Efficient Electron Extraction Research Articles

Efficient charge transport in a solid electrolyte with percolated Pt for solid-state fiber dye-sensitized solar cells

Percolation effect introduced solid-state electrolyte is fabricated by metal sputtering process on the surface of Li-TFSI film. The percolation effect could provide efficient electron extraction through the solid electrolyte surface.

Atomic Layer Deposited ZnO–SnO2 Electron Transport Bilayer for Wide‐Bandgap Perovskite Solar Cells

High‐quality electron transport layer (ETL) is a prerequisite for high‐performance wide‐bandgap mixed‐halide perovskite solar cells (PSCs), which is critical for efficient perovskite/silicon tandem solar cells. Herein, an atomic layer deposited ZnO–SnO2 bilayer ETL for wide‐bandgap PSCs is reported, featuring a high uniformity and conformality over a large area. The ZnO–SnO2 bilayer shows a matched band alignment with wide‐bandgap perovskite for efficient electron extraction and transport, with a lower nonradiative recombination. As a result, a champion power conversion efficiency of 18.1% is achieved on the ZnO–SnO2 bilayer‐based wide‐bandgap PSCs featuring an ultrahigh open‐circuit voltage (Voc) of 1.233 V, which is the highest value for wide‐bandgap PSCs without any surface passivation. In addition, the atomic layer deposition ZnO–SnO2 bilayer exhibits very good surface passivation and conformality on crystalline silicon surfaces, which makes it attractive to be applied for perovskite/silicon tandem solar cells with a higher Voc and textured surfaces.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Efficient Hot Electron Capture in CuPc/MoSe2 Heterostructure Assisted by Intersystem Crossing.

Efficient hot electron extraction is a promising approach to develop photovoltaic devices that exceed the Shockley-Queisser limit. However, experimental evidence of hot electron harvesting employing an organic-inorganic interface is still elusive. Here, we reveal the hot electron dynamics at a CuPc/MoSe2 interface using steady-state spectroscopy and transient absorption spectroscopy. A hot electron transfer efficiency of greater than 78% from MoSe2 to CuPc is observed, comparable to that achieved in quantum dot hybrid systems. The mechanism is proposed as follows: the photogenerated hot electrons in MoSe2 transfer to CuPc and form singlet charge transfer states, which subsequently transform into triplet charge transfer states assisted by the rapid intersystem crossing, inhibiting back-donation of electrons and facilitating exciton dissociation into CuPc polarons with a nanosecond lifetime. Our results demonstrate that the intersystem crossing of the hybrid electronic state at organic-inorganic interfaces may serve as a scheme to enable efficient hot electron extraction in photovoltaic devices.

Strategic Approach for Frustrating Charge Recombination of Perovskite Solar Cells in Low-Intensity Indoor Light: Insertion of Polar Small Molecules at the Interface of the Electron Transport Layer

In this study, we propose a strategic interface engineering method for optimizing the power density and power conversion efficiency (PCE) of perovskite solar cells (PVSCs) under low-intensity indoor light conditions. The insertion of a polar bathocuproine (BCP) layer at the electron transport interface significantly improved the photovoltaic properties, in particular, the fill factor and open circuit voltage, in a low-intensity light environment. Based on the systemic characterizations of surface trap states and carrier dynamics using Kelvin probe force microscopy, we revealed that BCP facilitated efficient charge carrier separation and electron extraction under low-intensity light illumination due to surface passivation and dipole-induced suppressed charge recombination. The beneficial role of BCP enabled excellent indoor PCEs of 27.04 and 35.45% under low-intensity light-emitting diode and halogen lights, respectively. Modification of the electron transport layer interface using polar molecules is a simple but highly effective method for optimizing the indoor performance of PVSCs.

Simulation and Optimization of FAPbI3 Perovskite Solar Cells with a BaTiO3 Layer for Efficiency Enhancement.

Since the addition of BaTiO3 in perovskite solar cells (PSCs) provides a more energetically favorable transport route for electrons, resulting in more efficient charge separation and electron extraction, in this work we experimentally prepared such a PSC and used a modeling approach to point out which simulation parameters have an influence on PSC characteristics and how they can be improved. We added a layer of BaTiO3 onto the TiO2 electron transport layer and prepared a PSC, which had an FTO/TiO2/BaTiO3/FAPbI3/spiro-OMeTAD/Au architecture with a power conversion efficiency (PCE) of 11%. Further, we used the simulation program SCAPS-1D to investigate and optimize the device parameters (thickness of the BaTiO3 and absorber layers, doping, and defect concentration) resulting in devices with PCEs reaching up to 15%, and even up to 20% if we assume an ideal structure with no interlayer defects. Our experimental findings and simulations in this paper highlight the promising interplay of multilayer TiO2/BaTiO3 ETLs for potential future applications in PSCs.

A General Large-Scale Fabrication of Tin Oxide with Interfacial Engineering via Trichloropropylsilane for Hysteresis-Free MAPbI3 Perovskite Solar Cells Exceeding 20% PCE

Abstract We demonstrate a facile chemical bath deposition (CBD) of SnO2 films as excellent ETLs using a low temperature method (70 °C). The vacuum drying treatment and trichloropropylsilane (C3H7Cl3Si, Cl-Si) are employed for surface modification on SnO2 films due to the hygroscopicity of most metal oxides. The results reveal that the water molecules adsorbed on the CBD-SnO2 films can be desorbed by vacuum drying, and the hydrolysis products of Cl-Si can bond to SnO2 films through hydroxyl groups. Thus, the hydrophobicity of CBD-SnO2 is enhanced by employing the Cl-Si treatment, which is beneficial to improve the crystallinity of MAPbI3. The Cl-Si modified SnO2 films exhibit efficient electron extraction and hole blocking ability due to the higher electronic conduction band energy level than the pristine SnO2. Consequently, the MAPbI3 PSCs based on the hydrophobic Cl-Si/SnO2 exhibit a high PCE of 20.12% with low hysteresis, retaining 80% of the initial PCE after 500 h without any encapsulation at ambient condition. The 5 × 5 cm2 PSC modules prepared with this strategy achieve 15.24% efficiency (14.44% at forward scanning) with an aperture area of 10 cm2.

Surface modification of CsPbI2Br for improved performance of inorganic perovskite solar cells

Degradation of halide perovskite materials upon ambient exposure is one of the major challenge for their applications. Inorganic perovskite materials (such as CsPbI 2 Br) have emerged as potential candidate for stable perovskite optoelectronic applications in recent years owing to their appropriate bandgap and high thermal stability. However, the fabrication of high quality CsPbI 2 Br absorber layer is the main challenge to achieve highly efficient perovskite solar cells (PSCs). Herein, we report a strategy for the surface modification of CsPbI 2 Br layer via the treatment with isopropanol. The modified CsPbI 2 Br absorber layer has energetically more favorable band alignment with the C 60 which facilitates the efficient charge transfer and mitigate the energy loss at CsPbI 2 Br/C 60 interfaces. The inorganic PSCs with the architecture of ITO/NiO x /CsPbI 2 Br/C 60 /Cu showed open-circuit voltage (V OC ) of 1.13 V and 30% improvement in the power conversion efficiency (PCE). Moreover, the devices exhibit less hysteresis index and excellent stability with no sign of degradation for 160 h. • A modified post synthesis treatment of CsPbI 2 Br films was employed using isopropanol (IPA). • The CsPbI 2 Br treated film showed more favorable energetics for efficient electron extraction. • IPA treated device exhibited a 30% improvement in PCE with less hysteresis index when compared with devices without treatment.

Qualified interlayer modifier for organic solar cells with optimized interfacial topography and boosted efficiency based on biomass-derived acid

The cathode interlayer modification is crucial for the performance of organic solar cells (OSCs), which ensures an efficient electron extraction. However, the research progress of the cathode interlayer is seriously lagging behind, compared with the emerging of OSCs. In this research, three different biomass-derived acid, oxalic acid, azelaic acid and tannic acid, are investigated as the modifiers for the PDIN cathode interlayer of the non-fullerene acceptor based OSCs. The best performance is obtained via the modification of oxalic acid, due to its small conjugated molecule structure. It improves the cathode interlayer quality without disrupting the intermolecular stacking of PDIN. After the modification of oxalic acid, the energy barrier between the active layer and the cathode interlayer is reduced and the carrier recombination is suppressed. It helps the formation of a good ohmic contact and enhances the electron collection. Therefore, the average power conversion efficiency increases from 17.61% of the control device to 18.28%, with a champion efficiency of 18.43%. This research first demonstrates the application of biomass-derived acid in the cathode interlayer modification. It offers a novel strategy to achieve high-efficient cathode interlayer for OSCs using biomaterials.

Hot Electron Extraction Enabled By Single-Crystal Metal Films and Nanostructures

In contrast to conventional photovoltaic devices which rely on bulk semiconductor material absorption and separation of electron-hole pairs, surface plasmon-based solar energy harvesting employs rectifying metal/dielectric interfaces to capture light and separate charges. Here, we describe the requirements for efficient hot electron extraction in plasmonic photovoltaic devices and demonstrate a new scalable and environmentally friendly electroless deposition method for single-crystal epitaxial noble metals films and nanostructures. The method produces ultra-smooth, low loss, single-crystal noble metal films ideal for subtractive patterning of nanostructures through ion beam milling, and high definition, sub-wavelength single crystal nanostructures through lithographic patterning methods. We describe the nucleation and growth of these metal films and nanostructures in the absence and presence of anionic shape-control agents and examine the role of specific anions in determining the resulting film and nanostructure morphologies via scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). These effects have been exploited to yield large area patterned, and shape-controlled nanoarrays of single crystal metal nanostructures for plasmonic and metamaterial applications. These approaches offer new and cost effective routes to achieve crystalline, shape-controlled surface nanostructure to enable efficient hot electron extraction for energy harvesting and catalysis applications and new noble metal alloys for improved electrocatalysis.

Efficient electron extraction by CoS2 loaded onto anatase TiO2 for improved photocatalytic hydrogen evolution

Titanium dioxide (TiO2) as a benchmark photocatalyst has been attracting attention due to its photocatalytic activity combined with photochemical stability. In particular, TiO2 with anatase polymorph holds promise for driving reduction reactions, such as proton reduction to evolve H2 via photocatalysis. In this study, anatase TiO2 is loaded with CoS2 through the hydrothermal route to form a CoS2@TiO2 photocatalyst system. X-ray absorption near edge structure confirms the +2-oxidation state of the Co cation, while extended x-ray absorption fine structure shows that each Co2+ cation is primarily coordinated to six S− anions forming a CoS2-like species. A small fraction of the Co2+ species is also coordinated to O2− anions forming Co x O y species and substitutionally resides at the Ti4+-sites. Further investigations with steady-state IR absorption induced by UV-light and time-resolved microwave conductivity suggest an efficient electron transfer from the conduction band of TiO2 to the surface-loaded CoS2 which acts as a metallic material with no bandgap. The CoS2 shallowly traps electrons at the host surface and facilitates proton reduction. An appreciably enhanced H2 evolution rate (8 times) is recognised upon the CoS2 loading. The CoS2 is here proposed to function as a proton reduction cocatalyst, which can potentially be an alternative to noble metals.

Efficient and stable perovskite-silicon tandem solar cells through contact displacement by MgFx.

The performance of perovskite solar cells with inverted polarity (p-i-n) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A MgFx interlayer with thickness of ~1 nanometer at the perovskite/C60 interface favorably adjusts the surface energy of the perovskite layer through thermal evaporation, which facilitates efficient electron extraction and displaces C60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion open-circuit voltage of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a monolithic perovskite-silicon tandem solar cell ~1 square centimeter in area. The tandem retained ~95% of its initial performance after damp-heat testing (85°C at 85% relative humidity) for >1000 hours.

3D pore-matched PANI@CNT bioanode for efficient electron extraction from toluene

Microbial fuel cell (MFC) can harvest chemical energy stored in volatile organic compounds (VOCs) and consequently are of great potential for waste gas treatment and energy recovery. However, the inadequate connection between active cells and bioanode substrate hinders the extracellular electron transfer, especially in the upper layer of biofilm, resulting in restricted degradation capacity and power output. Herein, we propose a pore matching strategy to establish electron transfer nanowires around individual cells by embedding them separately inside a pore-matched sponge (core-shell polyaniline @ carbon nanotube, PANI@CNT). The resulting MFC for toluene degradation presents 4.41 times increase in power density (279.91 mW m−2), 2.64 times increase in coulombic efficiency (18.13%), and 2.02 times increase in toluene degradation activity (0.77 h−1), which also possesses considerable advantages over literature results. Furthermore, metagenomic analysis indicates that the genes for transmembrane and extracellular electron transfer are down-regulated, validating the effectiveness of the PANI@CNT nanowires linking individual cells with bioanode substrate. These findings reveal the feasibility of the pore matching strategy to boost toluene degradation and power extraction in MFC, and give an in-depth insight into transmembrane and extracellular electron transfer mechanisms.

Sputtered SnO2 as an interlayer for efficient semitransparent perovskite solar cells

SnO2 is widely used as the electron transport layer (ETL) in perovskite solar cells (PSCs) due to its excellent electron mobility, low processing temperature, and low cost. And the most common way of preparing the SnO2 ETL is spin-coating using the corresponding colloid solution. However, the spin-coated SnO2 layer is sometimes not so compact and contains pinholes, weakening the hole blocking capability. Here, a SnO2 thin film prepared through magnetron-sputtering was inserted between ITO and the spin-coated SnO2 acted as an interlayer. This strategy can combine the advantages of efficient electron extraction and hole blocking due to the high compactness of the sputtered film and the excellent electronic property of the spin-coated SnO2. Therefore, the recombination of photo-generated carriers at the interface is significantly reduced. As a result, the semitransparent perovskite solar cells (with a bandgap of 1.73 eV) based on this double-layered SnO2 demonstrate a maximum efficiency of 17.7% (stabilized at 17.04%) with negligible hysteresis. Moreover, the shelf stability of the device is also significantly improved, maintaining 95% of the initial efficiency after 800-hours of aging.

Efficient hot-carrier dynamics in near-infrared photocatalytic metals

Photoexcited metals can produce highly-energetic hot carriers whose controlled generation and extraction is a promising avenue for technological applications. While hot carrier dynamics in Au-group metals have been widely investigated, a microscopic description of the dynamics of photoexcited carriers in the mid-infrared and near-infrared Pt-group metals range is still scarce. Since these materials are widely used in catalysis and, more recently, in plasmonic catalysis, their microscopic carrier dynamics characterization is crucial. We employ \emph{ab initio} many-body perturbation theory to investigate the hot carrier generation, relaxation times, and mean free path in bulk Pd and Pt. We show that the direct optical transitions of photoexcited carriers in this metals are mainly generated in the near-infrared range. We also find that the electron-phonon mass enhancement parameter for Pt is 16 $\%$ higher than Pd, a result that help explains several experimental results showing diverse trends. Moreover, we predict that Pd (Pt) hot electrons possess total relaxation times of up to 35 fs (24 fs), taking place at approximately 0.5 eV (1.0 eV) above the Fermi energy. Finally, an efficient hot electron generation and extraction can be achieved in nanofilms of Pd (110) and Pd (100) when subject to excitation energies ranging from 0.4 to 1.6 eV.

Analysis of electron behaviour around a spring-shape filament inside a low-energy electron gun

Electron behaviour inside a low-energy electron gun based on a spring-shape filament were studied with experiment and Particle-In-Cell simulation. The energy range of the electron beam which we expected was from 1 to 20 eV. The analysis told that smaller size of filament is more useful to improve electron density in front of an extraction hole in the gun to enhance beam current. Relation between a space potential distribution in the gun and electron transport was also studied. A heater voltage to drive a filament for thermionic electron emissions has another role to form a spatial potential distribution in the gun. The potential guides electrons, which are at a distant area from the beam extraction hole, toward the hole. It can be a significant help to realize efficient electron extraction by a beam extraction electric field induced near the hole.

Recent Advances on Tin Oxide Electron Transport Layer for High-Performance Perovskite Solar Cells

In recent years, perovskite solar cells (PSCs) have been considered as a game changer for next-generation photovoltaic industry. A surge of attention originates from unprecedentedly rapid enhancement in power conversion efficiency (PCE) to reach over 25%, being competitive with commercialized silicon solar cells. The charge transporting layer, in particular, an electron transport layer (ETL) is one of the key components for high-performance PSCs. The ETL affords efficient extraction of the photo-generated electrons from the perovskite layer, which are subsequently transferred to transparent conduct oxide electrode. Tin oxide (SnO2) is one of the most attractive materials for the ETL due to its wide band gap, high optical transmission, high carrier mobility and high chemical stability. Moreover, the facile low temperature deposition process of SnO2 layer is suitable for mass production as well as versatile applications such as flexible devices. Regardless of excellent intrinsic properties, however, quality of the functional layer and resulting device performance is largely affected by the fabrication process of the material. In this study, we review the studies to utilize the SnO2 ETL for PSCs by adopting various fabrication processes, ultimately to improve efficiency and stability of the PSCs.

Self-assembled lead-free double perovskite-MXene heterostructure with efficient charge separation for photocatalytic CO2 reduction

Lead-free double perovskites with superior stability have been considered as promising non-toxic substitutes to their lead-contained counterparts in photocatalysis. However, the severe charge recombination greatly restricts their potential as high-performance photocatalysts. Herein, for the first time, we present a self-assembled heterostructure of lead-free double perovskite Cs2AgBiBr6 nanocrystals (NCs) on the surface of MXene nanosheets via mutual electrostatic attraction. The presence of MXene nanosheets effectively promotes the formation of free charge carriers in Cs2AgBiBr6 NCs via reducing the exciton binding energy. Additionally, the ultrafast photogenerated electron transfer from Cs2AgBiBr6 to MXene with a timescale of 1.1 ps largely prolongs the charge carrier lifetime by two times. As a result of the efficient charge separation and electron extraction, the Cs2AgBiBr6/MXene heterostructures achieve a high photoelectron consumption yield of 50.6 µmol g−1 h−1 for photocatalytic CO2 reduction, which surpasses most previously reported lead-free perovskite-based catalysts.

Ultrathin SnO2 Buffer Layer Aids in Interface and Band Engineering for Sb2(S,Se)3 Solar Cells with over 8% Efficiency

The environmentally friendly antimony selenosulfide (Sb2(S,Se)3) semiconductor emerges as a promising light harvester for thin-film photovoltaics owing to its excellent material and optoelectronic properties. The alloyed Sb2(S,Se)3 is endowed with the complementary benefits of Sb2S3 and Sb2Se3, such as a tunable band gap within the range of 1.10–1.70 eV. In Sb2(S,Se)3 solar cells, the n-type semiconductor CdS is extensively used as an electron transport layer (ETL), which plays a role in extracting photogenerated electrons from absorbers and transporting them to conducting substrates. However, the unsatisfactory ETL/absorber interface contact often involves severe interface recombination. Herein, we report that an ultrathin SnO2 buffer layer of ∼10 nm applied on the high-roughness fluorine-doped tin oxide (FTO) substrate aids in effective interface and band engineering for superstrate CdS/Sb2(S,Se)3 solar cells. Careful characterizations confirm that the ultrathin SnO2 buffer layer plays a positive role in inhibiting the shunt current leakage at the ETL/absorber interface and manipulating the cascade energy band structure for more effective interface passivation and efficient electron extraction. Consequently, the resultant SnO2/CdS ETL-based Sb2(S,Se)3 solar cells exhibited a remarkable device efficiency of 8.67%, coupled with a considerable open-circuit voltage of 0.72 V. Our finding demonstrates a facile approach to engineer the interface contact and band offset to accelerate electron extraction, transport, and collection efficiencies.

SnO2 Quantum Dot-Modified Mesoporous TiO2 Electron Transport Layer for Efficient and Stable Perovskite Solar Cells

As a revolutionary photovoltaic technology, the perovskite solar cell has received enormous attention, owing to excellent electronic and optical properties of perovskite materials. The mesoporous TiO2 (m-TiO2) framework is extensively used as an electron transport layer (ETL) to construct high-performance perovskite solar cells (PSCs), showing efficient electron extraction capability, owing to the enlarged perovskite/ETL interface. However, the TiO2 ETL usually involves high-density oxygen vacancies, low electron mobility, and relatively high photocatalytic activity toward perovskite materials. To address such issues, herein, we demonstrate the successful construction of SnO2 quantum dot (QD)-modified m-TiO2 as an effective ETL for PSCs. It is revealed that the SnO2 QD-modified m-TiO2 ETL affords more favorable electron extraction and transport characteristics and suppressed charge recombination, resulting from the interfacial passivation and the enhanced conductivity of ETLs. Furthermore, the ultrathin SnO2 QD layer incorporated at the m-TiO2/perovskite interface effectively lowers the photocatalytic activity of TiO2 toward perovskite materials, thereby improving the long-term device stability. Eventually, the MAPbI3- and FAPbI3-based PSCs utilizing the SnO2 QD-modified m-TiO2 ETLs obtained appreciable power conversion efficiencies of 19.09 and 20.09%, respectively, higher than those of counterpart devices based on the conventional m-TiO2 and SnO2 ETLs.