Layer For Perovskite Solar Cells Research Articles

Unveiling and Modulating the Interfacial Reaction at the Metal-Hole Conductor Heterojunction toward Reliable Perovskite Solar Cells.

Interfaces between functional layers in perovskite solar cells (PSCs) are of paramount importance in determining their efficiency and stability, but the interaction and stability of metal-hole conductor (HC) interfaces have received less attention. Here, we discover an intriguing transient behavior in devices which induces a profound efficiency fluctuation from 9 to 20% during the initial performance testing. Air exposure (e.g., oxygen and moisture) can significantly accelerate this nonequilibrium process and simultaneously enhance the device maximal efficiency. Structural analysis reveals that the chemical reaction between Ag and HC occurred during the metal deposition by thermal evaporation, leading to the formation of an insulating barrier layer at their interfaces, which results in a high charge-transport barrier and poor device performance. Accordingly, we propose a metal diffusion-associated barrier evolution mechanism to understand the metal/HC interfaces. To mitigate these detrimental effects, we strategically develop an interlayer strategy by introducing an ultrathin layer of molybdenum oxide (MoO3) between Ag and HC, which is found to effectively suppress the interfacial reaction, yielding highly reliable PSCs with instant high efficiency. This work provides new insights into understanding the metal-organic interfaces, and the developed interlayer strategy can be generally applicable to engineer other interfaces in realizing efficient and stable contacts.

Solution processable polypyrrole nanotubes as an alternative hole transporting material in perovskite solar cells

The major challenge towards the commercialization of perovskite solar cells is to find an alternative stable, low-cost, and solution-processible hole transporting material to unstable and expensive 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenylamine)− 9,9’- spirobifluorene. Despite having all prerequisite properties like the ease of synthesis, low cost, tunability of hole conductivity, the conducting polymers such as polypyrrole are hardly being explored extensively as hole-transporting materials because of their insolubility in common organic solvents. Here, a colloidal solution of hydrophobic polypyrrole nanotubes co-doped with sodium dodecylbenzenesulfonate has been developed and explored for the hole transporting layer in methylammonium lead iodide-based perovskite solar cells. The best device has shown a power conversion efficiency of 7.3% at ambient conditions and without sealing. In terms of stability, the unsealed polypyrrole-based devices maintaining 85% of the initial efficiency at relative humidity 75–80 % with over 120 h have outperformed the unencapsulated poly(3-hexylthiophene)- based devices (average power conversion efficiency ∼11 %) fabricated using the same procedure and measured under same conditions. Frequency response analysis and electroluminescent imaging reveal that the photovoltaic performance of the polypyrrole-based cells can further be improved by reducing series resistance arising due to hole transporting layers. These studies show the polypyrrole colloids as a promising low-cost solution for the hole transporting layer in perovskite solar cells.

Numerical Investigation of Power Conversion Efficiency of Sustainable Perovskite Solar Cells

Perovskite solar cells have been researched for high efficiency only in the last few years. These cells could offer an efficiency increase of about 3% to more than 15%. However, lead-based perovskite materials are very harmful to the environment. So, it is imperative to find lead-free materials and use them in designing solar cells. This research investigates the potential for using a lead-free double-perovskite material, La2NiMnO6, as an absorbing layer in perovskite solar cells to enhance power conversion efficiency (PCE). Given the urgent need for environmentally friendly energy sources, the study addresses the problem of developing alternative materials to replace lead-based perovskite materials. Compared to single-perovskite materials, double perovskites offer several advantages, such as improved stability, higher efficiency, and broader absorption spectra. In this research work, we have simulated and analyzed a double-perovskite La2NiMnO6 as an absorbing material in a variety of electron transport layers (ETLs) and hole transport layers (HTLs) to maximize the capacity for high-efficiency power conversion (PCE). It has been observed that for a perovskite solar cells with La2NiMnO6 absorbing layer, C60 and Cu2O provide good ETLs and HTLs, respectively. Therefore, the achieved power conversion efficiency (PCE) is improved. The study demonstrates that La2NiMnO6, as a lead-free double-perovskite material can serve as an effective absorbing layer in perovskite solar cells. The findings of this study contribute to the growing body of research on developing high-efficiency, eco-friendly perovskite solar cell technologies and have important implications for the advancement of renewable energy production.

Nanopillar arrays of mesoporous Bi2Se3 and CuInSe2 in layer‐based perovskite solar cells

AbstractThe improvement of light trapping inside the active layer of perovskite solar cells (PSCs) was numerically investigated. The light absorption probability was improved by incorporating periodic arrays of mesoscopic electron‐transporting layer into the absorber layer (CH3NH3PbI3) of the PSCs. Accordingly, chalcopyrite (CuInSe2) and bismuth selenide (Bi2Se3) were introduced in the form of hexagonal pillars with an optimum radius of 35 nm and a height of 292 nm. It was found that the proposed PSCs can significantly extend the broadband light absorption from the visible spectrum to the near‐infrared (NIR) region compared to planar PSCs that have an identical active layer thickness. After optimization, the PSCs based on MP‐CuInSe2 and MP‐Bi2Se3 showed the best performance with an enhancement of respectively 32% and 54 % in the photocurrent density, (with values of 29.94 and 34.93 mA.cm−2), as compared to the planar PSC (with a photocurrent density of 22.69 mA.cm−2). This enhancement resulted from a more effective carrier transport due to the mesoscopic structures.

Compact TiO2 layer by UV-assisted TiBr4 chemical bath deposition for perovskite solar cells

A new method to prepare a compact TiO2 layer for perovskite solar cells is introduced. The method features a UV-assisted chemical bath in an aqueous TiBr4 solution. The process does not require sophisticated systems to implement making scaling-up easy and the precursor ensures a uniform TiO2 layer with densely-packed planar grains. UV light provides an alternative to the temperature-assisted CBD process and eliminates the necessity to stir the solution during a deposition that opens new horizons for further scaling up PSCs. The new compact layer was compared to the spin-coated TiO2 layer and it was found that the novel method allows obtaining a more uniform layer with conformal coverage of the substrate. The new TiO2 layer was tested for perovskite solar cells and showed an improvement in open-circuit voltage (VOC) which can be explained by improved morphology and surface coverage of the TiO2 layer.

Synthesis and characterization of N,N′-Di-1-naphthyl-N,N′-diphenylbenzidine as a hole-transporting layer (HTL) for Perovskite solar cell applications

In this communication, we report a typical structural, optical and electrical analysis of thin films of hole transport material (HTM) based on aromatic phenyl benzidine derivative (N,N[Formula: see text]-Di-1-naphthyl-N,N[Formula: see text]-diphenylbenzidine) deposited by thermal evaporation technique onto the glass substrate. The effect of substrate temperature on the physical and electronic properties of these organic thin films for perovskite solar cells (PSCs) applications has been investigated. The films have been characterized by FTIR, XRD, SEM, UV–Vis spectroscopy and photoluminescence spectroscopy. Electrical conductivity and activation energies of films have also been calculated. From FTIR data of fabricated films and powder, it was found that the compound does not decompose during the thermal evaporation process as observed vibrational frequencies of films and the powder are the same. From the results, it has been determined that the substrate temperature has a huge impact on the physical structure and has also influenced the optical, electrical properties of the films. As observed from the studies it appears that these amorphous films with bandgap near to 3[Formula: see text]eV and suitable conductivity have potential for photovoltaics layer devices. From this study, it can be concluded that N,N[Formula: see text]-Di-1-naphthyl-N,N[Formula: see text]-diphenylbenzidine can be used as an active hole transport layer in PSCs.

Enhanced performance of inverted hybrid perovskite solar cells with interfacial passivation filler

Defects at the interface between the perovskite and charge transport layers in perovskite solar cells serve as sites for non-radiative charge recombination as they are the main energy loss channels that reduce the open-circuit voltage. In this study, we used a small molecule, N-methyl-4-piperidone (NMPD), as an interfacial passivation filler between the perovskite and electron transport layers in inverted organic–inorganic hybrid CH3NH3PbI3 perovskite solar cells. The filler deactivates the charge traps at the interface, which are responsible for non-radiative charge recombination, and improves the electron extraction efficiency. Consequently, it enhanced the power conversion efficiency (PCE) from 16.3% to 20.1% by increasing both the open-circuit voltage and short-circuit current. Furthermore, after 800 h of aging without encapsulation at 35% humidity and 25 °C temperature, the device with NMPD filler retained 78.4% of the initial PCE. This indicates that the interfacial modification filler, with a single carbonyl group, can effectively improve the efficiency as well as the stability of perovskite devices.

Recent Progress in Perovskite Solar Cells: Status and Future

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has seen effective performance upgrades, showing remarkable academic research and commercial application value. Compared with commercial silicon cells, the PCE gap is narrowing. However, the stability, cost, and large-scale production are still far behind. For scale-up preparing high-efficiency and stable PSCs, there is a variety of related research from each functional layer of perovskite solar cells. This review systematically summarizes the recent research on the functional layers, including the electron transport layer, perovskite layer, hole transport layer, and electrode. The common ETL materials, such as TiO2, SnO2, and ZnO, need doping and a bi-layer ETL to promote their property. Large-scale and low-cost production of perovskite layers with excellent performance and stability has always been the focus. The expensive and instability problems of Spiro-OMeTAD and electrode materials remain to be solved. The main problems and future development direction of them are also discussed.

Metal-Organic Framework Materials in Perovskite Solar Cells: Recent Advancements and Perspectives.

Organic-inorganic hybrid perovskite solar cells (PSCs) are among the most promising candidates for the next generation of photovoltaic devices because of the significant increase in their power conversion efficiency (PCE) from less than 10% to 25.7% in past decade. The metal-organic framework (MOF) materials owing to their unique properties, such as large specific surface area, abundant binding sites, adjustable nanostructures, and synergistic effects, are used as additives or functional layers to enhance the device performance and long-term stability of PSCs. This review focuses on the recent advancements in the applications of MOFs as/in different functional layers of PSCs. The photovoltaic performance, impact, and advantages of MOF materials integrated into the perovskite absorber, electron transport layer, hole transport layer, and interfacial layer are reviewed. In addition, the applicability of MOFs to mitigate leakage of Pb2+ from halide perovskites and corresponding devices is discussed. This review concludes with the perspectives on further research directions for employing MOFs in PSCs.

Printing‐Induced Alignment Network Design of Polymer Matrix for Stretchable Perovskite Solar Cells with Over 20% Efficiency

AbstractPolymer matrix is felicitously applied into the active layer and transporting layer of perovskite solar cells (PSCs) to enable a stretchable function. However, the chaotic deposition of polymer chains is the main cause for the inferior photoelectric performance. When the stretchable PSCs are in a working state, the stress cannot be removed effectively due to the random polymer chain deposition. The stress accumulation will cause irreversible damage to the stretchable PSCs. Herein, the structural bionics and patterned‐meniscus coating technology are combined to print the polymer chain‐oriented deposition in the stretchable PSCs. Based on this approach, the conducting polymer electrode is printed with both significant mechanical stability and conductivity. More importantly, the oriented polyurethane with self‐healing property can enhance the crystal quality of perovskite films and repair perovskite cracks caused by stress destruction. Thus, the corresponding stretchable PSCs achieve a stabilized power conversion efficiency (PCE) of 20.04% (1.0 cm2) and 16.47% (9 cm2) with minor efficiency discrepancy. Notably, the stretchable PSCs can maintain 86% of the primitive PCE after 1000 cycles of bending with a stretch ratio of 30%. This directional growth of polymer chain strategy provides guidance for printing prominent‐performance stretchable PSCs.

A novel natural scaffold layer improving efficiency, stability and reproducibility of Perovskite solar cells

In this study, our hypothesis was to demonstrate the usability of a natural clay structure as scaffold layer in perovskite solar cells (PSCs). Sepiolite, which is a natural and environmentally friendly clay structure, has a very high active surface area and can easily be dispersed in solvents. In addition we predicted that crystallization could easily occur on their surfaces due to their surface chemistry. In the study, we firstly used a natural clay as scaffold layer in PSCs. It is observed that, efficiency, reproducibility and stability of PSCs have been significantly improved. Improvements in efficiency have been observed to be between 30 and 50% depending on the type of perovskite solvent used. In addition, the surface chemistry of the sepiolite resulted in better crystallization as well as stability. Due to its high-water adsorption capability, sepiolite makes the perovskite crystal more stable by trapping the residual water molecules as well as penetrated water molecules from environment. Consequently, we demonstrated that, a natural, low-cost and environmentally friendly clay may be an alternative material which may contribute to the commercialization of PSCs.

Multilayer conformal structural perovskite solar cells design for light trapping enhancement

Thin film perovskite solar cells (PSCs) have insufficient light utilization due to thickness limitation. Structural design of thin film PSCs can effectively enhance the property of light trapping and thereby improve the photocurrent density. In this work, both the thickness of perovskite layer and front Indium Tin Oxides (ITO) layer for classical PSCs was firstly optimized. 22.4% of light absorption enhancement can be achieved. Then, we proposed four different types of multilayer conformal structures PSCs consisting of hemisphere, cylinder, inverted pyramid and cone structures. Compared with the planner PSCs, the optimized hemispherical multilayer conformal structure (HMCS) PSCs can further enhance the light absorption by 12.3% and obtain the highest photocurrent density of 23.82 mA/cm−2. The photonic interaction between the structure and incident wavelength is examined and discussed. The presented method and multilayer conformal structures can be used to design the light absorption enhancement for a variety of PSCs.

Effect of Oxygen Vacancy on the Crystallinity and Optical Band Gap in Tin Oxide Thin Film

Herein, we have prepared tin oxide (SnO2) nanoparticles (NPs), through a co-precipitation method, using SnCl2·2H2O dissolved in distilled water (DW) as a precursor. Then, the prepared NPs were heat treated in a muffle furnace, as a function of temperature, under an open atmosphere. The prepared SnO2 NPs were then re-dispersed in DW, followed by spray casting on a glass substrate, for preparing SnO2 thin films. The average thickness of the fabricated SnO2 thin films was 2.76 µm. We demonstrated a very clear variation in the structural, compositional, and morphological features of the different films (in particular, variation of the density of oxygen vacancies), which altered their electrical and optical properties. Raising the calcination temperature of the SnO2 thin films, from 250 °C to 650 °C, led to a monotonic reduction in the crystallite size, from 10.4 nm to 6.7 nm, and a decrease in the O/Sn ratio, from 5.60 to 4.79. A 14.5% decrease in the O/Sn ratio resulted in a decrease in the crystallite size by 3.7 nm (i.e., a 35.3% decrease in the NP size), and a decrease in the band gap of 0.11 eV. The lowering of the band gap, along with an increase in the oxygen vacancies in the films, accords well with previous studies. Besides, as the calcination temperature was raised, the refractive index and absorption coefficient values were also found to notably increase. Very interestingly, by simply altering the calcination temperature, we were able to produce SnO2 thin films with optical band gaps nearly equal to the fundamental band gap (2.96 eV), even though many earlier experimental studies had reported considerably greater values (3.36–4.24 eV). SnO2 thin films with lower oxygen vacancies exhibited relatively higher band gaps, which is likely to be favorable for the desired electron transport layer in perovskite solar cells.

Slot-Die-Coated Active Layer for Printed Flexible Back-Contact Perovskite Solar Cells

Perovskites have already shown potential as active layers in photovoltaic applications. Furthermore, a low-cost and simple solution processing technology allows perovskites to be used in flexible and printed electronics. Perovskite solar cells (PSC) with a back-contact (BC) structure, in which the electrode system is based on a quasi-interdigitated back-contact (QIBC) design, promise to increase the power conversion efficiency (PCE) of devices beyond those that can be obtained using PSCs with a traditional sandwich structure. While the spin-coating technique is used to deposit the perovskite layer of lab-scale BC PSCs, the application of large-area printing techniques to deposit the perovskite layer of such devices is yet to be explored. Therefore, this work demonstrates an application of the slot-die coating technique to print the perovskite active layer of BC PSCs with QIBC electrodes on flexible polymer substrates. The morphology of the obtained perovskite films on QIBC electrodes are investigated and the primary photoelectric parameters of the resulting BC PSCs are measured. The charge carrier recombination processes in the fabricated BC PSCs are investigated and the dominant mechanism for carrier loss in the devices is determined. The findings of the work give an insight into the properties of the slot-die-coated perovskite active layer of BC PSCs and points to exciting new research opportunities in this direction.

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.

Effect of the TiO2 electron transport layer thickness on charge transfer processes in perovskite solar cells

Dense TiO2 thin films are widely used as electron transport layers in perovskite solar cells. TiO2 is a high band gap semiconductor with n-type conductivity showing excellent compatibility with metal-halide perovskites in terms of energy alignment providing efficient charge separation and less energy loss of electrons during electron transfer. In this work, TiO2 layers were deposited from TiO2 sol-gel solution by spin-coating methods. The optimization of TiO2 ETL thickness is a necessary procedure to reduce ETL resistance and minimize charge recombination. The thickness reduction leads to a decrease in resistance, however, also enhances charge recombination due to the formation of pin-holes and cracks. We found that TiO2 thickness reduction also causes the TiO2 defects density changes. By studying luminescence spectra of TiO2 with various thicknesses we found that the thickness reduction leads to the increase in the interstitial Ti+3 defects density, while the oxygen vacancies density decreases. Ti+3 species form deep levels trapping free electrons and as result increasing TiO2 resistance. TiO2 films with thicknesses in the range of 40–120 nm were deposited and used as ETL for PSCs with ITO/TiO2/CH3NH3I3PbClx/CuPc/MoOx/Ag structure. Our study revealed two competitive charge transport processes taking place in TiO2: electron transport through the TiO2 conduction band and electron trapping by deep trap levels formed by Ti+3 species. Therefore according to the IV and IS studies, the optimal TiO2 layer thickness at which there is a balance between the competitive charge transport processes is about 60 nm for our deposition condition.

Two Birds with One Stone: Dual‐Functional Difluorinated Modifier Enabling Efficient and Stable Perovskite Solar Cells

The interface between the perovskite layer and charge transport layer (CTL) plays an important role in the photoelectric conversion of perovskite solar cells (PSCs). In essence, the presence of defects and unideal contact at the perovskite/CTL interface induces severe nonradiative charge recombination, thus limiting the open‐circuit voltage and fill factor of PSCs. Herein, a two‐birds‐with‐one‐stone strategy to overcome the earlier challenges is reported, in which a single reagent 3,5‐difluorobenzenesulfonamide (3,5‐DFBS) is applied as an interface modifier between perovskite layer and spiro‐OMeTAD hole transport layer (HTL) in conventional PSCs. The 3,5‐DFBS molecules can passivate the undercoordinated Pb2+‐related surface defects by forming coordination through SO group and simultaneously strengthen the perovskite/HTL interface contact via F–π interactions, thus promoting hole extraction greatly. As a result, a champion efficiency of 23.69% with substantially improved stability is accomplished for 3,5‐DFBS PSCs. This work demonstrates that the two‐birds‐with‐one‐stone strategy is promising for achieving highly efficient and stable PSCs.

High Charge Transfer from C60 Pyrrolidine Tris-Acid to SnO2 Electron Transport Layer Directly Observed by ESR Spectroscopy

Charge transfer characteristics of perovskite solar cells (PSCs) are effectively modified using fullerene-passivated SnO2 electron transport layers (ETLs), which are used as electron injection components from the perovskite layer in PSCs. Characterizing the charge accumulation states of decisive scientific evidence is highly expected. Therefore, to investigate the charge accumulation states over time from a microscopic viewpoint, this study presents electron spin resonance (ESR) spectroscopy of two fullerenes layered with SnO2. The advantages of a C60 pyrrolidine tris-acid (CPTA) over [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) were demonstrated using their high performance in terms of the number of accumulated charges, location of charge accumulation, and comparison of the charge trap depth. In terms of the number of accumulated charges, a decrease in electrons on CPTA and an increase in the electrons on PC61BM were directly observed in their layered films with SnO2 under light irradiation, which indicates that the CPTA can be sufficient to transfer photocarriers under light irradiation, while PC61BM remains saturated during the transfer of photocarriers leading to the accumulation of charges. In terms of the location of charge accumulation, the electrons on CPTA are accumulated at bulk areas, whereas those on PC61BM are accumulated at the interface between PC61BM and SnO2. The interfacial charge accumulation will demonstrate a negative effect on the device’s performance. In terms of the comparison of the charge trap depth, the number of accumulated electrons on CPTA decreased rapidly, whereas those on PC61BM showed almost no change under dark conditions after light irradiation, indicating that the electrons on CPTA were trapped at a shallower depth than those on PC61BM. The direct observation of charge accumulation states on fullerenes of the fullerene-passivated SnO2 ETLs under light irradiation over time will be essential for optimizing the cell structures and enhancing cell power conversion efficiency and stability.

Solvent-Free Transfer of Freestanding Large-Area Conjugated Polymer Films for Optoelectronic Applications.

Conventional processes for depositing thin films of conjugated polymers are restricted to those based on vapor, liquid, and solution-phase precursors. Each of these methods bear some limitations. For example, low-bandgap polymers with alternating donor-acceptor structures cannot be deposited from the vapor phase, and solution-phase deposition is always subject to issues related to the incompatibility of the substrate with the solvent. Here, a technique to enable deposition of large-area, ultra-thin films (≈20 nm or more), which are transferred from the surface of water, is demonstrated. From the water, these pre-solidified films can then be transferred to a desired substrate, circumventing limitations such as solvent orthogonality. The quality of these films is characterized by a variety of imaging and electrochemical measurements. Mechanical toughness is identified as a limiting property of polymer compatibility, along with some strategies to address this limitation. As a demonstration, the films are used as the hole-transport layer in perovskite solar cells, in which their performance is shown to be comparable to controls formed byspin-coating.

Buried Interface Regulation by Bio-Functional Molecules for Efficient and Stable Planar Perovskite Solar Cells.

Among the factors that lead to the reduction of the efficiency of perovskite solar cells (PSCs) the difficulty involved in realizing a high-quality film and the efficient charge transfer that takes place at the interface between electron-transport layer (ETL) and perovskite is worth mentioning. Here, a strategy for planar-type devices by natural bio-functional interfaces that uses a buried electron-transport layer made of cobalamin complexed tin oxide (SnO2 @B12 ) is demonstrated. Having systematically investigated the effects of SnO2 @B12 interfacial layer in perovskite solar cells, it can be concluded that cobalamin can chemically link the SnO2 layer and the perovskite layer, resulting in improved perovskite film quality and interfacial defect passivation. Utilizing SnO2 @B12 improves the efficiency of planar-type PSCs by 20.60 %. Furthermore, after 250 h of exposure to an ambient atmosphere, unsealed PSCs containing SnO2 @B12 degrade by 10 %. This research provides a viable method for developing bio-functional molecules that will increase the effectiveness and durability of planar-perovskite solar cells.