Efficient Electron Transport Layer Research Articles

Pr3+ ions activated TiO2 nanoparticles as electron transport layer for copper based (CH3NH2)2CuBr4 perovskites solar cells

In emerging organic-inorganic perovskite solar cells (PSCs), the role of efficient electron transport layers (ETLs) is critical for electron transfer and hole blocking. TiO2 is one of the widely reported ETLs but limits the performance of the devices exhibiting restricted electron mobility and numerous defect states. The process of doping rare earth ions has been an effective approach in improving the electronic and optical properties of TiO2 for enhanced efficiency of PSCs. The present work studies the effect of praseodymium (Pr3+) doped TiO2 prepared via sol-gel technique as electron transport layers for lead-free perovskite solar cells. The X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS) studies showed that the crystallite size and bandgap of the particles reduced as a function of Pr3+ doping concentration. The X-ray photoelectron spectroscopy (XPS) analysis of the samples inferred that Pr3+ ions majorly remained on the TiO2 surface. Copper-based (CH3NH2)2CuBr4 perovskites were synthesized by solution method as an active layer for the solar cells. XRD, FTIR (Fourier Transform Infrared Spectroscopy) and XPS analysis confirmed the formation of 2D-perovskite phase of the samples. The scanning electron microscopy (SEM) analysis of the perovskites revealed well crystalline orthorhombic structures. Current-voltage measurements were carried out to study better passivation properties with rare-earth doping of the ETLs and was found to be most enhanced for 0.07 Pr3+ concentration. Electro-chemical Impedance Spectroscopy (EIS) studies of the solar cells showed a reduced interface recombination and enhance charge transfer properties as a function of rare-earth dopant concentration. Further, the fabricated perovskite solar cells showcased better performance with xPr3+:TiO2 ETLs and the maximum efficiency of ∼1.25 % was obtained for TiO2: 0.07 Pr3+.

Mesoporous structured MoS2 as an electron transport layer for efficient and stable perovskite solar cells.

Mesoporous structured electron transport layers (ETLs) in perovskite solar cells (PSCs) have an increased surface contact with the perovskite layer, enabling effective charge separation and extraction, and high-efficiency devices. However, the most widely used ETL material in PSCs, TiO2, requires a sintering temperature of more than 500 °C and undergoes photocatalytic reaction under incident illumination that limits operational stability. Recent efforts have focused on finding alternative ETL materials, such as SnO2. Here we propose mesoporous MoS2 as an efficient and stable ETL material. The MoS2 interlayer increases the surface contact area with the adjacent perovskite layer, improving charge transfer dynamics between the two layers. In addition, the matching between the MoS2 and the perovskite lattices facilitates preferential growth of perovskite crystals with low residual strain, compared with TiO2. Using mesoporous structured MoS2 as ETL, we obtain PSCs with 25.7% (0.08 cm2, certified 25.4%) and 22.4% (1.00 cm2) efficiencies. Under continuous illumination, our cell remains stable for more than 2,000 h, demonstrating improved photostability with respect to TiO2.

Atom layer deposited TiO2 electron transport layer for silicon heterojunction solar cells to achieve high performance

Silicon/compound heterojunction (SCH) solar cells based on p-type and n-type c-Si wafers using atom layer deposition-TiO2 and low work function metal as the electron transport layer and rear electrode are fabricated. Efficiencies of 20.6 % and 21.6 % are achieved on p-type and n-type silicon solar cells, respectively. High Voc exceeding 700 mV have been realized on both kinds of Si wafers. Special attention has been paid to the SCH solar cells based on p-type c-Si wafers in which the TiO2 electron transport layer serves as the emitter. Carrier transport mechanisms and junction characteristics of the SCH solar cells are analyzed based on dark J-V measurement. The formation of a strong inversion layer at the Si surface region is determined, which implies the high Voc potential of the SCH solar cells based on p-type Si. An optical loss analysis is performed along with a possible solution to further improve the Jsc. The feasibility of TiO2 applied as an efficient electron transport layer (emitter) in p-type SCH solar cells with high performance has been showed.

Synthesis and simulation study of titanium dioxide-based nanomaterial for electron carrier selective contact solar cell

This research introduces a novel approach to synthesizing titanium dioxide (TiO2) nanomaterials using the sol–gel method, specifically aimed at enhancing the performance of Silicon Heterojunction (SHJ) solar cells. The innovation lies in utilizing Iso-Propanol Alcohol and Titanium Tetra Isopropoxides for synthesis, leveraging TiO2’s wide bandgap and low work function to replace the conventional n-doped amorphous silicon layer. This approach is expected to overcome the limitations of traditional materials and significantly improve electron transport efficiency. Advanced characterization techniques were employed to assess the synthesized TiO2 nanomaterials. Atomic Force Microscopy (AFM) measured the roughness and 3D profile, while UV-V spectrophotometry evaluated the absorption properties. The structure and surface morphology were meticulously analyzed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). These comprehensive analyses ensured a detailed understanding of the nanomaterials’ physical properties. Simulations conducted with the AFORS-HET simulator revealed that TiO2, with a refractive index compatible with a-Si:H(n) and a work function of 4.6 eV, significantly enhances SHJ solar cell performance. The results demonstrated a remarkable 22.57 % improvement in efficiency, achieving an open-circuit voltage (Voc) of 716.8 mV, a short-circuit current density (Jsc) of 37.71 mA/cm2 and a fill factor (FF) of 83.49 %. These findings underscore the potential of TiO2 nanomaterials to revolutionize SHJ solar cell technology by providing a more efficient and effective electron transport layer. Future research will focus on refining the nanostructure of TiO2 further to enhance its photovoltaic applications, aiming to push the boundaries of current solar cell efficiencies even further. This study marks a significant advancement in the field of photovoltaic materials, presenting a novel and promising solution to improving solar energy conversion.

Naphthalene Diimide-Modified SnO2 Enabling Low-Temperature Processing for Efficient ITO-Free Flexible Perovskite Solar Cells.

A low-cost and indium-tin-oxide (ITO)-free electrode-based flexible perovskite solar cell (PSC) that can be fabricated by roll-to-roll processing shall be developed for successful commercialization. High processing temperatures present a challenge for the PSC fabrication on flexible substrates. The most efficient planar n-i-p PSC structures, which utilize a metal oxide as an electron transport layer (ETL), necessitate high annealing temperatures. In addition, the device performance deteriorates owing to the migration of halogen ions, which causes the oxidation of the metal electrodes. These drawbacks conflict with the development of highly efficient flexible PSCs fabricated on ITO-free transparent electrodes. Herein, an efficient ETL material that enables low-temperature processing is presented. Tin dioxide (SnO2) is modified by (sulfobetaine-N,N-dimethylamino)propyl naphthalene diimide (NDI-B) and used as an ETL. The NDI-B effectively reduces the interfacial nonradiative recombination between the ETL and perovskite and suppresses the ion migration by passivating oxygen-vacancy defects in SnO2 and strongly interacting with halogen ions, respectively. Based on the NDI-B-blended SnO2 ETL, a record PCE of 17.48% is achieved in the ITO-free flexible PSC fabricated at low temperature.

Analysis of lead free CsSnBr3 based perovskite solar cells utilizing numerical modeling

In this study, we propose several CsSnBr3-based PSC configurations using the Solar Cell Capacitance Simulator (SCAPS-1D), incorporating various efficient Electron transport layers (ETLs) such as TiO2, PCBM, WS2, SnO2, ZnO, IGZO, C60, and Hole transport layers (HTLs) like CBTS, CFTS, CuO, CuI, Spiro-OMeTAD, PEDOT:PSS, P3HT, CuSbS2, CuSCN, and Cu2O. Numerical simulation results reveal that the device structure ITO/WS2/CsSnBr3/Cu2O/Au exhibits outstanding power conversion efficiency (PCE), retaining the closest photovoltaic parameter values among 70 different configurations. In this configuration, WS2 served as the ETL, and Cu2O acted as the HTL. This device achieved an outstanding peak PCE of 20.02%. It also boasted a high open circuit voltage (Voc) of 1.23 V, a short circuit current density (Jsc) of 19.32 mA cm−2, and an impressive fill factor (FF) of 84.18%. In comparison, devices utilizing materials like TiO2, PCBM, SnO2, ZnO, IGZO, and C60 yielded PCE values of 19.72, 19.73, 19.72, 19.73, 19.72, and 15.60%, respectively. Furthermore, for the seven best-performing configurations, we investigated the effects of CsSnBr3 absorber thickness, absorber-acceptor doping density (NA), conduction band offset (CBO), ETL doping density (ND), Capacitance–Voltage (C-V), Mott–Schottky (M-S) characteristics, generation and recombination rates, series resistance (Rse), shunt resistance (Rsh), temperature, current–voltage characteristics (J-V), and quantum efficiency (QE) on performance metrics. Our findings indicate that all seven ETLs, when combined with Cu2O HTL, can serve as excellent materials for fabricating high-efficiency CsSnBr3-based PSCs with the ITO/ETL/CsSnBr3/Cu2O/Au structure. To validate our results, we compared the simulation outcomes obtained with SCAPS-1D for the best seven CsSnBr3-PSC configurations with previously published research works. This comprehensive simulation study opens a promising avenue for the cost-effective production of high-performance, lead-free CsSnBr3-based PSCs, contributing to a greener and pollution-free environment.

Perylene Diimide‐Based Low‐Cost and Thickness‐Tolerant Electron Transport Layer Enables Polymer Solar Cells Approaching 19% Efficiency

AbstractThe materials for electron transport layers (ETLs) play a significant role in the performance of polymer solar cells (PSCs) but face challenges, such as low electron transport mobility and conductivity, low solution processibility, and extreme thickness sensitivity, which will undermine the photovoltaic performance and hinder compatibility of large‐scale fabrication technique. To address these challenges, a new n‐type perylene diimide‐based molecule (PDINB) with two special amine‐anchored long‐side chains is designed and synthesized feasibly. PDINB shows very high solubility in common organic solvents, such as dichloromethane (>75 mg ml−1) and methanol with acetic acid as an additive (>37 mg ml−1), which leads to excellent film formability when deposited on active layers. With PDINB as ETLs, the photovoltaic performance of the PSCs is boosted comprehensively, leading to power conversion efficiency (PCE) up to 18.81%. Thanks to the strong self‐doping effect and high conductivity of PDINB, it displays an appreciable thickness‐tolerant property as ETLs, where the devices remain consistently high PCE values with the thickness varying from 5 to 30 nm. Interestingly, PDINB can be used as a generic ETL in different types of PSCs including non‐fullerene PSCs and all‐polymer PSCs. Therefore, PDINB can be a potentially competitive candidate as an efficient ETL for PSCs.

Band alignment studies of Zn1-xNixO/ZnO: As bilayer electron transport layer in perovskite solar cells

An efficient electron transport layer (ETL) is an essential requirement for performance and stability for perovskite solar cells. In this study, we have opted Zn1-xNixO/ZnO bilayer as is used electron transport layer instead of the ZnO single layer to overcome the trap-assisted recombination and also to enhance energy level alignment in the solar cell. For this, pristine ZnO and Ni-doped ZnO (Ni–ZnO) thin films were deposited on fused silica (Quartz) by pulsed laser deposition (PLD). For confirmation of the structural properties of deposited thin films, X-ray diffraction has been used. Electron affinity and band gap of these films have been evaluated by UPS and UV–Vis spectroscopy to design Zn1-xNixO/ZnO bilayer ETL. Further, planar perovskite solar cell has been schematized and simulated using SCAPS-1D software using experimentally designed bilayer ETL.

Fine tuning of Nb-incorporated TiO2 thin films by atomic layer deposition and application as efficient electron transport layer in perovskite solar cells

Access to finely tuned thin films that can act as electron transport layer (ETL) and adapt to the absorber composition and whole cell fabrication process is key to achieve efficient perovskite-based solar cells. In this study, the growth of mixed niobium-titanium oxide (Nb-TiO2) thin films by atomic layer deposition and its use to extract photogenerated electrons is reported. Films were obtained at 200 °C from titanium (IV) i-propoxide, (t-butylimido)tris(diethylamido)niobium(V), and water by introducing Nb2O5 growth cycle in a TiO2 matrix. Process parameters (order of precursor introduction, cycle ratio) were optimized; the growth mechanism and the effective Nb incorporation were investigated by an in situ quartz crystal microbalance and x-ray photoelectron spectroscopy. The composition, morphology, structural, and optoelectronic properties of the as-deposited films were determined using a variety of characterization techniques. As a result, a fine control of the film properties (between TiO2 and Nb2O5 ones) could be achieved by tuning Nb content. To allow a successful implementation in solar devices, a comprehensive annealing study under several conditions (temperatures, various atmospheres) was conducted leading to an evolution of the optical properties due to a morphological change. Ultimately, the incorporation of these 15 nm-thick films in mesoscopic perovskite solar cells as ETL shows an improvement of the cell performances and of their stability with increasing Nb content, in comparison of both TiO2 and Nb2O5 pure compounds, reaching power conversion efficiency up to 18.3% and a stability above 80% of its nominal value after 138 h under illumination.

Recycled or Bio-Based Solvents for the Synthesis of ZnO Nanoparticles: Characterization and Validation in Organic Solar Cells.

Among solution-processable metal oxides, zinc oxide (ZnO) nanoparticle inks are widely used in inverted organic solar cells for the preparation, at relatively low temperatures (<120 °C), of highly efficient electron-transporting layers. There is, however, a recent interest to develop more sustainable and less impacting methods/strategies for the preparation of ZnO NPs with controlled properties and improved performance. To this end, we report here the synthesis and characterization of ZnO NPs obtained using alternative reaction solvents derived from renewable or recycled sources. In detail, we use (i) recycled methanol (r-MeOH) to close the loop and minimize wastes or (ii) bioethanol (b-EtOH) to prove the effectiveness of a bio-based solvent. The effect of r-MeOH and b-EtOH on the optical, morphological, and electronic properties of the resulting ZnO NPs, both in solution and thin-films, is investigated, discussed, and compared to an analogous reference material. Moreover, to validate the properties of the resulting materials, we have prepared PTB7:PC71BM-based solar cells containing the different ZnO NPs as a cathode interlayer. Power conversion efficiencies comparable to the reference system (≈7%) were obtained, validating the proposed alternative and more sustainable approach.

Single‐Layer Carbon Nitride as an Efficient Metal‐Free Organic Electron‐Transport Material with a Tunable Work Function

AbstractSingle‐layer carbon nitride (SLCN) is introduced as a metal‐free organic electron transport material (ETL) for organic solar cells, delivering a performance comparable to that of the benchmark nanocrystalline ZnO. SLCN is produced in the form of stable aqueous inks and can serve as an efficient electron transport layer for three different types of active layers, showing high stability to photodegradation. A lower conductivity of SLCN films as compared to ZnO is counter‐balanced by their higher transparency and lower light scattering losses. The SLCN ETL provides a unique opportunity to tune the work function from ca. −4.1 to −4.6 eV by varying the annealing temperature due to partial thermal oxidation of the SLCN film. The PL band position follows the oxidation‐induced changes of the work function allowing PL properties of SLCN to be used to predict the PV efficiency. The 2D structure of SLCN coupled with unique structural and compositional variability, and tunability of the work function show a high promise for emerging organic PV devices.

Doping of ZnO Electron Transport Layer with Organic Dye Molecules to Enhance Efficiency and Photo-Stability of the Non-Fullerene Organic Solar Cells.

The solution-processed zinc oxide (ZnO) electron transport layer (ETL) always exhibits ubiquitous defects, and its photocatalytic activity is detrimental for the organic solar cell (OSC) to achieve high efficiency and stability. Herein, an organic dye molecule, PDINN-S is introduced, to dope ZnO, constructing a hybrid ZnO:PDINN-S ETL. This hybrid ETL exhibits improved electron mobility and conductivity, particularly post-light exposure. The catalytic activity of ZnO is also effectively suppressed.Consequently, the efficiency and photo-stability of inverted non-fullerene OSCs are synergistically enhanced. The devices based on PM6:Y6/PM6:BTP-eC9 active layer with ZnO:PDINN-S as ETL give impressive power conversion efficiencies (PCEs) of 16.78%/17.59%, significantly higher than those with pure ZnO as ETL (PCEs=15.31%/16.04%). Moreover, ZnO:PDINN-S-based device shows exceptional long-term stability under continuous AM 1.5Gillumination (T80 = 1130 h) , overwhelming the reference device (T80 = 455h). In addition, IncorporatingPDINN-S into ZnO alleviate mechanical stress within the inorganic lattice, making ZnO:PDINN-S ETL more suitable for the fabrication of flexible devices. Overall, doping ZnO with organic dye molecules offers an innovative strategy for developing multifunctional and efficient hybrid ETL of the non-fullerene OSCs with excellent efficiency and photo-stability.

Highly Crystalized Cl-Doped SnO2 Nanocrystals for Stable Aqueous Dispersion Toward High-Performance Perovskite Photovoltaics.

Tin dioxide (SnO2 ) with high conductivity and low photocatalytic activity has been reported as one of the best candidates for highly efficient electron transport layer (ETL) in perovskite solar cell (PSC). The state-of-the-art SnO2 layer is achieved by chemical bath deposition with tunable properties, while the commercial SnO2 nanocrystals (NCs) with low tunability still face the necessity of further improvement. Here, a kind of highly crystallized Cl-doped SnO2 NCs is reported that can form very stable aqueous dispersion with shelf life up to one year without any stabilizer, which can facilitate the fabrication of PSCs with satisfactory performance. Compared to the commercial SnO2 NCs regardless of the extrinsic Cl-doping conditions, the intrinsic Cl-doped SnO2 NCs effectively suppress the energy barrier and reduces the trap state density at the buried interface between perovskite and ETL. Consequently, stable PSCs based on such Cl-doped SnO2 NCs achieve a champion efficiency up to ≈25% for small cell (0.085 cm2 ) and ≈20% for mini-module (12.125 cm2 ), indicating its potential as a promising candidate for ETL in high-performance perovskite photovoltaics.

TiCl4 precursor affecting the performance of HTM-free carbon-based perovskite solar cell

The presence of TiO2 used as an efficient electron transport layer is crucial to achieving high-performance solar cells, especially for a hole transport material (HTM)-free carbon-based perovskite solar cell (PSC). The hydrolysis of TiCl4 is one of the most widely used routes for forming TiO2 layer in solar cells, which includes the stock solution preparation from TiCl4 initial precursor and the thermal hydrolysis of the stock solution. The second thermal hydrolysis step has been extensively studied, while the initial hydrolysis reaction in the first step is not receiving sufficient attention, especially for its influence on the photovoltaic performance of HTM-free carbon-based devices. In this study, the role of TiCl4 stock solution in the growth process of TiO2 layer is examined. Based on the analysis of the Ti(IV) intermediate states for different TiCl4 concentrations from Raman spectra, 2 M TiCl4 precursor exhibits moderate nucleation and growth kinetics without generating too many intermediates which occurs in 3 M TiCl4 precursor, yielding ∼300 nm size spherical TiO2 agglomerates with a rutile phase. In the aspect of devices, the HTM-free carbon-based PSCs fabricated using 2 M TiCl4 precursor deliver a conversion efficiency beyond 17%, which may be attributed to the reduced defect in compact TiO2 layer.

Ferrocene‐Terminated Perylene Diimide‐Based Small Molecular Electrolyte as Electron‐Transport Layer for Efficient Organic Solar Cells

The electron‐transport layer (ETL) is essential for achieving high performance and stability of organic solar cells (OSCs). However, most organic ETLs suffer from low conductivity, low electron mobility, and difficult modification, resulting in mitigation of charge collection and transport. Metal–organic complex, such as ferrocene, is a promising candidate to improve organic ETL due to their excellent film‐forming property, easy preparation, and high electrical properties. Herein, a small molecule, PDIN‐Fc, based on PDIN modified by ferrocene is designed, which can be synthesized by environmentally friendly esterification and quaternization reactions. PDIN‐Fc displays outstanding alcohol solubility and tunable work function. Interestingly, introducing the ferrocene group can lead to increased self‐doping of PDIN‐Fc. As a result, PDIN‐Fc shows significantly improved charge transport performance and conductivity compared to PDIN. When using PM6:L8‐BO as the photoactive layer, the OSCs with PDIN‐Fc as ETL achieve a remarkable power conversion efficiency of 18.45% and exhibit notable high light stability. This study demonstrates an effective strategy to design efficient ETLs by incorporating metal complexes, which enable thickness insensitivity, good stability, and high‐performance photovoltaic devices.

Edge-modified phosphorene nanoribbons enhance interfacial carrier extraction in perovskite solar cells

The search for cheap, stable and efficient electron and hole transport layers (ETL and HTL) of perovskite solar cells (PVSCs) remains a significant challenge. In this study, we construct a series of edge-modified phosphorene nanoribbons (PNRs) and explore their potentials as either ETL or HTL in PVSCs using PNRs/MAPbI3 heterojunction. The results reveal that the different functional groups have distinct effects on the electronic structures of individual PNRs. When combined with MAPbI3, the electronic structures of PNRs are further regulated due to the strong interaction. Considering the combined influence of both modifying groups and MAPbI3, several PNRs/MAPbI3 including COH-PNR/MAPbI3, OCN-PNR/MAPbI3 and CN-PNR/MAPbI3 show the tendency for electron transfer from MAPbI3 to PNRs. Conversely, NH2-PNR/MAPbI3 has a possibility for hole transfer. The time-domain noncollinear DFT-based nonadiabatic carrier dynamics simulations for H-PNR/MAPbI3, CN-PNR/MAPbI3 and NH2-PNR/MAPbI3 validate that the –CN group facilitates interfacial electron transfer, while the –NH2 group promotes hole transfer compared to H-PNR/MAPbI3. The addition of modifying groups increases the number of states of the PNRs in PNRs/MAPbI3 that are capable of accepting electron or hole from MAPbI3, thereby enhancing the carrier extraction capacity. This computational work proposes a design strategy to enhance the efficiency of ETL and HTL in PVSCs.

Efficient and stable inverted structure organic solar cells utilizing surface-modified SnO2 as the electron transport layer

Organic solar cells (OSCs) with an inverted structure have the potential to exhibit both high efficiency and stability, in which the electron transport layer (ETL) plays a crucial role. In this study, we have developed an efficient ETL for inverted structure OSCs by modifying commercially available SnO2 nanoparticles with a simple molecule 2-(3-(dimethylamino)propyl)− 1,3-dioxo-2,3-dihydro-1 H-benzo[de]isoquinoline-6,7-dicarboxylic acid (NMA). The surface modification effectively eliminates the light soaking issue observed in devices with bare SnO2. Furthermore, it significantly enhances the efficiency and stability of the photovoltaic devices. With the hybrid ETL, the device based on PM6:L8-BO achieves an outstanding power conversion efficiency (PCE) of 18.33 %. Notably, the champion device exhibits excellent shelf, thermal and photo stabilities. It maintained 99.7 % and 87.1 % of its original efficiency under storage in N2 and thermal stress at 65 ℃ for 1000 h, respectively. Under continuous 1-sun illumination with maximum power point tracking for 800 h, the device retained 86.6 % of its initial efficiency. Additionally, the hybrid ETL shows good generality on other typical active layer systems based-OSCs. This work presents an effective hybrid ETL approach for the development of high-performance OSCs.

Review on Surface Modification of SnO2 Electron Transport Layer for High-Efficiency Perovskite Solar Cells

In the planar heterojunction perovskite solar cell (PSC) structure, among numerous contenders, tin oxide (SnO2) has been utilized, instead of TiO2, as the material for the electron transport layer (ETL) owing to its good band alignment, ultraviolet light resistance, strong charge extraction, and low photocatalytic activity. However, the morphology of the SnO2 ETL has proven to be unstable under low-temperature processing, leading to low electron extraction in PSCs. Therefore, the surface morphology must be modified to achieve high-performance PSCs. In this review, we provide an overview of the fundamental insights into how surface variations affect the ETL performance. The significance and the design rule of surface modification for an efficient SnO2 ETL, that is, the intentional alteration of the SnO2 interface, are discussed. Based on the evaluations, distinct surface engineering procedures and how they are implemented are presented. The effects of chemical and physical interactions on the properties of SnO2 are elucidated in detail; these have not been considered in previous studies. Finally, we provide an outlook on, highlight the key challenges in, and recommend future research directions for the design of the interfaces of highly efficient and stable PSCs.

Pyridine group incorporated mixed electron transporting layers for high-performance perovskite light-emitting diodes

The unsaturated Pb2+ ions, located at the perovskite/charge transport layer (CTL) interfaces, are one of the main trap centers that result in non-radiative recombination of perovskite light-emitting diodes (PeLEDs), thus compromising device efficiency. Therefore, interface engineering and modulation are of significance in passivating the surface defects of the perovskite film as well as modifying the perovskite/CTL interface properties. In this work, a high-mobility pyridine-based electron transport material, 1,3,5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB), is co-evaporated with 2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) to form efficient electron-transport layers (ETLs) for PeLEDs. The interaction of the pyridine group of TmPyPB with the uncoordinated Pb2+ ions can effectively passivate the perovskite defects. Furthermore, the mixed ETL can also enhance electron mobility by tuning the mixing ratios between the TmPyPB and TPBi, thus boosting the device efficiency. As a result, PeLEDs with enhanced electron mobility and reduced defects are prepared, in which the device exhibits a maximum current density (CE) of 74 cd/A and an external quantum efficiency (EQE) of 25.4%. This EQE is nearly two fold higher than that of the pure TPBi-based PeLEDs.

Preparation of TiO2/SnO2 Electron Transport Layer for Performance Enhancement of All-Inorganic Perovskite Solar Cells Using Electron Beam Evaporation at Low Temperature.

SnO2 has attracted much attention due to its low-temperature synthesis (ca. 140 °C), high electron mobility, and low-cost manufacturing. However, lattice mismatch and oxygen vacancies at the SnO2/CsPbI3-xBrx interface generally lead to undesirable nonradiative recombination in optoelectronic devices. The traditional TiO2 used as the electron transport layer (ETL) for all-inorganic perovskite solar cells (PSCs) requires high-temperature sintering and crystallization, which are not suitable for the promising flexible PSCs and tandem solar cells, raising concerns about surface defects and device uniformity. To address these challenges, we present a bilayer ETL consisting of a SnO2 layer using electron beam evaporation and a TiO2 layer through the hydrothermal method, resulting in an enhanced performance of the perovskite solar cell. The bilayer device exhibits an improved power conversion efficiency of 11.48% compared to the single-layer device (8.09%). The average fill factor of the bilayer electron transport layer is approximately 15% higher compared to the single-layer electron transport layer. Through a systematic investigation of the use of ETL for CsPb3-xBrx PSCs on optical and electronic properties, we demonstrate that the SnO2/TiO2 is an efficient bilayer ETL for PSCs as it significantly enhances the charge extraction capability, suppresses carrier recombination at the ETL/perovskite interface, facilitates efficient photogenerated carrier separation and transport, and provides high current density and reduced hysteresis.