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Elucidating the effects of guest-host energy level alignment on charge transport in phosphorescent OLEDs
摘要： The correct choice of guest and host molecules in the light-emitting layer is essential for developing high performance phosphorescent organic light emitting devices. However, the effects of the energy level alignment between the guest and the host are yet to be fully elucidated. In this Letter, we use kinetic Monte Carlo simulations to investigate guest-host systems in which the energy gap of the guest and host is fixed, and only the relative energies of the ionization potential/electron affinity are changed to elucidate their effect on charge transport. It was determined that the mobility balance in the blend was sensitive to the energy level alignment, allowing balanced active layer mobility to be achieved despite the hole and electron mobilities being different by around one order of magnitude. It was also found that the mobility of the faster carrier was more sensitive to the energy level alignment than that of the slower carrier due to reduced slower carrier thermalization under deep charge trapping on the guest.
关键词： guest-host energy level alignment,phosphorescent OLEDs,kinetic Monte Carlo simulations,charge transport
更新于2025-09-12 10:27:22
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Self-assembled naphthalimide derivatives as an efficient and low-cost electron extraction layer for n-i-p perovskite solar cells
摘要： Based on self-assembly, novel electron extraction layers (EELs) composed of naphthalimide (NPI) derivatives are constructed for application in n-i-p perovskite solar cells. Upon molecular energy level modulation, the power conversion efficiencies have been largely improved from 5.4% to 16%. Such low-cost and highly regulable EELs are promising for future commercial applications.
关键词： electron extraction layer,molecular energy level modulation,perovskite solar cells,Self-assembled naphthalimide derivatives
更新于2025-09-12 10:27:22
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Spiro‐Linked Molecular Hole‐Transport Materials for Highly Efficient Inverted Perovskite Solar Cells
摘要： Spiro-linked compounds have been used as benchmark hole-transport materials (HTMs) for the construction of efficient normal architecture (n-i-p) perovskite solar cells (PSCs). However, the heavy reliance on the use of dopants not only complicates the device fabrication but imposes long-term stability concern of the devices. Herein, it is reported that solution-processed dopant-free spiro molecules can serve as superior HTMs to fabricate efficient inverted (p-i-n) PSCs. Rational choice of orthogonal solvent allows us to solution deposit uniform and pinhole-free perovskite films without compromising the hole-extraction capability of the spiro-based interface layers. To illustrate the generality of the strategy, three spiro-linked molecules are investigated side by side as HTMs in one-step solution-processed CH3NH3PbI3 PSCs. Due to the favored energy-level alignment and high hole mobility, solar cells based on the HTM of spiro-TTB yield a high efficiency of 18.38% with open-circuit voltages (VOC) up to 1.09 V. These results suggest that small molecular HTMs commonly developed for normal structure devices can be of great potential to fabricate cost-effective and highly efficient inverted PSCs.
关键词： inverted solar cells,energy-level alignments,spiro-linked compounds,perovskites
更新于2025-09-12 10:27:22
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Direct Observation of Conductive Polymer Induced Inversion Layer in n‐Si and Correlation to Solar Cell Performance
摘要： Heterojunctions formed by ultrathin conductive polymer [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)—PEDOT:PSS] films and n-type crystalline silicon are investigated by photoelectron spectroscopy. Large shifts of Si 2p core levels upon PEDOT:PSS deposition provide evidence that a dopant-free p–n junction, i.e., an inversion layer, is formed within Si. Among the investigated PEDOT:PSS formulations, the largest induced band bending within Si (0.71 eV) is found for PH1000 (high PEDOT content) combined with a wetting agent and the solvent additive dimethyl sulfoxide (DMSO). Without DMSO, the induced band bending is reduced, as is also the case with a PEDOT:PSS formulation with higher PSS content. The interfacial energy level alignment correlates well with the characteristics of PEDOT:PSS/n-Si solar cells, where high polymer conductivity and sufficient Si-passivation are also required to achieve high power conversion efficiency.
关键词： core level shifts,band bending,PEDOT:PSS/Si solar cell,energy level alignment,inversion layer
更新于2025-09-11 14:15:04
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Electron Transporting Bilayer of SnO <sub/>2</sub> and TiO <sub/>2</sub> Nanocolloid Enables Highly Efficient Planar Perovskite Solar Cells
摘要： Here, we applied the commercially accessible SnO2 and home-made TiO2 NPs as a combined electron transporting bilayer (ETBL) to achieve a highly efficient planar perovskite solar cell (PSC). The formed cascade-aligned energy levels from the proper stacking of SnO2 and TiO2 layers and the excellent defect-passivation ability of TiO2, SnO2/TiO2 ETBLs effectively reduced energy loss and inhibited defects formation both at the ETL/perovskite interface and within the bulk of perovskite layer as revealed by a comprehensive analysis of photoelectric characteristic analysis, including ultraviolet photoelectron spectroscopy, photoluminescence and electrochemical impedance spectroscopy. Consequently, the PSC devices acquired a high PCE of 20.50% with a Voc of 1.10 V, a Jsc of 24.2 mA/cm2 and an FF of 77%, which are superior to the values of the control device based on single SnO2 layer with a PCE of 18.09% (a 13.3% boosting on PCE). Moreover, there was no degradation after 49 days, indicating the great stability after adding TiO2 layer. Our work demonstrates that the cascaded alignment of energy levels between the electrode and perovskite layer by ETBLs could be an effective approach to improve the photovoltaic performance of the PSCs with excellent long-term stability.
关键词： electron transporting bilayer,perovskite solar cells,SnO2 nanoparticles,TiO2 nanoparticles,cascade-aligned energy level
更新于2025-09-11 14:15:04
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Efficient non-fullerene polymer solar cells enabled by side-chain conjugated thieno[3,4-c]pyrrole-4,6-dione-based polymer and small molecular acceptors
摘要： The application of non-fullerene (NF) acceptors in bulk-heterojunction (BHJ) polymer solar cells (PSCs) is a promising approach to overcome the inherent drawbacks of fullerene derivatives-based acceptors. In PSCs, complementary absorption as well as matched molecular energy levels between the low bandgap acceptor-donor-acceptor (A-D-A) small molecular acceptor and medium/wide bandgap polymer donor is crucial to achieve high power conversion efficiency (PCE). Alternating polymers based on benzodithiophene (BDT) electron-donating segment and thieno[3,4-c]pyrrole-4,6-dione (TPD) electron-withdrawing segment own medium bandgap and low-lying highest occupied molecular orbital (HOMO) energy level, leading to presentable photovoltaic properties with fullerene derivatives. To probe into the performances of TPD-based polymers in NF-PSCs, two TPD-based polymers containing alkoxy or alkylthienyl modified benzo[1,2-b:4,5-b′]dithiophene (BDT) were synthesized and adopted as electron-donors and blended with A-D-A-type electron-acceptor 2,2′-[[6,6,12,12-tetrakis(4-hexylphenyl)-s-indacenodithieno[3,2-b]thiophene]methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis(propanedinitrile) (ITIC) to fabricate the corresponding photovoltaic devices. The two-dimensional conjugated polymer PBDTT-TPD shows enhanced extinction coefficient, deeper HOMO energy level and better hole transport performance, resulting in improved PCE of 6.17%. To further boost the performances of the polymers, a small molecular acceptor 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl) bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) with down-shifted energy level was also used to blend with the two polymers in PSCs. Despite the open-circuit voltage (VOC) of the PBDTT-TPD:IDIC-based device is slightly decreased, the short-circuit current density (JSC) and fill factor (FF) are simultaneously improved, yielding an promising PCE of 7.15%. These results indicate that two-dimensional conjugated TPD-based polymers can be potential application as medium bandgap polymeric donor to match with small molecular acceptors having suitable molecular energy levels to get high efficiency in PSCs.
关键词： Non-fullerene acceptors,Thieno[3,4-c]pyrrole-4,6-dione,Energy level offsets,Polymer solar cells,Thermal annealing
更新于2025-09-11 14:15:04
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Tuning the molecular packing and energy level of fullerene acceptors for polymer solar cells
摘要： Fullerenes are considered to be promising acceptor materials for fabrication of bulk-heterojunction polymer solar cells (PSCs) due to their excellent physical and chemical properties. Herein, two novel fullerene derivatives with different specific functional groups, 2-benzylthiophene-C60 bis-adduct (BTCBA) and 2-(4-methoxybenzyl)thiophene-C60 bis-adduct (MBTCBA), were synthesized and utilized as the acceptors for PSCs with the purpose of investigating the influence of the fullerene derivative substituents on the device performance. Compared with BTCBA, MBTCBA exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level due to the electron donating properties of the 2-(4-methoxybenzyl)thiophene functional group. Meanwhile, the appropriate intermolecular interaction of MBTCBA molecules promotes favorable nanophase separation of the P3HT/MBTCBA based blending film, resulting in higher electron mobility. Therefore, the PSCs incorporating P3HT as donor and MBTCBA as acceptor yield a power conversion efficiency (PCE) of 5.29% with an open-circuit voltage (VOC) of 0.81 V, which is obviously higher than that of BTCBA (3.54%) and PCBM (3.76%) based devices. Our work proves that the PSCs performance can be readily improved by modification of fullerene acceptors using electron donating group, tuning the LUMO energy level and the molecular packing behavior.
关键词： Bis-adduct fullerene derivatives,Fullerenes,LUMO energy level,Molecular packing,Polymer solar cells
更新于2025-09-11 14:15:04
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π-Conjugated small molecules enable efficient perovskite growth and charge-extraction for high-performance photovoltaic devices
摘要： A π-conjugated small molecule N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) is introduced into a poly (bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) hole transport layer in inverted perovskite solar cells (PSCs). The NPB doping induces better perovskite crystal growth owing to a strong π-π interaction with PTAA and cation-π interactions with CH3NH3+ (MA+). In addition, NPB doping not only improves the wettability of PTAA and regulates the perovskite crystallization to achieve a larger grain size, but also moves the valence band energy of the hole transport layer closer to the perovskite layer. Consequently, the fabricated PSCs delivered a power conversion efficiency (PCE) of 20.15%, with a short-circuit current density (JSC) of 22.60 mA/cm2 and open-circuit voltage (VOC) of 1.14 V. This outcome indicates that PTAA:NPB composite materials present great potential for fabricating high-performance PSCs.
关键词： Energy level alignment,Charge extraction,π-conjugated molecule
更新于2025-09-11 14:15:04
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Minimizing Voltage Loss in Efficient All-inorganic CsPbI2Br Perovskite Solar Cells through Energy Level Alignment
摘要： All-inorganic CsPbI2Br, prized for its strong stability against thermal aging and light soaking, has attracted intensive attention. However, a large energy loss results from the serious energy level offset of 1.05 eV between CsPbI2Br and Spiro-MeOTAD, hindering further efficiency improvement of PSCs. To address this issue, a moderate energy level (CsPbI2Br)1-x(CsPbI3)x layer has been introduced at the interface between CsPbI2Br and Spiro-MeOTAD to form graded energy level alignment. The interpolation of which has offered the energy level gradient for reducing the resistance of hole transport. Correspondingly, the energy level tailoring has minimized the energy loss and a remarkable VOC improved from 1.12 V to 1.32 V, which is one of the highest values for CsPbI2Br based solar cells. A relatively good thermal stability has also been validated. These good performances indicate that setting an intermediate energy level alignment will be a potential strategy for idealized device architecture to minimize energy loss.
关键词： Thermal Stability,Voltage Loss,Energy Level Alignment,All-inorganic CsPbI2Br,Perovskite Solar Cells
更新于2025-09-11 14:15:04
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ions
摘要： Laser-produced Sn plasma sources are used to generate extreme ultraviolet light in state-of-the-art nanolithography. An ultraviolet and optical spectrum is measured from a droplet-based laser-produced Sn plasma, with a spectrograph covering the range 200–800 nm. This spectrum contains hundreds of spectral lines from lowly charged tin ions Sn1+?Sn4+ of which a major fraction was hitherto unidenti?ed. We present and identify a selected class of lines belonging to the quasi-one-electron, Ag-like ([Kr]4d 10 nl electronic con?guration), Sn3+ ion, linking the optical lines to a speci?c charge state by means of a masking technique. These line identi?cations are made with iterative guidance from COWAN code calculations. Of the 53 lines attributed to Sn3+, some 20 were identi?ed from previously known energy levels, and 33 lines are used to determine previously unknown level energies of 13 electronic con?gurations, i.e., 7p, (7, 8)d, (5, 6)f , (6–8)g, (6–8)h, (7, 8)i. The consistency of the level energy determination is veri?ed by the quantum-defect scaling procedure. The ionization limit of Sn3+ is con?rmed and re?ned to 328 908.4 cm?1, with an uncertainty of 2.1 cm?1. The relativistic Fock-space coupled-cluster (FSCC) calculations of the measured level energies are generally in good agreement with experiment but fail to reproduce the anomalous behavior of the 5d 2D and nf 2F terms. By combining the strengths of the FSCC calculations, COWAN code calculations, and con?guration interaction many-body perturbation theory, this behavior is shown to arise from interactions with doubly excited con?gurations.
关键词： Sn3+ ions,energy-level structure,nanolithography,laser-produced plasma,extreme ultraviolet light
更新于2025-09-09 09:28:46