Highly efficient flexible perovskite solar cells with vacuum-assisted low-temperature annealed SnO2 electron transport layer

The demand for lightweight, flexible, and high-performance portable power sources urgently requires high-efficiency and stable flexible solar cells. In the case of perovskite solar cells(PSCs), most of the common electron transport layer(ETL) needs to be annealed for improving the optoelectronic properties,while conventional flexible substrates could barely stand the high temperature. Herein, a vacuumassisted annealing SnO_(2) ETL at low temperature(100℃) is utilized in flexible PSCs and achieved high efficiency of 20.14%. Meanwhile, the open-circuit voltage(V_(oc)) increases from 1.07 V to 1.14 V. The flexible PSCs also show robust bending stability with 86.8% of the initial efficiency is retained after 1000 bending cycles at a bending radius of 5 mm. X-ray photoelectron spectroscopy(XPS), atomic force microscopy(AFM), and contact angle measurements show that the density of oxygen vacancies, the surface roughness of the SnO_(2) layer, and film hydrophobicity are significantly increased, respectively. These improvements could be due to the oxygen-deficient environment in a vacuum chamber, and the rapid evaporation of solvents. The proposed vacuum-assisted low-temperature annealing method not only improves the efficiency of flexible PSCs but is also compatible and promising in the large-scale commercialization of flexible PSCs.

Composite electron transport layer for efficient N-I-P type monolithic perovskite/silicon tandem solar cells with high open-circuit voltage

Perovskite/silicon tandem solar cells(PSTSCs) have exhibited huge technological potential for breaking the Shockley-Queisser limit of single-junction solar cells. The efficiency of P-I-N type PSTSCs has surpassed the single-junction limit, while the performance of N-I-P type PSTSCs is far below the theoretical value. Here, we developed a composite electron transport layer for N-I-P type monolithic PSTSCs with enhanced open-circuit voltage(VOC) and power conversion efficiency(PCE). Lithium chloride(Li Cl) was added into the tin oxide(SnO_(2)) precursor solution, which simultaneously passivated the defects and increased the electron injection driving force at the electron transfer layer(ETL)/perovskite interface.Eventually, we achieved monolithic PSTSCs with an efficiency of 25.42% and V_(OC) of 1.92 V, which is the highest PCE and VOCin N-I-P type perovskite/Si tandem devices. This work on interface engineering for improving the PCE of monolithic PSTSCs may bring a new hot point about perovskite-based tandem devices.

Inverted organic solar cells with solvothermal synthesized vanadium-doped TiO2 thin films as efficient electron transport layer

We investigated the effects of using different thicknesses of pure and vanadium-doped thin films of TiO2 as the electron transport layer in the inverted configuration of organic photovoltaic cells based on poly（3-hexylthiophene） P3HT：[6-6] phenyl-（6） butyric acid methyl ester（PCBM）. 1% vanadium-doped TiO2nanoparticles were synthesized via the solvothermal method. Crystalline structure, morphology, and optical properties of pure and vanadium-doped TiO2 thin films were studied by different techniques such as x-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and UV–visible transmission spectrum. The doctor blade method which is compatible with roll-2-roll printing was used for deposition of pure and vanadium-doped TiO2 thin films with thicknesses of 30 nm and 60 nm. The final results revealed that the best thickness of TiO2 thin films for our fabricated cells was 30 nm. The cell with vanadium-doped TiO2 thin film showed slightly higher power conversion efficiency and great Jsc of 10.7 mA/cm^2 compared with its pure counterpart. In the cells using 60 nm pure and vanadium-doped TiO2 layers, the cell using the doped layer showed much higher efficiency. It is remarkable that the external quantum efficiency of vanadium-doped TiO2 thin film was better in all wavelengths.

TiO_2 composite electron transport layers for planar perovskite solar cells by mixed spray pyrolysis with precursor solution incorporating TiO_2 nanoparticles

Perovskite solar cells with planar structure are attractive for their simplified device structure and reduced hysteresis effect. Compared to conventional mesoporous devices, TiO2 porous scaffold layers are removed in planar devices. Then, compact TiO2 electron transport layers take the functions of extracting electrons, transporting electrons, and blocking holes. Therefore, the properties of these compact TiO2 layers are important for the performance of solar cells. In this work, we develop a mixed spray pyrolysis method for producing compact TiO2 layers by incorporating TiO2 nanoparticles with dif- ferent size into the precursor solutions. For the optimized nanoparticle size of 60 nm, a power conversion efficiency of 16.7% is achieved, which is obviously higher than that of devices without incorporated nanoparticles （9.9%）. Further in- vestigation reveals that the incorporation of nanoparticles can remarkably improve the charge extraction and recombination processes.

TiO_2 nanoparticle-based electron transport layer with improved wettability for efficient planar-heterojunction perovskite solar cell

The electron transport layer （ETL） plays an important role in planar heterojunction perovskite solar cell （PSCs）, by affecting the light-harvesting, electron injection and transportation processes, and especially the crystal- lization of perovskite absorber. In this work, we utilized a commercial TKD-TiO2 nanoparticle with a small diameter of 6 nm for the first time to prepare a compact ETL by spin coating. The packing of small-size particles endowed TKD-TiO2 ETL an appropriate surface-wettability, which is beneficial to the crystallization of perovskite deposited via solution-processed method. The uniform and high-transmittance TKD-TiO2 films were successfully incorporated into PSCs as ETLs. Further careful optimization of ETL thickness gave birth to a highest power conversion efficiency of 11.0%, which was much higher than that of PSC using an ETL with the same thickness made by spray pyrolysis. This TKD-TiO2 provided a universal solar material suitable for the further large-scale production of PSCs. The excellent morphology and the convenient preparation method of TKD-TiO2 film gave it an extensive application in photovoltaic devices.

Efficient fully laser-patterned flexible perovskite modules and solar cells based on low-temperature solution-processed SnO2/mesoporous-TiO2 electron transport layers

Efficient flexible perovskite solar cells and modules were developed using a combination of SnO2 and mesoporous-TiO2 as a fully solution-processed electron transport layer （ETL）. Cells using such ETLs delivered a maximum power conversion efficiency （PCE） of 14.8%, which was 30% higher than the PCE of cells with only SnO2 as the ETL. The presence of a mesoporous TiO2 scaffold layer over SnO2 led to higher rectification ratios, lower series resistances, and higher shunt resistances. The cells were also evaluated under 200 and 400 lx artificial indoor illumination and found to deliver maximum power densities of 9.77 μW/cm^2 （estimated PCE of 12.8%） and 19.2 μW/cm^2 （estimated PCE of 13.3%）, respectively, representing the highest values among flexible photovoltaic technologies reported so far. Furthermore, for the first time, a fully laser-patterned flexible perovskite module was fabricated using a complete three-step laser scribing procedure （P1, P2, P3） with a PCE of 8.8% over an active area of 12 cm^2 under an illumination of 1 sun.

Inducing the SnO2-based electron transport layer into NiFe LDH/NF as efficient catalyst for OER and methanol oxidation reaction

In an electrocatalyst with a heterointerface structure,the different interfaces can efficiently adjust the catalyst’s conductivity and electron arrangement,thereby enhancing the activity of the electrocatalyst.Ultrathin and smaller Ni Fe LDH was successfully constructed on the surface of SnOnanosheet supported NF by layer by layer assembly,and exhibits lower overpotential of 234 mV at a current density of 10 m A cm,which only increases by 6.4%even at a high current density of 100 mA cm.The excellent OER activity of catalyst is attributed to the contribution of the semiconductor SnOelectron transport layer.Through experiments and characterization,3d structure SnOnanosheets control the growth of ultra-thin nickel-iron,the hierarchical interface between SnOand Ni Fe LDH can change the electron arrangement around the iron and nickel active centers at the interface,resulting the valence states of iron slightly increased and Nicontent increased.The result will promote the oxidation of water.Meanwhile,the SnOsemiconductor as electron transport layer is conducive to trapping electrons generated in oxidation reaction,promoting electrons transferring from the Ni Fe LDH active center to the Ni substrate more quickly,and enhance the activity of Ni Fe LDH.It also shows excellent activity in an electrolyte solution containing 0.5 M methanol and 1 M KOH,and only 1.396 V(vs.RHE)is required to drive a current density of 10 mA cm.

Low-temperature-processed metal oxide electron transport layers for efficient planar perovskite solar cells

As a promising photovoltaic technology, perovskite solar cells(pero-SCs) have developed rapidly over the past few years and the highest power conversion efficiency is beyond 25%. Nowadays, the planar structure is universally popular in pero-SCs due to the simple processing technology and low-temperature preparation.Electron transport layer(ETL) is verified to play a vital role in the device performance of planar pero-SCs. Particularly, the metal oxide(MO) ETL with low-cost, superb versatility, and excellent optoelectronic properties has been widely studied. This review mainly focuses on recent developments in the use of low-temperature-processed MO ETLs for planar pero-SCs. The optical and electronic properties of widely used MO materials of TiO_(2), ZnO, and SnO_(2), as well as the optimizations of these MO ETLs are briefly introduced. The commonly used methods for depositing MO ETLs are also discussed. Then, the applications of different MO ETLs on pero-SCs are reviewed.Finally, the challenge and future research of MO-based ETLs toward practical application of efficient planar peroSCs are proposed.

Research progress in electron transport layer in perovskite solar cells

Since perovskite solar cells appeared in 2009, its simple preparation process, high photoelectric conversion efficiency and the characteristic of low cost in preparation process let it become the hot spot of both at-home and abroad. Owing to the constant efforts of scientists, the conversion efficiency of perovskite solar cells is more than 20% now. Perovskite solar cells are mainly composed of conductive glass, electron transport layer and hole transport layer, perovskite layer and electrode parts. This paper will briefly introduce the working principle and working pro- cess about the electron transport layer of perovskite solar cells. The paper focuses on aspects such as material types （e.g., inorganic electron transport materials, organic small molecule electron transport materials, surface modified electron transport materials and doped electron transport materials）, preparation technology of electron transport layer, the effects of electron transport layer on the photo- voltaic performance of the devices, and the electron transport layer in the future research.

Bending-stability Interfacial Layer as Dual Electron Transport Layer for Flexible Organic Photovoltaics

The flexibility of organic photovoltaics(OPVs)has attracted worldwide attention in recent years.To realize the bending-stability of OPVs,it is necessary to put forward the bending-stability of interfacial layer.A novel bendable composite is explored and successfully applied as an electron transport layer(ETL)for fully-flexible OPVs.We incorporated poly(vinylpyrrolidone)(PVP)into conjugated electrolytes(CPE)to composite a bendable ETL for high-performance OPVs devices.Fortunately,the devices based on PVP-modified CPE exhibited better device performances and more excellent mechanical properties of bendability.The fullerene-free OPVs based on PM6:IT-4 F with CPE@PVP as ETLs yield the best power conversion efficiency(PCE)of 13.42%.Moreover,a satisfying efficiency of 12.59%has been obtained for the fully-flexible OPVs.As far as we know,this is one of the highest PCE for fully-flexible OPV based PM6:IT-4 F system.More importantly,the flexible OPVs devices can retain more than 80%of its initial efficiency after 5000 bending cycles.Furthermore,among various curvature radii,the mechanical properties of the device based on CPE@PVP are superior to those of the device based on bare CPE as ETL.These findings indicate that the functional flexibility of CPE as a cathode interfacial layer is an effective strategy to fabricate high-performance flexible devices in the near future.

Nitrogen‐doped tin oxide electron transport layer for stable perovskite solar cells with efficiency over 23%

Tin oxide has made a major breakthrough in high-efficiency perovskite solar cells(PSCs)as an efficient electron transport layer by the low-temperature chemical bath deposition method.However,tin oxide often contains pernicious defects,resulting in unsatisfactory performance.Herein,we develop high-quality tin oxide films via a nitrogen-doping strategy for high-efficiency and stable planar PSCs.The aligned energy level at the interface of doped SnO_(2)/perovskite,more excellent charge extraction and reduced nonradiative recombination contribute to the enhanced efficiency and stability.Correspondingly,the power conversion efficiency of the devices based on N‐SnO_(2) film increases to 23.41% from 20.55% of the devices based on the pristine SnO_(2).The N-SnO_(2) devices show an outstanding stability retaining 97.8% of the initial efficiency after steady-state output at a maximum power point for 600s under standard AM1.5G continuous illumination without encapsulation,while less than 50% efficiency remains for the devices based on pristine SnO_(2).This simple scalable strategy has shown great promise toward highly efficient and stable PSCs.

Chlorine-modified SnO2 electron transport layer for high-efficiency perovskite solar cells

A high-quality electron transport layer(ETL)is a critical component for the realization of high-efficiency perovskite solar cells.We developed a controllable direct-contact reaction process to prepare a chlorinated SnO2(SnO2-Cl)ETL.It is unique in that(a)102-dichlorobenzene is used to provide more reactive Cl radicals for more in-depth passivation;(b)it does not introduce any impurities other than chlorine.It is found that the chlorine modification significantly improves the electron extraction.Consequently,its associated solar cell efficiency is increased from 17.01%to 17.81%comparing to the pristine SnO2 ETL without the modification.The hysteresis index is significantly reduced to 0.017 for the SnO2-Cl ETL.

TiO_(2)/SnO_(2)electron transport double layers with ultrathin SnO_(2)for efficient planar perovskite solar cells

The electron transport layer(ETL)plays an important role on the performance and stability of perovskite solar cells(PSCs).Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks.Here,an ultrathin SnO_(2)layer of~5 nm deposited by atomic layer deposit(ALD)was used to construct a TiO_(2)/SnO_(2)double ETL,improving the power conversion efficiency(PCE)from 18.02%to 21.13%.The ultrathin SnO_(2)layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface,promoting charge extraction and transfer.The ultrathin SnO_(2)layer also passivates the ETL/perovskite interface,suppressing nonradiative recombination.The double ETL achieves outstanding stability compared with PSCs with TiO_(2)only ETL.The PSCs with double ETL retains 85%of its initial PCE after 900 hours illumination.Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.

Interface Modification of TiO_(2)Electron Transport Layer with PbCl_(2)for Perovskiote Solar Cells with Carbon Electrode

Perovskite Solar Cells(PSCs)have attracted considerable attention because of their unique features and high efficiency.However,the stability of perovskite solar cells remains to be improved.In this study,we modified the TiO_(2)Electron Transport Layer(ETL)interface with PbCl_(2).The efficiency of the perovskite solar cells with carbon electrodes increased from 11.28%to 13.34%,and their stability obviously improved.The addition of PbCl_(2)had no effect on the morphology,crystal structure,and absorption property of the perovskite absorber layer.However,it affected the band energy level alignment of the solar cells and accelerated the electron extraction and transfer at the interface between the perovskite layer and the ETL,thus enhancing the overall photovoltaic performance.The interfacial modification of ETL with PbCl_(2)is a promising way for the potential commercialization of low-cost carbon electrode-based perovskite solar cells.

Room-temperature synthesis of ZrSnO4 nanoparticles for electron transport layer in efficient planar hetrojunction perovskite solar cells

The interface engineering plays a key role in controlled optoelectronic properties of perovskite photovoltaic devices,and thus the electron transport layer(ETL)material with tailored optoelectronic properties remains a challenge for achieving high photovoltaic performance of planar perovskite solar cells(PSCs).Here,the fine and crystalline zirconium stanate(ZrSnO4)nanoparticles(NPs)was synthesized at low temperature,and its optoelectronic properties are systematically investigated.Benefiting from the favorable electronic structure of ZrSnO4 NPs for applications in ETL,efficient electron transport and extraction with suppre s sed charge recombination are achieved at the interface of perovskite layer.As a result,the optimized ZrSnO4 NPs synthesized at room-temperature deliver the optimized power conversion efficiency up to 16.76%with acceptable stability.This work opens up a new class of ternary metal oxide for the use in ETL of the planar PSCs and should pave the way toward designing new interfacial materials for practical optoelectronic devices.

Pulsed laser deposition of amorphous InGaZnO_(4)as an electron transport layer for perovskite solar cells

Hybrid perovskite solar cells(PSCs)have been intensively studied in recent years because of their high efficiency and low costs.For PSCs,the electron transport layer(ETL)is a key for its photoelectric conversion efficiency.Here we demonstrate the application of amorphous InGaZnO_(4)thin films as ETL for efficient PSCs by pulsed laser deposition(PLD).The PSC device using such InGaZnO_(4)amorphous film as ETL has achieved an efficiency of 15.1%.The outstanding performance is attributed to the excellent properties of amorphous InGaZnO_(4)oxide thin films,including high electron mobility and high transparency,what is more,the electronic properties of the films can be controlled by changing the partial pressure of oxygen in the deposition chamber and post-deposition annealing process.Our result will be helpful for preparation of large area PSCs and other opto-electric devices at low temperature by physical vapor deposition method.

Efficient perovskite solar cells based on the novel low-temperature processed electron transport layer

With the support by the National Natural Science Foundation of China,the research team led by Prof.Hou Yu(侯宇)and Prof.Yang Huagui(杨化桂)at the Key Laboratory for Ultrafine Materials of Ministry of Education,School of Materials Science and Engineering,East China University of Science

ZnO-PCBM bilayers as electron transport layers in low-temperature processed perovskite solar cells

We investigate an electron transport bilayer fabricated at <110 °C to form all low-temperature processed,thermally stable, efficient perovskite solar cells with negligible hysteresis. The components of the bilayer create a symbiosis that results in improved devices compared with either of the components being used in isolation. A sol-gel derived ZnO layer facilitates improved energy level alignment and enhanced charge carrier extraction and a [6,6]-phenyl-C_(61)-butyric acid methyl ester(PCBM) layer to reduce hysteresis and enhance perovskite thermal stability. The creation of a bilayer structure allows materials that are inherently unsuitable to be in contact with the perovskite active layer to be used in efficient devices through simple surface modification strategies.

Materials and structures for the electron transport layer of efficient and stable perovskite solar cells

The electron transport layer plays a vital function in extracting and transporting photogenerated electrons, modifying the interface, aligning the interfacial energy level and minimizing the charge recombination in perovskite solar cells. This review summarizes the recent research progress on electron transport materials of metal oxides, organic molecules and multilayers. The doped metal oxides as electron transport materials in regular perovskite solar cells show improved device performance relative to their non-doped counterpart due to enhanced electron mobility and energy level alignment. The non-fullerene organic electron transport materials with better electron mobility and tunable energy level alignment need to be further designed and developed despite their advantages of mechanical flexibility and wide range tunability. The multilayer electron transport materials are suggested to be an important direction of research for efficient and stable perovskite solar cells because of their favorable synergistic interaction.

Improved performance of organic light-emitting diodes with dual electron transporting layers

In this study the performance of organic light-emitting diodes （OLEDs） are enhanced significantly, which is based on dual electron transporting layers （13phen/CuPc）. By adjusting the thicknesses of Bphen and CuPc, the maximal luminescence, the maximal current efficiency, and the maximal power efficiency of the device reach 17570 cd/m^2 at 11 V, and 5.39 cd/A and 3.39 lm/W at 3.37 mA/cm^2 respectively, which are enhanced approximately by 33.4%, 39.3%, and 68.9%, respectively, compared with those of the device using Bphen only for an electron transporting layer. These results may provide some valuable references for improving the electron injection and the transportation of OLED.