Electron Transport Layer For Perovskite Solar Cells Research Articles

Simultaneous Li-Doping and Formation of SnO2-Based Composites with TiO2: Applications for Perovskite Solar Cells.

Tin oxide (SnO2) has been recognized as one of the beneficial components in the electron transport layer (ETL) of lead-halide perovskite solar cells (PSCs) due to its high electron mobility. The SnO2-based thin film serves for electron extraction and transport in the device, induced by light absorption at the perovskite layer. The focus of this paper is on the heat treatment of a nanoaggregate layer of single-nanometer-scale SnO2 particles in combination with another metal-dopant precursor to develop a new process for ETL in PSCs. The combined precursor solution of Li chloride and titanium(IV) isopropoxide (TTIP) was deposited onto the SnO2 layer. We varied the heat treatment conditions of the spin-coated films comprising double layers, i.e., an Li/TTIP precursor layer and SnO2 nanoparticle layer, to understand the effects of nanoparticle interconnection via sintering and the mixing ratio of the Li-dopant on the photovoltaic performance. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) measurements of the sintered nanoparticles suggested that an Li-doped solid solution of SnO2 with a small amount of TiO2 nanoparticles formed via heating. Interestingly, the bandgap of the Li-doped ETL samples was estimated to be 3.45 eV, indicating a narrower bandgap as compared to that of pure SnO2. This observation also supported the formation of an SnO2/TiO2 solid solution in the ETL. The utilization of such a nanoparticulate SnO2 film in combination with an Li/TTIP precursor could offer a new approach as an alternative to conventional SnO2 electron transport layers for optimizing the performance of lead-halide perovskite solar cells.

In situ one step growth of amorphous tin oxide electron transport layer for high-performance perovskite solar cells.

Tin oxide used in electron transport layer (ETL) exhibits key role in transmitting electrons and blocking holes in perovskite solar cells (PSCs) device. However, crystal tin oxide nanoparticles (NPs) become necessary to form SnO2 film by method of spin-coating, resulting in possible surface defect and cracks among SnO2 NPs, corresponding to unsatisfied performance PSCs. Herein, an amorphous tin oxide thin film is creatively in situ grew onto Fluorine-doped Tin Oxide (FTO) substrate as ETL. The designed solar cell device with structure of FTO/SnO2/MAPbI3/Sprio-OMeTAD/Ag owns a champion photoelectric conversion efficiency (PCE) up to 17.64%, 76.20% of filling coefficient (FF), and 1.09 V of open-circuit voltage (Voc), in comparing with 16.43%, 64.35% and 1.05 V for control group (crystal tin oxide as ETL), respectively. Besides, the champion device keeps 83.33% of initial PCE under nitrogen (N2) condition for one month, in comparison with 76.09% for control group. This work provides a viable strategy for facile preparing amorphous tin oxide film based ETL in perovskite solar cells.

Enhancing efficiency and stability of perovskite solar cells through methoxyamine hydrochloride modified SnO2 electron transport layer

Perovskite solar cells (PSCs) hold promise for future photovoltaic applications due to their high performance, low cost, and simple fabrication. The electron transport layer (ETL) plays a crucial role in PSC performance, and tin dioxide (SnO2) has gained attention as a promising ETL candidate. In this study, we investigate the use of methoxyamine hydrochloride (MOACl) as a modifier for SnO2 ETLs in PSCs. MOACl improves the film quality of SnO2, resulting in improved electrical conductivity and electron mobility. MOACl also enhances perovskite crystallization, promoting the growth of larger grain sizes and more uniform film morphology. The enhanced hydrogen bond and migration of Cl within the perovskite layer aids in optimal crystallization and significantly boosts the overall PCE of the cells from 21.67 % to 24.34 %. Moreover, MOACl-SnO2 PSCs demonstrate excellent long-term stability, retaining over 80 % of their initial efficiency after 50 days in ambient air. This work highlights the practical and effective approach of MOACl modification for controlling SnO2 defects and improving perovskite crystallization, paving the way for the development of efficient and stable PSCs.

Exploring the effect of interface properties between CeO x electron transport layer and MAPbI3 perovskite layer on solar cell performances through numerical simulation

Abstract Organo-metal halide perovskite solar cells (PSCs) have received a lot of attention to the photovoltaic research community, mainly due to the rapid development of their cell performances. But industry-level production of PSCs is hindered for several reasons. At present, the use of high-temperature processed electron transport layer (ETL) such as TIO2, the use of chemically unstable ETL such as ZnO and SnO2, etc. are ETL-related obstacles behind this industrialization. Aiming to remove these problems, cerium oxide (CeO x ), one of the most Earth-rich metal oxides has been chosen as ETL for this study. In this study, the SCAPS-1D simulation package has been used for an intensive study on ETL/PSK interface for a methylammonium lead iodide (MAPbI3)-based PSC having CeO x as ETL. From this simulation, the effect of conduction band offset (CBO) between CeO x and MAPbI3 has been found as the key player behind the cell performances. Defects at this interface have also been introduced and varied for studying their effects on cell performance at different CBO values. The temperature stability of a PSC is another important issue that has been considered in this study to find the effect of operating temperature on the PSC. This study would enlighten the researchers in implying some fantastic techniques at the ETL/PSK interface for improving the cell performance that will forward the research community a few steps to use CeO x as a promising ETL in PSC.

Growth and Dispersion Control of SnO2 Nanocrystals Employing an Amino Acid Ester Hydrochloride in Solution Synthesis: Microstructures and Photovoltaic Applications.

Tin oxide (SnO2) is a technologically important semiconductor with versatile applications. In particular, attention is being paid to nanostructured SnO2 materials for use as a part of the constituents in perovskite solar cells (PSCs), an emerging renewable energy technology. This is mainly because SnO2 has high electron mobility, making it favorable for use in the electron transport layer (ETL) in these devices, in which SnO2 thin films play a role in extracting electrons from the adjacent light-absorber, i.e., lead halide perovskite compounds. Investigation of SnO2 solution synthesis under diverse reaction conditions is crucial in order to lay the foundation for the cost-effective production of PSCs. This research focuses on the facile catalyst-free synthesis of single-nanometer-scale SnO2 nanocrystals employing an aromatic organic ligand (as the structure-directing agent) and Sn(IV) salt in an aqueous solution. Most notably, the use of an aromatic amino acid ester hydrochloride salt-i.e., phenylalanine methyl ester hydrochloride (denoted as L hereafter)-allowed us to obtain an aqueous precursor solution containing a higher concentration of ligand L, in addition to facilitating the growth of SnO2 nanoparticles as small as 3 nm with a narrow size distribution, which were analyzed by means of high-resolution transmission electron microscopy (HR-TEM). Moreover, the nanoparticles were proved to be crystallized and uniformly dispersed in the reaction mixture. The environmentally benign, ethanol-based SnO2 nanofluids stabilized with the capping agent L for the Sn(IV) ions were also successfully obtained and spin-coated to produce a SnO2 nanoparticle film to serve as an ETL for PSCs. Several SnO2 ETLs that were created by varying the temperature of nanoparticle synthesis were examined to gain insight into the performance of PSCs. It is thought that reaction conditions that utilize high concentrations of ligand L to control the growth and dispersion of SnO2 nanoparticles could serve as useful criteria for designing SnO2 ETLs, since hydrochloride salt L can offer significant potential as a functional compound by controlling the microstructures of individual SnO2 nanoparticles and the self-assembly process to form nanostructured SnO2 thin films.

Multifunctional Polymer Restraint of the Agglomeration of SnO2 Nanocrystals for Efficient and Stable Planar Perovskite Solar Cells.

The aggregation of SnO2 nanocrystals due to van der Waals interactions is not conducive to the realization of a compact and pinhole-free electron transport layer (ETL). Herein, we have utilized potassium alginate (PA) to self-assemble SnO2 nanocrystals, forming a PA-SnO2 ETL for perovskite solar cells (PSCs). Through density functional theory (DFT) calculations, PA can be effectively absorbed onto the surface of SnO2. This inhibits the agglomeration of SnO2 nanocrystals in solution, forming a smoother pinhole-free film. This also changes the surface contact potential (CPD) of the SnO2 film, which leads to a reduction in the energy barrier between the ETL and the perovskite layers, promotes effective charge transfer, and reduces trap density. Consequently, the power conversion efficiency (PCE) of PSCs with a PA-SnO2 ETL increased from 19.24% to 22.16%, and the short-circuit current (JSC) was enhanced from 23.52 to 25.21 mA cm-2. Furthermore, the PA-modified unpackaged device demonstrates better humidity stability compared to the original device.

Applications of Ba doped rutile TiO2 nanorod arrays in carbon-based all-inorganic perovskite solar cells

The electron transport layer (ETL) plays an important part in perovskite solar cell (PSC) devices. TiO2 nanorod arrays (TiO2 NAs) is widely used as ETL for perovskite solar cells because of its excellent energy level matching. Furthermore, TiO2 NAs provide the directed 1-D electron transmission channel. In this work, rutile TiO2 NAs synthesized by one-step hydrothermal method were used as the ETL of carbon-based perovskite solar cells to improve the performance. The interface between the ETL and perovskite was modified by barium acetate to reduce interface defects, non-radiative recombination and improve the electron transport rate. The perovskite film based on the Ba@TiO2 NAs exhibited larger grains and fewer grain boundaries, which was of positive significance for improving the power conversion efficiency (PCE) of devices. At the same time, we replaced the precious metal electrode and unstable organic hole transport layer (HTL) with carbon electrode, which reduces the manufacturing cost and improves the stability of the device. Finally, all inorganic HTL-free carbon-based perovskite solar cells based on Ba@TiO2 NAs showed a champion PCE of 10.74%, which is 14.74% higher than the control device.

Recent Advances of Doped SnO2 as Electron Transport Layer for High-Performance Perovskite Solar Cells.

Perovskite solar cells (PSCs) have garnered considerable attention over the past decade owing to their low cost and proven high power conversion efficiency of over 25%. In the planar heterojunction PSC structure, tin oxide was utilized as a substitute material for the TiO2 electron transport layer (ETL) owing to its similar physical properties and high mobility, which is suitable for electron mining. Nevertheless, the defects and morphology significantly changed the performance of SnO2 according to the different deposition techniques, resulting in the poor performance of PSCs. In this review, we provide a comprehensive insight into the factors that specifically influence the ETL in PSC. The properties of the SnO2 materials are briefly introduced. In particular, the general operating principles, as well as the suitability level of doping in SnO2, are elucidated along with the details of the obtained results. Subsequently, the potential for doping is evaluated from the obtained results to achieve better results in PSCs. This review aims to provide a systematic and comprehensive understanding of the effects of different types of doping on the performance of ETL SnO2 and potentially instigate further development of PSCs with an extension to SnO2-based PSCs.

Regulating Lewis Acid‐Base Interactions to Enhance Stability of Tin Oxide for High‐Performance Perovskite Solar Cells

AbstractPerovskite solar cells are an attractive technology for renewable energy production. However, stability issues with the electron transport layer (ETL), particularly the colloidal tin oxide (SnO2) solution, can impact cell efficiency. In this study, a novel acidization treatment is introduced to reactivate long‐time stored SnO2 solutions, which previously led to low‐efficiency perovskite solar cells. The acidization treatment results in enhanced conductivity of the SnO2 layer, improved perovskite film quality, and ultimately increased efficiency. These findings show that a 1‐month stored SnO2 solution treated with acetic acid produces a device with a photoelectric conversion efficiency (PCE) of 20.9%, compared to 13.5% efficiency without treatment. With the addition of PEAI, the champion efficiency of the acetic acid‐treated device is 22.3%. This study provides a simple and effective engineering approach to fabricating high‐performance and stable ETLs for perovskite solar cells.

A high-performance perovskite solar cell with a designed nanoarchitecture and modified mesoporous titania electron transport layer by zinc nanoparticles impurity

In this study, the fabrication of perovskite solar cells (PSCs) satisfying both high efficiency and photostability of the PSCs through introducing the zinc nanoparticles into mesoporous titania electron transport layer (ETL) was performed. A soft-template sol–gel method was utilized to prepare different content of Zn dopant in ETL of PSCs. Doping zinc nanoparticles into a mesoporous titania ETL was employed to improve solar cell performance. The results showed that the PSC efficiency of the cell was increased by doping 2 mol% zinc to the mesoporous titania ETL from 9.74 % to 13.76 %. The Voc and Jsc values of 0.98 and 24.44 were achieved for 2 % zinc-doped ETL solar cells. This research focuses on promising perovskite solar cells that combine the large surface area of a mesoporous titania electron transparent layer with zinc oxide nanoparticles to produce solar cells with large applications and rapid cost reductions.

Design of SnO2 Electron Transport Layer in Perovskite Solar Cells to Achieve 2000 h Stability Under 1 Sun Illumination and 85 °C

AbstractIn order to realize both efficient and stable perovskite solar cells, designing electron transport layer (ETL) is of crucial importance to withstand constant light illumination and thermal stress while maintaining high charge extractability. Herein, commonly used SnO2 nanoparticle‐based ETL for perovskite solar cells is modified by ionic‐salt ammonium chloride (NH4Cl) and tin chloride dihydrate (SnCl2∙2H2O) as additives, which is easily fabricated by simple one‐step spin coating of single precursor solution. With the presence of these dual additives at the ETL, the crystallinity of the upper perovskite layer is clearly enhanced. Defect analyses on the devices suggest that these modifications can effectively passivate trap sites that reside within the ETL and at the perovskite interfaces with the carrier‐transport layers. As a result, the modified SnO2 ETL results in an improvement of device stability under thermal or light stress condition, maintaining over 80% of its initial efficiency after ≈2000 h storage under elevated temperature (85 °C) and after ≈2400 h of operation under 1 sun illumination.

Well-organized SnO2 inverse opal monolayer as structured electron transport layer for high-efficiency perovskite solar cells

In mesoporous perovskite solar cells (mp-PSCs), an electron transport layer (ETL) plays an important role in charge extraction and transportation, and also its structure largely affects the crystallization and optical property of perovskite films. At present, the performance of PSCs based mesoporous SnO2 (mp-SnO2) still lags behind that based planar SnO2 due to problems in the fabrication process of mp-SnO2. Herein, a well-organized monolayer SnO2 inverse opal (SIO) is prepared as the structured ETL for perovskite solar cells. The unique periodic SIO structure exhibits an obvious optical coupling phenomenon, which enhances the light absorption of the perovskite layer. Furthermore, the well-organized SIO structure with appropriate pore size triggers the confined crystallization of perovskite films and optimizes the interface of SnO2/perovskites, suppressing the interfacial electron–hole recombination. As a result, the power conversion efficiency of mp-PSCs fabricated by the monolayer SIO is boosted from 19.63% to 22.01%. This work provides a creative strategy for construction of high-efficiency mp-PSCs based on SnO2.

Iodine-doped g-C3N4 modified zinc titanate electron transporting layer for highly efficient perovskite solar cells

The development of excellent ternary metal oxides as electron transporting layers (ETLs) is highly challenging for perovskite solar cells (PSCs). In this study, ZnTiO3 (ZTO) nanoparticles are synthesized via a facile sol-gel method, and used as an ETL in PSCs. Furthermore, for the first time, iodine-doped g-C3N4 (ICN) is introduced into ZnTiO3-based ETL as additive via a glass-assisted annealing route. Characterizations demonstrate that the ZnTiO3-based ETL with the addition of ICN will enhance the PCE, which is attributed to the improved crystalline quality and more favorable energy level alignment. Moreover, the existence of ICN will strengthen the interfacial cohesion between perovskite layer and ETL as well as retard the perovskite crystals from decomposing, leading to the high quality capping light-harvesting layer upon ICN-modified ZnTiO3 (ZTO-ICN) film. Consequently, a champion device fabricated with ZTO-ICN ETL achieves a maximum PCE of 19.17 % with an open circuit voltage (Voc) of 1.012 V, a short-circuit current density (Jsc) of 26.32 mA cm−2 and a fill factor (FF) of 0.720 under AM 1.5 G sunlight (100 mW cm−2).

A Stable Aqueous SnO2 Nanoparticle Dispersion for Roll-to-Roll Fabrication of Flexible Perovskite Solar Cells

Perovskite solar cells (PSCs) are attracting increasing commercial interest due to their potential as cost-effective, lightweight sources of solar energy. Low-cost, large-scale printing and coating processes can accelerate the development of PSCs from the laboratory to the industry. The present work demonstrates the use of microwave-assisted solvothermal processing as a new and efficient route for synthesizing crystalline SnO2 nanoparticle-based aqueous dispersions having a narrow particle size distribution. The SnO2 nanoparticles are analyzed in terms of their optical, structural, size, phase, and chemical properties. To validate the suitability of these dispersions for use in roll-to-roll (R2R) coating, they were applied as the electron-transport layer in PSCs, and their performance was compared with equivalent devices using a commercially available aqueous SnO2 colloidal ink. The devices were fabricated under ambient laboratory conditions, and all layers were deposited at less than 150 °C. The power conversion efficiency (PCE) of glass-based PSCs comprising a synthesized SnO2 nanoparticle dispersion displayed champion levels of 20.2% compared with 18.5% for the devices using commercial SnO2 inks. Flexible PSCs comprising an R2R-coated layer of synthesized SnO2 nanoparticle dispersion displayed a champion PCE of 17.0%.

Nanophotonic-structured front contact for high-performance perovskite solar cells

We report the design of a nanophotonic metal-oxide front contact aimed at perovskite solar cells (PSCs) to enhance optoelectronic properties and device stability in the presence of ultraviolet (UV) light. High-quality Cr-doped ZnO film was prepared by industrially feasible magnetron sputter deposition for the electron transport layer of PSCs. As a means, the influence of the Cr content on the film and device was systematically determined. In-depth device optics and electrical effects were studied using advanced three-dimensional opto-electrical multiphysics rigorous simulations, optimizing the front contact for realizing high performance. The numerical simulation was validated by fabricating PSCs optimized to reach high performance, energy conversion efficiency (ECE) = 17.3%, open-circuit voltage (VOC) = 1.08 V, short-circuit current density (JSC) = 21.1 mA cm−2, and fill-factor (FF) = 76%. Finally, a realistic front contact of nanophotonic architecture was proposed while improving broadband light absorption of the solar spectrum and light harvesting, resulting in enhanced quantum efficiency (QE). The nanophotonic PSC enables JSC improvement by ∼17% while reducing the reflection by 12%, resulting in an estimated conversion efficiency over 23%. It is further demonstrated how the PSCs’ UV-stability can be improved without considerably sacrificing optoelectronic performances. Particulars of nanophotonic designed ZnO:Cr front contact, PSCs device, and fabrication process are described.

Fabrication of SnO2 by RF magnetron sputtering for electron transport layer of planar perovskite solar cells

The requirements of electron transport layer (ETL) for high efficiency Perovskite solar cells (PSCs) are, for example, appropriate band energy alignment, high electron mobility, high optical transmittance, high stability, and easy processing. SnO2 has attracted more attention as ETL for PSCs because it has diverse advantages, e.g., wide bandgap energy, excellent optical and chemical stability, high transparency, high electron mobility, and easy preparation. The SnO2 ETL was fabricated by RF magnetron sputtering technique to ensure the chemical composition and uniform layer thickness when compared to the use of chemical solution via spin-coating method. The RF power was varied from 60 - 150 W. The Ar sputtering gas pressure was varied from 1 × 10−3 - 6 × 10−3 mbar while keeping O2 partial pressure at 1 × 10−4 mbar. The thickness of SnO2 layer decreases as the Ar gas pressure increases resulting in the increase of sheet resistance. The surface morphology and optical transmission of the SnO2 ETL were investigated. It was found that the optimum thickness of SnO2 layer was approximately 35 - 40 nm. The best device shows Jsc = 27.4 mA/cm2, Voc = 1.03 V, fill factor = 0.63, and efficiency = 17.7%.

Reactive thermal evaporated amorphous tin oxide fabricated at room temperature and application in perovskite solar cells

AbstractTin oxide (SnOx) as a functional layer, such as electron transport layer (ETL) or buffer layer, is widely used in perovskite solar cells (PSCs). However, SnOx prepared by spin coating is not suitable to be applied to the solar cells with large area or rough substrates. In this paper, SnOx thin films served as the ETL of PSCs were prepared using a simple reactive thermal evaporation (RTE) method, and a convenient ultraviolet ozone treatment (UV‐O3) at room temperature was carried out to replace the common post‐annealing process. The SnOx ETL prepared by RTE is suitable for substrates with arbitrary morphology, and the performance of the PSCs can be improved significantly after the ultraviolet ozone treatment of the SnOx layer. A power conversion efficiency (PCE) up to 20.62% was achieved on the planar PSCs with the RTE SnOx serving as the ETL. Conformal coverage of the RTE SnOx thin film and the perovskite layer on a textured Si surface was achieved, which is helpful for making fully textured monolithic perovskite/silicon tandem solar cells in the future.

Plasma Oxidized Ti3C2Tx MXene as Electron Transport Layer for Efficient Perovskite Solar Cells.

Recently, the two-dimensional material Ti3C2Tx MXene has attracted interest from researchers in perovskite solar cells (PSCs) with its great advantages in terms of high transmittance, high conductivity, tunable work function, and solution processability. However, the MXene-based PSC performance has still been inferior to that of the traditional TiO2- or SnO2-based counterpart up until now. Some critical issues regarding to the MXene/perovskite interface still have not been well addressed. Herein, we used the Ti3C2Tx MXene as electron transport layer in PSCs via a room-temperature solution process followed by oxygen plasma treatment. Various characterization techniques were taken to establish the correlation between the surface properties and termination groups of MXene. We showed that oxygen plasma treatment could break parts of Ti-C bonds and generate abundant Ti-O bonds randomly distributed on MXene. The surface modification resulted in tunable work functions of MXene, as well as reduced trap states and improved electron transport close to the interface. In addition, the surface tension of MXene and corresponding perovskite morphology were thoroughly investigated by the contact angle and topography measurements. High-resolution XPS spectra indicated the Pb-O interactions between perovskite and MXene, which contributed to the device stability improvement.

Incorporation of Zr-doped TiO2 nanoparticles in electron transport layer for efficient planar perovskite solar cells

Organic–inorganic perovskite solar cells (PSC) are gaining widespread recognition due to their higher performances and low-cost relative to other photovoltaic technologies. However, the efficient charge collection and rapid electron transportation are the key parameters desirable for the development of optimized electron transport layer (ETL) in PSC. In this research work, hydrothermally synthesized zirconium-doped titania nanoparticles (Zr-TiO2) were introduced as an ETL in a n–i–p planar configuration. The Zr-doped TiO2 nanoparticles were characterized for various morphological, structural and optical studies by using SEM, EDX, XRD, Raman, PL and UV-Vis spectroscopy techniques. The photocatalytic activity of newly synthesized Zr-TiO2 nanoparticles was investigated by CV, EIS and tafel measurements. The current–voltage characteristics (J-V) of the newly fabricated PSC devices were investigated under 1 sun condition. The superior power conversion efficiency (PCE) of 12.35 % was observed with 0.2 M Zr-doped TiO2 based ETL in PSC. The remarkable PCE in 0.2 M Zr-doped TiO2 nanoparticles-based PSC is attributed to significant enhancement in charge carrier extraction and due to less recombination reactions at interfaces.

Dip coated SnO2 film as electron transport layer for low temperature processed planar perovskite solar cells

Perovskite solar cells (PSCs) made their mark in the photovoltaic research community due to their accelerating efficiencies, bandgap tunability, ease of fabrication, choice of substrates, etc. The electron transport layer (ETL) plays a decisive role in determining the performance and scalability of PSCs. SnO2 is a potential candidate for ETL in PSCs due to its high transmittance, low sintering temperatures, and suitable deep conduction and valence band positions that allows efficient electron extraction at the interfaces. In this work, we developed a simple, solution-processable low-temperature deposition of SnO2 on fluorine-doped tin oxide (FTO) glass substrates employing dip-coating technique for the first time. The number of dipping cycles are optimized to attain uniform coverage of the SnO2 layer on FTO. Formamidinium lead tri-iodide (FAPbI3) perovskite is deposited onto the dip-coated SnO2 electrode by vapor assisted solution process. XRD reveals the successful SnO2 phase formation by a low-temperature dip-coating method and FAPbI3 perovskite film formation by vapor assisted solution process with an unremarkable presence of the photo inactive δ phase. The surface morphology of the FAPbI3 films is smooth with an average grain size of 220 nm. A preliminary study on the planar device's photovoltaic performance using CuSCN as hole transport material (HTM) and Au as back contact exhibited a power conversion efficiency of 3.2% using four deposition cycles of SnO2 by dip-coating as the electron transport layer. This study demonstrates the utilization of dip-coating as a cost-effective method to deposit ETL that paves the way for PSCs' scale-up.