-,methylammonium immobilization
更新于2025-09-19 17:13:59
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Efficient Nanorod Arrays Perovskite Solar Cells: A Suitable Structure for High Strontium-Substitution in a Nature Environment
摘要： Organic-inorganic hybrid perovskite solar cells (PSCs) have become a research hotspot because of their excellent power conversion efficiency (PCE), but the presence of toxic lead (Pb) in perovskite film has significantly limited their commercial application. In this study, using a TiO2 nanorod arrays (TNRAs) as the electron transport layer (ETL), strontium chloride (SrCl2) was chosen to fabricate lead-less PSCs in air environment (relative humidity, RH=50%) by a simple two-step spin-coating method. The influence of introduced strontium (Sr) on the perovskite films and cell properties was systematically investigated by various characterization methods. With increasing Sr substitution amount from 0 to 15 mol%, the formed perovskite films with a compact structure and a large crystalline size essentially remained invariable, while residual PbI2 was reduced, which is beneficial for the cell performance. The optimal PCE of 16.08% (average PCE = 15.37%) was obtained for the 5 mol% Sr-substituted PSCs because of the enhanced charge extraction from the perovskite film to the TNRAs and the suppressed charge recombination in the PSC. Both the humidity and thermal stability of the Sr-substituted PSCs were improved. More importantly, the 15 mol% Sr-substituted PSCs still exhibited a PCE of 15.09% in air (RH = 50%), maintaining 99% of the cell efficiency of the pristine (0 mol% Sr) PSC (15.27%), suggesting that the TNRAs structure is suitable for synthesis of high Sr-substituted lead-less PSCs.
关键词： Lead-less perovskite solar cells,TiO2 nanorod arrays,Defect density,Strontium substitution,Recombination
更新于2025-09-19 17:13:59