Electron Transport Layer For Perovskite Solar Cells Research Articles

Cross-Linkable Fullerene Electron Transport Layer with Internal Encapsulation Capability for Efficient and Stable Inverted Perovskite Solar Cells.

A stable and compact fullerene electron transport layer (ETL) is crucial for high-performance inverted perovskite solar cells (PSCs). However, traditional fullerene-based ETLs like C60 and PCBM are prone to aggregate under operational conditions, a challenge recently recognized by academic and industrial researchers. Here, we designed and synthesized a novel cross-linkable fullerene molecule, bis((3-methyloxetan-3-yl)methyl) malonate-C60 monoadduct (BCM), for use as an ETL in PSCs. Upon a low-temperature annealing at 100 °C, BCM undergoes in-situ cross-linking to form a robust cross-linked BCM (CBCM) film, which demonstrates excellent electron mobility and a suitable band structure for efficient PSCs. Our results show that PSCs incorporating CBCM-based ETL achieve an impressive efficiency of 25.89% (certified: 25.36%), significantly surpassing the 23.25% efficiency of PCBM-based devices. The intramolecular covalent interactions within CBCM films effectively prevent aggregation and enhance film compactness, creating an internal encapsulation layer that mitigates the decomposition and ion migration of perovskite components. Consequently, CBCM-based PSCs show exceptional stability, maintaining 97.8% of their initial efficiency after 1000 hours of maximum power point tracking, compared to only 78.6% retention in PCBM-based devices after less than 820 hours.

Reduction of recombination at the interface of perovskite and electron transport layer with graded pt quantum dot doping in ambient air-processed perovskite solar cell

The study of charge transfer in thin film solar cells made of several layers is of high importance since they may lose their energy via the recombination process at the interfaces, specifically at the interface of the electron transport layer (ETL) and perovskite. Titanium dioxide (TiO2) is mostly used as an ETL in perovskite solar cells due to its many advantages. However, TiO2 has some disadvantages, such as low electron mobility compared to the perovskite layer and electron trap states on its top at the interface. These effects cause the accumulation of carriers at the ETL/perovskite interface then the non-radiative recombination will be enhanced, which is considered as one of the significant losses in the Perovskite Solar Cells (PSCs). In this work, a new technique is taken for more optimal ETL doping. We fabricated the ETL layers with graded doping of platinum quantum dots (Pt QDs), in which Pt QDs concentration is high at the ETL/Perovskite interface and zero at the FTO/ETL interface. This strategy not only suppresses the recombination at the ETL/perovskite interface and subsequently enhances the device efficiency from 12.92 to 14.36% but also improves the stability of the PSCs.

Influence of the Electron Transport Layer on the Performance of Perovskite Solar Cells under Low Illuminance Conditions.

Owing to the tunable band gap of metal-halide perovskite compounds, perovskite solar cells (PSCs) are promising energy-harvesting devices for indoor applications. Since the electron transport layer (ETL) plays a critical role in the performance of PSCs, selecting a suitable ETL is important for improving the performance of PSCs. Here, we compared the characteristics of PSCs employing TiO2 and SnO2, which are widely used as ETLs in PSCs, under low illuminance conditions. Electrochemical impedance spectroscopy revealed that PSCs employing SnO2 as the ETL exhibited lower charge transfer resistance than those employing TiO2 in low light intensity environments. Consequently, SnO2-based PSCs showed a higher power conversion efficiency of 27.7% than that of TiO2-based PSCs (22.5%) under 1000 lx white LED illumination. Space-charge-limited current measurements have shown that the defect density of ETLs strongly affects the performance of PSCs, especially under low illuminance conditions. We believe that this report provides an effective strategy for selecting appropriate ETLs for indoor applications of PSCs.

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.