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Efficient charge generation at low energy losses in organic solar cells: a key issue review
摘要： Light absorption generates strongly bound excitons in organic solar cells (OSCs). To obtain efficient charge generation, a large driving force is required, which causes a large energy loss (Eloss) and severely hinders the improvement in the power conversion efficiencies (PCEs) of OSCs. Recently, the development of non-fullerene OSCs has seen great success, and the resulting OSCs can yield highly efficient charge generation with a negligible driving force, which raises a fundamental question about how the excitons split into free charges. From a chemical structure perspective, the molecular electrostatic potential differences between donors and acceptors may play a critical role in facilitating charge separation. Although the Eloss caused by charge generation has been suppressed, charge recombination, particularly via non-radiative pathways, severely limits further improvements in the PCEs. In OSCs with negligible driving forces, the lowest excited state, a hybrid local exciton-charge transfer state, is believed to have a strong association with the non-radiative Eloss. This review discusses the efficient charge generation at low Eloss values in highly efficient OSCs and highlights the issues that should be tackled to further improve the PCEs to new levels (~ 20%).
关键词： energy loss,organic solar cells,non-fullerene acceptors,electrostatic potential,charge generation
更新于2025-09-23 15:21:01
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Energetics and Energy Loss in 2D Ruddlesdena??Popper Perovskite Solar Cells
摘要： 2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA)2(MA)n?1PbnI3n+1/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces (n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios (n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open-circuit voltage (Voc) in the perovskite solar cells (PSCs) based on the 2D RPP (n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the Voc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such Voc improvement is attributed to the enhanced potential at the interface.
关键词： energy loss,2D Ruddlesden–Popper perovskites,open-circuit voltage,perovskite solar cells,energetics
更新于2025-09-23 15:21:01
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Synthesis of yttrium iron garnet/bismuth quantum dot heterostructures with localized plasmon enhanced magneto-optical performance
摘要： Interactions between light and magnetic matter attracted great attention lately due to their potential applications in nanophotonics, spintronics, and high-accuracy sensing. Here, we grew bismuth quantum dots (Bi–QDs) with strong spin–orbit coupling on a magnetic insulator yttrium iron garnet (YIG) via molecular beam epitaxy. The YIG/Bi–QDs material shows an enhanced magneto-optical Kerr rotation up to 130 % compared with that of a bare YIG film. The Bi–QDs were also introduced onto a lutetium–bismuth co-doped YIG film to form a hybrid system with remarkably enhanced Kerr rotation (from 1626 to 2341 mdeg). Ferromagnetic resonance measurements showed an increased effective magnetization as well as interfacial spin–orbit field in the YIG/Bi–QD heterostructures. Localized plasmons were mapped using electron energy loss spectroscopy with high spatial resolution, revealing enhanced plasmon intensity at both the Bi–QD surface and YIG/Bi–QD interface. Introducing Bi-QDs onto the YIG film enhanced Kerr rotation owing to the attenuated optical reflection and increased effective magnetization. The Bi–QD-enhanced magneto-optical effect enables development of efficient nanoscale light switching, spintronics, and even plasmonic nano-antennas.
关键词： Electron energy loss spectroscopy,Surface plasmon resonance,Bismuth quantum dot,Ferromagnetic resonance,Magneto-optical materials
更新于2025-09-23 15:21:01
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European Microscopy Congress 2016: Proceedings || Characterizing Localized Surface Plasmons using Electron Energy-Loss Spectroscopy
摘要： Localized surface plasmon resonances (LSPRs) are the coherent and collective oscillations of conduction band electrons at the surface of metallic nanoparticles. LSPRs are known to localize far-field light to a sub-diffraction-limited length scale, yielding an intense electric field at the particle surface. This effect has been harnessed to dramatically enhance light-matter interactions, leading to a variety of applications such as surface-enhanced Raman spectroscopy (SERS), photothermal cancer therapy and solar energy harvesting. Though a variety of near- and far-field optical methods are used to probe LSPRs, the spatial resolution of these methods is on the order of tens of nanometers, limiting their effectiveness. In contrast, electron energy loss spectroscopy (EELS) performed in a scanning transmission electron microscope (STEM) combines sub-nanometer resolving power with the capability to excite both optical-accessible and –inaccessible plasmon modes and therefore has emerged as one of the leading techniques (Figure 1). In this presentation, I will briefly introduce the STEM/EELS technique and demonstrate the power of STEM/EELS in the characterization of LSPRs. In addition to the traditional use of STEM/EELS for LSPR imaging, we have recently demonstrated that STEM/EELS can also be used to spatially map LSP-semiconductor energy transfer at the nanoscale. The future of STEM/EELS as a window into the nanoscopic world is especially promising, and we expect continued advances in the molecular, optical, materials, information, and energy sciences as a result.
关键词： Localized Surface Plasmon,Hot Electrons,Scanning Transmission Electron Microscopy,Energy Transfer,Electron Energy-Loss Spectroscopy
更新于2025-09-23 15:19:57
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Tuning the hybridization of local exciton and chargea??transfer states in highly efficient organic photovoltaic cells
摘要： Decreasing the energy loss is one of the most feasible ways to improve the efficiencies of organic photovoltaic (OPV) cells. Recent studies have suggested that non-radiative energy loss (ΔEnr) is the dominant factor that hinders further improvements in state-of-the-art OPV cells. However, there is no rational molecular design strategy for OPV materials with suppressed ΔEnr. In this work, taking molecular surface electrostatic potential (ESP) as a quantitative parameter, we establish a general relationship between chemical structure and intermolecular interactions. The results reveal that increasing the ESP difference between donor and acceptor will enhance the intermolecular interaction. In the OPV cells, the enhanced intermolecular interaction will increase the charge transfer (CT) state ratio in its hybridization with local exciton to facilitate the charge generation but simultaneously result in a larger ΔEnr. These results suggest that finely tuning the ESP of OPV materials is a feasible method to further improve the efficiencies of OPV cells.
关键词： hybridization,charge transfer state,intermolecular interaction,organic photovoltaic cells,non-radiative energy loss
更新于2025-09-23 15:19:57
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CoCl2 as film morphology controller for efficient planar CsPbIBr2 perovskite solar cells
摘要： High quality perovskite (PVK) film is quite important to reduce the energy loss (Eloss) and enhance the performance of planar CsPbIBr2 PVK solar cells (PSCs). In this work, 5% PbBr2 is substituted by CoCl2 in inorganic CsPbIBr2 PVK, acting as film morphology controller to slow down the crystallization process. It results in a dense and flat pinhole-free CsI(PbBr2)0.95(CoCl2)0.05 PVK film. Therefore, the trap state density is greatly reduced, which lead to reduce non-radiative recombination of carriers and Eloss, therefore, the open-circuit voltage (Voc) of the device is increased from 1.14V of control sample to 1.25V. The optimal photoelectric conversion efficiency (PCE) is enhanced to 10.43% relative to 6.93% of CsPbIBr2 PSCs. More importantly, the air stability of CsI(PbBr2)0.95(CoCl2)0.05 PSCs is greatly enhanced, which still maintain above 90% in the air of 25(cid:1) and RH=20% for 25 days without encapsulation. This work highlights the great effect of CoCl2 as a morphology controller on improving CsPbIBr2 film quality and device performance.
关键词： energy loss,inorganic perovskite solar cell,crystalline growth,charge transport,film quality
更新于2025-09-23 15:19:57
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Optimized Molecular Packing and Nonradiative Energy Loss Based on Terpolymer Methodology Combining Two Asymmetric Segments for High-Performance Polymer Solar Cells
摘要： In this work, a random terpolymer methodology combining two electron-rich units, asymmetric thienobenzodithiophene (TBD) and thieno[2,3-f]benzofuran (TBF) segments, is systematically investigated. The synergetic effect is embodied on the molecular packing and nanophase when copolymerization with 1,3-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione (BDD), producing an impressive power conversion efficiency (PCE) of 14.2% in IT-4F based NF-PSCs, which outperformed the corresponding D-A copolymers. The balanced aggregation and better interpenetrating network of the TBD50:IT-4F blend film can lead to mixing region exciton splitting and suppress carrier recombination, along with high yields of long-lived carriers. Moreover, the broad applicability of terpolymer methodology is successfully validated in most electron-deficient systems. Especially, TBD50/Y6-based device exhibits high PCE of 15.0% with a small energy loss (0.52 eV) enabled by the low non-radiative energy loss (0.22 eV), which are among the best values reported for polymers without using BDT unit to date. These results demonstrate an outstanding terpolymer approach with backbone engineering to raise the hope of achieving even higher PCEs and to enrich organic photovoltaic materials reservoir.
关键词： asymmetrical structure,microstructure,random terpolymer,nonfullerene solar cell,non-radiative energy loss,power conversion efficiency
更新于2025-09-23 15:19:57
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Localized Surface Plasmon Resonance-Induced Welding of Gold Nanotriangles and the Local Plasmonic Properties for Multicolor Sensing and Light-Harvesting Applications
摘要： The excitation of localized surface plasmon resonance in gold nanotriangles by continuous light illumination triggered the welding of two adjacent nanotriangles into one nanoparticle. The facing localized surface plasmon resonance generated at the corners of the gold nanotriangles facilitated welding of the nanotriangles, in which electromagnetically seamless bonding was formed. We examined the scanning transmission electron microscopy-electron energy loss spectra of the obtained nanostructure and confirmed the generation of a localized plasmon mode at the bonding spot with an energy of 2.3 eV, which did not appear in the two adjacent gold nanotriangles without bonding. The experimental electron energy loss spectra and maps were supported by the simulation data calculated using the boundary element method. An electromagnetically continuous nanostructure was successfully constructed by a site-selective welding method in this work, resulting in modulation of the localized surface plasmon resonance in nanoparticles, including the localized spots, resonant wavelength and enhancement factor. The generation of a localized surface plasmon resonance mode by welding of nanoparticles can enable multicolor sensing and light harvesting applications.
关键词： plasmon mode,site-selective welding,nanoparticle,electron energy loss spectroscopy,localized surface plasmon resonance,gold nanotriangle
更新于2025-09-23 15:19:57
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Tents, Chairs, Tacos, Kites, and Rods: Shapes and Plasmonic Properties of Singly Twinned Magnesium Nanoparticles
摘要： Nanostructures of some metals can sustain light-driven electron oscillations called localized surface plasmon resonances, or LSPRs, that give rise to absorption, scattering, and local electric field enhancement. Their resonant frequency is dictated by the nanoparticle (NP) shape and size, fueling much research geared towards discovery and control of new structures. LSPR properties also depend on composition; traditional, rare and expensive noble metals (Ag, Au) are increasingly eclipsed by earth-abundant alternatives, with Mg being an exciting candidate capable of sustaining resonances across the ultraviolet, visible, and near-infrared spectral ranges. Here, we report numerical predictions and experimental verifications of a set of shapes based on Mg NPs displaying various twinning patterns including (10 1), (10 2), (10 3) and (11 1), that create tent, chair, taco and kite-shaped NPs, respectively. These are strikingly different from what is obtained for typical plasmonic metals because Mg crystallizes in a hexagonal close packed structure, as opposed to the cubic Al, Cu, Ag, and Au. A numerical survey of the optical response of the various structures, as well as the effect of size and aspect ratio, reveals their rich array of resonances, which are supported by single particle optical scattering experiments. Further, corresponding numerical and experimental studies of the near-field plasmon distribution via scanning transmission electron microscopy electron-energy loss spectroscopy unravels a mode nature and distribution that are unlike those of either hexagonal plates or cylindrical rods. These NPs, made from earth-abundant Mg, provide interesting ways to control light at the nanoscale across the ultraviolet, visible, and near-infrared spectral ranges.
关键词： nanoplasmonics,nanoparticle shape,magnesium nanoparticles,localized surface plasmon resonance,electron-energy loss spectroscopy,Wulff construction
更新于2025-09-23 15:19:57
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Delocalization boosts charge separation in organic solar cells
摘要： Organic solar cells (OSCs) utilizing π-conjugated polymers have attracted widespread interest over the past three decades because of their potential advantages, including low weight, thin film flexibility, and low-cost manufacturing. However, their power conversion efficiency (PCE) has been far below that of inorganic analogs. Geminate recombination of charge transfer excitons is a major loss process in OSCs. This paper reviews our recent progress in using transient absorption spectroscopy to understand geminate recombination in bulk heterojunction OSCs, including the impact of polymer crystallinity on charge generation and dissociation mechanisms in nonfullerene acceptor-based OSCs. The first example of a high PCE with a small photon energy loss is also presented. The importance of delocalization of the charge wave function to suppress geminate recombination is highlighted by this focus review.
关键词： Polymer crystallinity,Power conversion efficiency,Organic solar cells,Transient absorption spectroscopy,Dissociation mechanisms,Photon energy loss,π-conjugated polymers,Charge generation,Nonfullerene acceptor,Geminate recombination
更新于2025-09-23 15:19:57