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: Why Sn substitution should be preferred to Pb vacancy for optimum solar cell efficiency
摘要： Methylammonium lead halide (MAPbI3) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-(cid:2)) are addressed in regulating stability and solar cell ef?ciency of MAPb1?X ?Y SnX (cid:2)Y I3 perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron’s self-interaction error are examined carefully. We ?nd to reduce the Pb content from pristine MAPbI3, Sn substitution has a more favorable thermodynamic stability than creating Pb-(cid:2). Moreover, on substituting Sn, due to strong s-p and p-p couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coef?cient (redshifted) and maximum solar cell ef?ciency in MAPb1?X SnX I3 for 0 < X (cid:2) 0.5.
关键词： spin-orbit coupling,MAPbI3,solar cell efficiency,Pb vacancy,thermodynamic stability,Sn substitution,Methylammonium lead halide,hybrid density functional theory,optical absorption coefficient
更新于2025-09-19 17:13:59
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Fluoro-substitution in hydrogen bonding liquid crystal benzoic acid: dielectric, electro-optic and optical proprieties and inducing polar nematic phase
摘要： Dielectric and electro-optic properties have been studied in order to understand the effect of the fluoro-substitution on hydrogen bonded liquid crystal proprieties. The fluoro-substitution alters the characteristics of pure LC structure and changes its physical parameters. In the present paper, variation in physical parameters like dielectric permittivity, response time, elastic constant, rotational viscosity etc. has been explained based on many factors. In addition, the fluorine substitution has lead to the appearance of the polar nematic phase.
关键词： dielectric anisotropy,polar nematic,Hydrogen bonded liquid crystal,electro-optical properties,fluoro-substitution
更新于2025-09-19 17:13:59
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Uncovering details behind the formation mechanisms of Cu <sub/>2</sub> ZnGeSe <sub/>4</sub> photovoltaic absorbers
摘要： Among the thin film chalcogenide photovoltaic community there is an increasing interest in the study of cationic and anionic substitution in the di?erent absorber materials, including CdTe, chalcopyrites – Cu(In,Ga)(S,Se)2 and kesterites – Cu2ZnSn(S,Se)4. In the last case, cationic substitution has been revealed as a key factor to solve or palliate to some extent part of the fundamental problems of the kesterite technology. Among the different possibilities, the partial or total substitution of Sn by Ge is one of the most promising options, with proved excellent results from very small up to almost complete replacement. In view of the relevance of Ge in kesterite, this work presents the complete analysis of the reaction formation of the Cu2ZnGeSe4 (CZGeSe) compound using a sequential process based on the sputtering of elemental stacked layers followed by reactive annealing under Se atmosphere, by implementing a break-off experiment. An unusual solid–liquid–vapor extended growth mechanism is observed, thanks to the previous formation of a eutectic GeSe9 liquid phase that melts at temperatures above 212 1C. Driven by this liquid phase, it is demonstrated that CZGeSe formation mechanisms follow a strict sequence, starting from more simple molecules (binary compounds), then evolving to the ternary one, and finally to the quaternary alloy which is formed through the reaction of Cu2GeSe3 and ZnSe solid phases. The relevance of the study is supported by the solar cells prepared with these absorbers, demonstrating conversion efficiency at the level of the best reports in the literature. Finally, possible strategies to manage this singular formation pathway are discussed.
关键词： Ge substitution,photovoltaic,Cu2ZnGeSe4,formation mechanisms,thin film,kesterite
更新于2025-09-19 17:13:59
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Lithium-assisted synergistic engineering of charge transport both in GBs and GI for Ag-substituted Cu2ZnSn(S,Se)4 solar cells
摘要： Although silver (Ag) substitution offers several benefits in eliminating bulk defects and facilitating interface type inversion for Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic (PV) technology, its further development is still hindered by the fairly low electrical conductivity due to the significant decrease of acceptors amount. In this work, a versatile Li-Ag co-doping strategy is demonstrated to mitigate the poor electrical conductivity arising from Ag through direct incorporating Li via postdeposition treatment (PDT) on top of the Ag-substituted CZTSSe absorber. Depth characterizations demonstrate that Li incorporation increases p-type carrier concentration, improves the carrier collection within the bulk, reduces the defects energy level as well as inverts the electric field polarity at grain boundaries (GBs) for Ag-substituted CZTSSe system. Benefiting from this lithium-assisted complex engineering of electrical performance both in grain interior (GI) and GBs, the power conversion efficiency (PCE) is finally increased from 9.21% to 10.29%. This systematic study represents an effective way to overcome the challenges encountered in Ag substitution, and these findings support a new aspect that the synergistic effects of double cation dopant will further pave the way for the development of high efficiency kesterite PV technology.
关键词： Ag substitution,Alkali doping,Cu2ZnSn(S,Se)4,Thin film solar cell,Post-treatment
更新于2025-09-19 17:13:59
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High-yielding Pd <sub/>2</sub> (dba) <sub/>3</sub> ·C <sub/>6</sub> H <sub/>6</sub> -based four-fold Sonogashira coupling with selenophene-conjugated magnesium tetraethynylporphyrin for organic solar cells
摘要： A catalytic system using Pd2(dba)3$(C6H6)/PPh3/CuI for Sonogashira coupling was demonstrated to synthesize a selenophene-conjugated magnesium tetraethynylporphyrin Mg-TEP-(Se-DPP)4 (2a). The terminal alkynes of magnesium tetraethynylporphyrin with bromoselenophene-tethered diketopyrrolopyrroles (DPPs) to produce the desired star-shaped 2a in 80% yield. This molecule shows higher solubility in organic solvents, more efficient visible and near-infrared region absorption, and a narrower band gap compared with reference thiophene-conjugated congeners. Two strategies, namely, selenium substitution and end-capping, were investigated to optimize bulk heterojunction structures in the active layers of organic solar cells. The optimized device based on 2a:PC61BM exhibited the highest PCE of 6.09% among the tested devices after solvent vapor annealing, owing to efficient exciton dissociation, balanced carrier mobility, and suppressed carrier recombination in the film's ordered morphology.
关键词： end-capping,selenium substitution,Sonogashira coupling,selenophene-conjugated magnesium tetraethynylporphyrin,organic solar cells
更新于2025-09-16 10:30:52
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Efficient Two-Dimensional Tin Halide Perovskite Light-Emitting Diodes via a Spacer Cation Substitution Strategy
摘要： Lead halide perovskites have attracted tremendous attention due to their impressive optoelectronic properties. However, the toxicity of lead remains to be a bottleneck for further commercial development. Two-dimensional Ruddlesden-Popper tin-based perovskites are lead-free and more stable compared to their 3D counterparts, which have great potential in the optoelectronic device field. Herein, we demonstrated high-quality 2D phenylethyl ammonium tin-iodide perovskite (PEA2SnI4) thin films by dropping toluene as anti-solvent. Furthermore, the PeLED performance is greatly improved by replacing PEAI spacer cation with 2-thiopheneethyllamine iodide (TEAI). As a result, the TEA-based PeLED device is achieved with a low turn-on voltage of 2.3V, a maximum luminance of 322 cd m-2 and maximum external quantum efficiency of 0.62%, which is the highest efficiency and brightness for pure red (emission peak=638 nm) tin-based PeLEDs so far.
关键词： pure red light-emitting diodes,two-dimensional tin-based perovskite,spacer cation substitution
更新于2025-09-16 10:30:52
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Fluorescent 2-(pyridin-2-yl)vinyl pyridine dyes and their thermo-controlled release
摘要： The generation of unique thermosensitive fluorescent dyes via heteroaromatic Heck cross-coupling and N-pyridin-2-yl nucleophilic substitution was described. To demonstrate thermosensitive properties, the precursor was converted into carbonate or phosphate and heating at various temperatures and times of heating. Significant changes in fluorescence intensity and emission wavelengths, between carbonates and the cyclic product, were observed and proved that dyes may serve as removable fluorescent labels with large Stokes shifts (>80 nm). Application of thermosensitive fluorescent dyes in oligonucleotide labelling has been demonstrated.
关键词： Heck cross-coupling,large Stokes shifts,N-pyridin-2-yl nucleophilic substitution,thermosensitive fluorescent dyes,oligonucleotide labelling
更新于2025-09-16 10:30:52
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A New Co-Substitution Strategy as a Model to Study a Rare-Earth-Free Spinel-Type Phosphor with Red Emissions and Its Application in Light-Emitting Diodes
摘要： The substitution of metal sites in Mg2TiO4 substrate leads to charge imbalance that will be closely related to a variety of changes including lattice structure, cell distortion, and photophysical properties. Herein, the co-substitution strategy of [Ga3+?Ga3+] for [Mg2+?Ti4+] and Sn4+ for Ti4+ achieves for the first time the novel Mg3Ga2SnO8 (MGS):xMn4+ (x = 0?3%) phosphors with efficient red emissions. In terms of X-ray powder diffraction (XRD) and Rietveld refinement analysis, MGS:Mn4+ possesses a structure isotypic of Mg2TiO4 in the cubic space group Fd3?m (227). There are two types of octahedra for Mn4+ ions in this structure, where Ga3+ ions completely occupy a group of octahedral sites and Mg2+/Sn4+ has been randomly distributed over another group of octahedral sites. A strong excitation band in the broad spectral range (220?550 nm) has been identified, thus facilitating the commercial uses for blue LED chips excitation. An intense red emission band at 680 nm has been observed due to the characteristic 2Eg?4A2g transition of Mn4+ ions. A concentration quenching effect occurs when the Mn4+ content exceeds 1.5%, and the quenching mechanism is demonstrated to be dipole?quadrupole interactions. Temperature-dependent luminescence measurements support its good thermal stability, and the corresponding activation energy Ea is determined to be 0.2552 eV. The possible luminous mechanism of the Mn4+ ion is explained by the Tanabe?Sugano energy level diagram. The crystal field strength and the Racah parameters together with the nephelauxetic ratio are also determined for Mn4+ in the MGS lattice. High color rendition warm white-light-emitting diodes (WLEDs) based on the optimal phosphor MGS:1.5%Mn4+,1.5%Li+ possess a color rendering index and color temperature of 85.6 and 3658 K, respectively. Its feasibility for application in solid-state white lighting has been verified.
关键词： Co-substitution strategy,Light-emitting diodes,Red emissions,Spinel-type phosphor,Rare-earth-free
更新于2025-09-12 10:27:22
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Understanding of Imine Substitution in Wide Bandgap Polymer Donor–Induced Efficiency Enhancement in All-Polymer Solar Cells
摘要： All-polymer solar cells (all-PSCs) are proven to possess outstanding thermal and mechanical stabilities. However, concurrently achieving appropriate phase-separated pattern, efficient charge transportation, and adequate charge transfer between donor and acceptor components is still a challenge, and thus, only a few polymer-polymer BHJ blends have yielded BHJ device PCEs >8%. Generally, polymer backbone substitutions may have a direct influence on the device performance. Thus, this report examines a set of wide bandgap polymer donor analogues composed of thienothiophene (TT) or thiazolothiazole (TTz) motif, and their all-PSC device performance with N2200. Results show that all-PSCs based on the imine-substituted derivative PBDT-TTz exhibit power conversion efficiencies (PCE) as high as 8.4%, which largely outperform the analogue PBDT-TT-based ones with PCEs of only 0.7%. This work reveals that the imine substitution in polymer backbones of PBDT-TTz not only increases the ionization potential (IP) and electron affinity (EA), narrows the optical gap (Eopt), but also has significantly impacts on the BHJ film morphologies. PBDT-TTz:N2200 BHJ blends present better miscibility, suppressed phase separation, much stronger crystallinity, and face-on ordering, which are contributed to efficient exciton dissociation, charge transportation, and therefore, high-efficiency in all-PSCs. This study demonstrates that the imine-substituted polymers composed of TTz motif, which can be easily synthesized through a facile two-step procedure, are a promising class of wide bandgap polymer donors for efficient all-PSCs.
关键词： Imine substitution,All-polymer solar cells,Thiazolothiazole,Wide bandgap polymer donors,BHJ film morphologies
更新于2025-09-12 10:27:22
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Understanding the Impact of Side-chain on Photovoltaic Performance in Efficient All-polymer Solar Cells
摘要： In order to understand the impact of side-chain on photovoltaic performance and explore efficient All-polymer solar cells, chemical modifications on donor-acceptor based polymers containing benzo[1,2-b:4,5-b’]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) backbones were performed. Via side-chain fluorination, the molecular design resulted in lower highest occupied molecular orbital (HOMO) energy levels and enhanced backbone planarity. The intermolecular packing and solid-state ordering were found to significantly improve. These factors are considered as key influences for carrier transport. In contrast, introducing a bulky alkylthio substituent group was found to slightly distort the polymer backbone. As a result of the lower HOMO level, PTF8 exhibits an improved open circuit voltage (Voc) compared to the template polymer PT8. However, due to the increased crystallinity and aggregation, PTF8 and PTS8 experience an unfavorable phase separation in polymer-polymer bulk heterojunction blends, hindering the PCE to about 4%. Through introducing alkylthio side-chains and fluorination, the polymer PTFS8 exhibits an extremely low HOMO level (-5.73 eV). These reduced HOMO level limits charge separation between the donor and acceptor polymers. Without any fluorination and alkylthio side-chains, the wide bandgap polymer PT8 exhibits desired HOMO energy levels and crystallinity, delivering a best PCE of 8% together with a high Voc of 1.05 V, displaying its great potential for applications in efficient all-polymer optoelectronic devices.
关键词： BDT-TPD backbone,side-chain,fluorination,All-polymer solar cells,alkylthio substitution,photovoltaic performance
更新于2025-09-12 10:27:22