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Effects of interfacial energy level alignment on carrier dynamics and photovoltaic performance of inverted perovskite solar cells
摘要： Metal doping is an efficient method for optimizing NiOx as hole transport material in the inverted perovskite solar cells, which can contribute to the optimization of the interfacial energy level alignment, while the underlying influencing mechanism on the charge carrier dynamics and device performance needs to be further elucidated. In this work, NiOx films with modulated energy levels are obtained via Li doping and examined by ultraviolet photoelectron spectrometer. The effects of the energy level alignment of NiOx on the carrier transfer and recombination dynamics are elucidated by transient photovoltage/photocurrent and transient fluorescence dynamics. The Li doping can significantly shift the valence band of NiOx downward, and the 4% Li content endows NiOx with the optimal energy level matching with perovskite and the best charge separation/transfer ability, which can be confirmed through the photoluminescence results. The corresponding device possesses superior photovoltaic parameters with the champion power conversion efficiency of 17.34%, 37% higher than device based on pure NiOx. The results highlight that proper metal doping can optimize the energy level of the hole transport material to well match the perovskite, thus efficiently promoting charge separation and inhibiting charge recombination, which leads to the enhancement of the device performances.
关键词： Li-doped NiOx,Inverted perovskite solar cell,Charge transport/recombination dynamics,Energy level alignment
更新于2025-09-19 17:13:59
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Charge Transport and Photovoltaic Properties of Conjugated Polymer PTB7:PC71BM Based Solar Cells
摘要： We investigate the charge transport in organic solar cells based on PTB7:PC71BM by measuring the J (V) characteristics at different temperatures (140–325 K). In dark, two models dominate the transport. The Ohmic law overcomes for the low applied low voltages, and for high voltages the trapped charge limited current governs the transport with an average total concentration of trap around 5.62 × 1015 cm?3. At higher voltages there is evidence of an electrode-to-bulk limited transition, with conductivity dominated by the Poole–Frenkel effect. The photovoltaic conversion properties of the junction were also studied by carrying out the J–V measurements at room temperature under illumination of 100 mW/cm2 and a power conversion efficiency of 6.49% has been achieved. the other cell parameters, the short-circuit current density JSC, the open circuit voltage VOC and de fill factor FF, were found to be 12.87 mA/cm2, 0.77 V and 0.65 respectively. These values were compared with other organic solar cells found in literature.
关键词： Charge transport,Photovoltaics,Organic materials,Trap density
更新于2025-09-19 17:13:59
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Nitrogen-doped CQDs to enhance the power conversion efficiency of perovskite solar cells via surface passivation
摘要： In this study, nitrogen doped CQDs (N-CQDs), as a novel additive, were successfully synthesized and characterized by XPS, TEM and UVeVis spectrometry techniques. Importantly, we introduced N-CQDs in CH3NH3PbI3 solar cells. The results indicated that nonradiative charge back recombination decreased and the trap states in the absorber layer were passivated when N-CQDs was used an additive in CH3NH3PbI3 solution. Additionally, the morphological characterization results indicated that the crystallization problems and defects on perovskite surfaces can be easily resolved by N-CQDs additive in perovskite solution. A significant improvement in power conversion efficiency at a yield of 14% is achieved by doping of 3 vol% of N-CQDs, thanks to enhancement of charge transport properties due to the morphological and electrical changes. Herein, we propose an effective and novel additive for the fabrication of high efficiency perovskite solar cell, which can be seen that this method is simple.
关键词： Film coverage,N-CQDs,Perovskite solar cells,Charge transport properties
更新于2025-09-19 17:13:59
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Honeycomb-shaped charge collecting electrodes for dipole-assisted back-contact perovskite solar cells
摘要： Dipole-field-assisted charge-transporting-material-free lead halide perovskite solar cells (PSCs) using a back-contact configuration feature intrinsic advantages, such as no parasitic light absorption and high architectural defect tolerance. Herein, a newly designed, highly defect tolerant honeycomb-shaped back-contact (HBC) electrode was incorporated into dipole-field-assisted-back-contact PSCs, aiming to optimize the charge transport distance before being collected by the electrodes. HBC-PSCs with three feature sizes were fabricated in order to understand the effect of charge transport distance on device performance. The photovoltaic performance of HBC-PSCs correlates inversely proportional to the feature sizes. The mechanism behind the performance difference is elucidated via a detailed analysis through device current voltage characterization, transient photovoltage decay measurement and photocurrent mapping. A comprehensive comparison between honeycomb-shaped and interdigitated finger back-contact electrodes for PSCs is also conducted.
关键词： surface modification,charge transport distance,perovskite solar cells,honeycomb-shaped back-contact electrodes
更新于2025-09-19 17:13:59
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Enhancing Charge Carrier Delocalization in Perovskite Quantum Dot Solids with Energetically Aligned Conjugated Capping Ligands
摘要： Compared to bulk perovskites, charge transport in perovskite quantum dot (PQD) solids is limited. To address this issue, energetically aligned capping ligands were used to prepare methylammonium lead bromide (MAPbBr3) PQDs towards enhancing surface charge carrier density in PQD solids. Trans-cinnamic acid (TCA) and its derivates, functionalized with electron-donating or electron-withdrawing groups to modulate energy levels, are used as passivating exciton-delocalizing ligands (EDLs) to decrease the energy gap with respect to the PQD core. 3,3-diphenylpropylamine (DPPA) ligand is shown to stabilize EDLs on the PQD surface through π-π stacking intermolecular interaction, mitigating charge trapping and non-radiative decay. Passivation using EDLs in combination with DPPA increases the photoluminescence (PL) quantum yield (QY) (90%), photoconductivity, extraction, mobility, transport time, and lifetime of charge carriers in PQD solids. Prototype PQD-based light-emitting diodes (LEDs) were demonstrated with a low turn-on voltage of 2.5 V.
关键词： charge transport,light-emitting diodes,capping ligands,perovskite quantum dots,photoluminescence
更新于2025-09-19 17:13:59
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Unraveling the Structure-Property Relationship of Molecular Hole Transporting Materials for Perovskite Solar Cells
摘要： Clarifying the structural basis and microscopic mechanism lying behind electronic properties of molecular semiconductors is of paramount importance in further materials design to enhance the performance of perovskite solar cells. In this paper, three conjugated quasi-linear segments of 9,9-dimethyl-9H-fluorene, 9,9-dimethyl-2,7-diphenyl-9H-fluorene, and 2,6-diphenyldithieno[3,2-b:2',3'-d]thiophene are end-capped with two bis(4-methoxyphenyl)amino groups for structurally simple molecular semiconductors Z1, Z2, and Z3, which crystalline in the monoclinic, triclinic, and monoclinic space groups, respectively. The modes and energies of intermolecular noncovalent interactions in various closely packed dimers extracted from single crystals are computed based on the quantum theory of atoms in molecules and energy decomposition analysis. Transfer integrals, reorganization energies, and center-of-mass distances in these dimers as well as band structures of single crystals are also calculated to define the theoretical limit of hole transport and microscopic transport pictures. Joint X-ray diffraction and space-charge limiting current measurements on solution-deposited films suggest the dominant role of crystallinity in thin film hole mobility. Photoelectron spectroscopy and photoluminescence measurements show that an enhanced interfacial interaction between perovskite and Z3 could attenuate the adverse impact of reducing the energetic driving force of hole extraction. Our comparative studies show that molecular semiconductor Z3 with a properly aligned HOMO energy level and a high thin film mobility can be employed for efficient perovskite solar cells, achieving a good power conversion efficiency of 20.84%, which is even higher than that of 20.42% for spiro-OMeTAD control.
关键词： charge recombination,perovskite solar cell,molecular crystal,noncovalent interaction,crystallinity,charge transport,organic semiconductor
更新于2025-09-16 10:30:52
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Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells
摘要： The study of p-type dye sensitized solar cells (p-DSCs) is appealing but challenging. Although the devices have been studied for 20 years, light conversion efficiency is lag far behind those of n-DSCs. Very recently, on the basis of a core-shell structure, a novel solid-state p-DSC (p-ssDSCs) has been fabricated, which showed great enhancement in open-circuit voltage and dye regeneration rate. To further improve the performance of such devices, charge diffusion, recombination process and the main limiting factors have to be understood. In the present paper, core-shell p-ssDSCs with ZnO as an electron conductor were fabricated by atomic layer deposition. The charge transport time was determined to be ca. 0.1 ms, which is about 2 orders of magnitude faster than those of typical liquid devices with I-/I3- as a redox mediator. As a consequence, the devices exhibit the highest reported apparent charge diffusion coefficient (Dapp) among p-DSCs. It is ascribed to an electron limiting diffusion process by the ambipolar diffusion model, suggesting a different charge transport determining mechanism in contrast to liquid p-DSCs. The charge recombination rate is 1-2 orders of magnitude slower than its charge transport time, resulting in that the estimated charge collection efficiency is near unity. Detailed analysis of the incident photon-to-electron conversion efficiency suggests, that the energy conversion efficiency in these p-ssDSCs is currently limited by a large fraction of dyes that is not fully electrically connected in the device.
关键词： solid-state,charge recombination,p-type dye sensitized solar cells,dye utilization fraction,charge transport
更新于2025-09-16 10:30:52
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Influence of active layer thickness on photovoltaic performance of PTB7:PC70BM bulk heterojunction solar cell
摘要： In this paper, we studied the effect of active layer thickness on the photovoltaic performance of inverted bulk heterojunction (BHJ) organic solar cell (OSC). The capacitance-voltage (C–V), dark current-voltage (I–V) and impedance spectroscopy (IS) analysis were carried out to explain the active layer thickness dependence on the photovoltaic performance. The OSC with an active layer thickness of 150 nm achieved the best power conversion efficiency (PCE) of 5.87%, while the OSC of 200 nm active layer thickness yielded the worst PCE. Reduction in the fill factor (FF) was the main reason for the reduction in the PCE at large active layer thickness. The dark I–V analysis revealed large defect density for the OSC with active layer thickness of 200 nm, which raised the charge recombination and leakage current and consequently reduced the FF. IS analysis predicted that the charge transport became the serious limitations for the OSC with 200 nm thick active layer, which can be attributed to the weakening of electric field as well as creation of field-free regions. It mainly caused a drastic drop in the fill factor by reducing the charge collection efficiency, consequently deteriorated the photovoltaic performance.
关键词： Charge recombination,Bulk heterojunction solar cell,Ideality factor,Photovoltaic performance,Charge transport resistance,Leakage current
更新于2025-09-16 10:30:52
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Critical Role of Polymer Aggregation and Miscibility in Nonfullerenea??Based Organic Photovoltaics
摘要： Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature-dependent aggregation, namely PffBT4T-2OD [poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″′-di(2-octyldodecyl)-2,2′;5′,2″;5″,2″′-quaterthiophen-5,5-diyl)], also known as PCE-11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O-IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O-IDTBR are a strong function of the chemical composition, leading to different donor–acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid–liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor–acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor–acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.
关键词： nonfullerene acceptors,charge transport,morphology,charge generation,polymer aggregation
更新于2025-09-16 10:30:52
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Positive effects of side-chain fluorination and polymer additive SBS on the enhanced performance of asymmetric-indenothiophene-based polymer solar cells
摘要： Two new D-A type photovoltaic polymers, namely PITPh-DfQx and PITPhf-DfQx, based on asymmetric indenothiophene (IT) donor units with alkoxyphenyl or fluoroalkoxyphenyl substitutes were designed and synthesized. Effects of the fluorine substitution in the asymmetric IT donor units on the electronic structure, ordering structure, photovoltaic properties, and charge generation and recombination dynamics were investigated. It is found that side-chain fluorination in the asymmetric donor units of the D-A polymers endowed the relative polymers with a deeper HOMO level, higher and more balanced charge mobilites, increased charge dissociation efficiency and reduced bimolecular recombination. As a result, the bulk heterojunction solar cell based on the blend film of PITPhf-DfQx and PC71BM demonstrated an efficiency of 6.10%, whereas the cell efficiency based on PITPh-DfQx was only 3.00%. In addition, a triblock copolymer, poly(styrene-block-butadiene-block-styrene) (SBS), was employed for the first time as a polymer additive into the active layers based on PITPh-DfQx/PC71BM and PITPhf-DfQx/PC71BM devices to promote donor crystallization and tune the extent of phase separation between the donor and acceptor. The presence of SBS obviously improved the molecule packing and induced the crystallization of the two polymers, giving rise to a better phase separation due to enhanced aggregation effect of photovoltaic polymers. Therefore, with a small addition of SBS, the optimal PCE was further increased from 6.10% to 6.60% for PITPhf-DfQx based device and from 3.00% to 5.50% for PITPh-DfQx based device. The positive effects of SBS additive on the performance of photovoltaic polymer/fullerene BHJ solar cells provide a new strategy for developing high performance polymer solar cells.
关键词： Morphology,Polymer additive SBS,Charge transport,Side-chain fluorination,Polymer solar cells,Asymmetric-indenothiophene
更新于2025-09-16 10:30:52