Lead Iodide Perovskite Solar Cells Research Articles

Fabrication of lead iodide perovskite solar cells by incorporating zirconium, indium and zinc metal-organic frameworks

The study aimed to investigate the role of the metal–organic frameworks in the perovskite solution, and their effects on perovskite crystal, absorption, film formation, and device performance. Three supramolecular compounds of Zirconium(IV), Indium(III) and Zinc(II) with proton transfer compound, obtained from 2,6-pyridinedicarboxylic acid and 2,6-pyridinediamine, were synthesized, and characterized and used as additives in perovskite solar cells. The additives with different amounts were added to the CH3NH3PbI3 solutions to control the morphology of the perovskite layer during the film formation process. More importantly, the metal–organic frameworks serving as additives can help to form a better perovskite layer with fewer voids between CH3NH3PbI3 domains during phase transformation. The findings showed that using a 2 wt% of zinc metal–organic framework in the perovskite layer achieved yields results in the performance of perovskite solar cells. As a result, the current density (Jsc) of the new device increased from 7.02 to 9.36 mA/cm2, and the Fill-Factor (FF) of the device improved from 0.42 to 0.62 for 2 wt% of zinc metal–organic framework. Also, the PCE (Efficiency) of perovskite solar cells achieved more than 90% of improvement after adding 2 wt% of zinc metal–organic framework as an additive in HTM-free conditions. FE-SEM and XRD studied the morphology of this new perovskite layer.

Effects of 5-Ammonium Valeric Acid Iodide as Additive on Methyl Ammonium Lead Iodide Perovskite Solar Cells.

During the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has risen rapidly, and it now approaches the record for single crystal silicon solar cells. However, these devices still suffer from a problem of stability. To improve PSC stability, two approaches have been notably developed: the use of additives and/or post-treatments that can strengthen perovskite structures and the use of a nontypical architecture where three mesoporous layers, including a porous carbon backcontact without hole transporting layer, are employed. This paper focuses on 5-ammonium valeric acid iodide (5-AVAI or AVA) as an additive in methylammonium lead iodide (MAPI). By combining scanning electron microscopy (SEM), X-ray diffraction (XRD), time-resolved photoluminescence (TRPL), current–voltage measurements, ideality factor determination, and in-depth electrical impedance spectroscopy (EIS) investigations on various layers stacks structures, we discriminated the effects of a mesoscopic scaffold and an AVA additive. The AVA additive was found to decrease the bulk defects in perovskite (PVK) and boost the PVK resistance to moisture. The triple mesoporous structure was detrimental for the defects, but it improved the stability against humidity. On standard architecture, the PCE is 16.9% with the AVA additive instead of 18.1% for the control. A high stability of TiO2/ZrO2/carbon/perovskite cells was found due to both AVA and the protection by the all-inorganic scaffold. These cells achieved a PCE of 14.4% in the present work.

Unraveling the Impact of Halide Mixing on Crystallization and Phase Evolution in CsPbX3 Perovskite Solar Cells

Summary All-inorganic perovskite solar cells (PSCs) have attracted wide attention for their excellent thermal stability. However, the detailed crystallization process and complicated phase-transition mechanism of the CsPbX3 film with different halide compositions (I, Br, Cl) remain mysterious. In this study, systematic investigations are performed via state-of-art in situ grazing-incidence wide-angle X-ray scattering to understand the role of the halide elements in all-inorganic perovskite crystallization kinetics, phase-transition, and stabilization mechanism as well as how film morphology and grain size are affected. Based on these results, we were able to fabricate high-performance ternary halide (I, Br, Cl) all-inorganic PSCs through a precise compositional engineering. Our results provide guidance for an in-depth understanding of all-inorganic perovskite materials and pave the way to obtain high-performance all-inorganic PSCs.

A review on power conversion efficiency of lead iodide perovskite-based solar cells

In recent years, lead iodide perovskite solar cells (PSCs) have gained the attention of the researchers due to their high potential to surpass the conventional silicon solar cell. Since lead iodide perovskites have exceptionally high light absorbing capacity, they have been the center point of research for perovskite solar cells. In 2009, the first PSC developed has only 3.8% of power conversion efficiency (PCE) and only in a span of a decade, PCE of 25.2% is achieved. Despite their high PCE, they are still not available for commercial purposes because of their limited life. In this article, we discuss the PSC device configurations developed to achieve higher PCE, the structure of PSC devices, and the stability problem associated with the PSCs which restricts its path for commercial use.

Perovskite Solar Cells: Stable under Space Conditions

Metal halide perovskite solar cells (PSCs) are of interest for high altitude and space applications due to their lightweight and versatile form factor. However, their resilience toward the particle spectrum encountered in space is still of concern. For space cells, the effect of these particles is condensed into an equivalent 1 MeV electron fluence. The effect of high doses of 1 MeV e‐beam radiation up to an accumulated fluence to 1016 e− cm−2 on methylammonium lead iodide perovskite thin films and solar cells is probed. By using substrate and encapsulation materials that are stable under the high energy e‐beam radiation, its net effect on the perovskite film and solar cells can be studied. The quartz substrate‐based PSCs are stable under the high doses of 1 MeV e‐beam irradiation. Time‐resolved microwave conductivity analysis on pristine and irradiated films indicates that there is a small reduction in the charge carrier diffusion length upon irradiation. Nevertheless, this diffusion length remains larger than the perovskite film thickness used in the solar cells, even for the highest accumulated fluence of 1016 e− cm−2. This demonstrates that PSCs are promising candidates for space applications.

Impact of strain relaxation on performance of α-formamidinium lead iodide perovskite solar cells.

High-efficiency lead halide perovskite solar cells (PSCs) have been fabricated with α-phase formamidinium lead iodide (FAPbI3) stabilized with multiple cations. The alloyed cations greatly affect the bandgap, carrier dynamics, and stability, as well as lattice strain that creates unwanted carrier trap sites. We substituted cesium (Cs) and methylenediammonium (MDA) cations in FA sites of FAPbI3 and found that 0.03 mol fraction of both MDA and Cs cations lowered lattice strain, which increased carrier lifetime and reduced Urbach energy and defect concentration. The best-performing PSC exhibited power conversion efficiency >25% under 100 milliwatt per square centimeter AM 1.5G illumination (24.4% certified efficiency). Unencapsulated devices maintained >80% of their initial efficiency after 1300 hours in the dark at 85°C.

Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability

High-performance perovskite/perovskite tandem solar cells require high-efficiency and stable low-bandgap perovskite subcells. State-of-the-art low-bandgap mixed tin–lead iodide perovskite solar cells exhibit either a high power-conversion efficiency or improved stability, but not both. Here we report a two-step bilayer interdiffusion growth process to simultaneously meet both requirements for formamidinium-based low-bandgap mixed tin–lead iodide perovskite solar cells. The bilayer interdiffusion growth process allows for the formation of high-quality and large-grained perovskite films with only 10 mol% volatile methylammonium. Additionally, one-dimensional pyrrolidinium perovskite was applied to passivate the perovskite film and improve the junction quality, which resulted in a carrier lifetime of 1.1 μs and an open circuit voltage of 0.865 V for our perovskite film and device with a bandgap of 1.28 eV. Our strategies enabled a power-conversion efficiency of 20.4% for low-bandgap perovskite solar cells under AM 1.5G illumination. More importantly, an encapsulated device can retain 92% of its initial efficiency after 450 h of continuous 1 sun illumination. Low-bandgap tin–lead perovskites are key to all-perovskite tandem solar cells but simultaneous improvement in efficiency and stability has proven challenging. Now, Li et al. fabricate tin–lead perovskite cells with reduced methylammonium content that are 20.4% efficient and stable under illumination for 450 h.

Polysilane-Inserted Methylammonium Lead Iodide Perovskite Solar Cells Doped with Formamidinium and Potassium

Polysilane-inserted CH3NH3PbI3 perovskite photovoltaic devices combined with potassium and formamidinium iodides were fabricated and characterized. Decaphenylcyclopentasilane layers were inserted at the perovskite/hole transport interface and annealed across a temperature range of 180–220 °C. These polysilane-coated cells prevented PbI2 formation, and the conversion efficiencies were improved over extended periods of time.

Study on hysteresis in perovskite solar cells fabricated using different solvents under ambient conditions

We have investigated the dependency of hysteresis in all-ambient-processed perovskite solar cells on the solvent used for the synthesization of perovskite. Methylammonium lead iodide (MAI) perovskite solar cells have been fabricated using the two-step sequential spin coating method. The influences of PbI2 precursor on the cell performance and its hysteresis are investigated using four different solvents of pure dimethylformamide (DMF), pure dimethyl sulfoxide (DMSO) and mixtures of DMF:DMSO with the ratios of (4:1) and (1:4). The results indicate that a small amount of DMSO in DMF leads to produce large grains of perovskite with proper coverages at the interfaces with hole and electron transport layers. The best conversion efficiency of 10.9% was obtained for the cell prepared by the solvent of (4:1) for DMF:DMSO. The best hysteresis was also obtained from the same cell with the hysteresis index of 0.009.

Addressing the Stability of Lead Halide Perovskites

The rapid rise in efficiencies of lead halide perovskite solar cells has hastened the case for commercialization. One of the key barriers, however, is stability of devices. In this issue of Joule, Zhou et al. studied the degradation mechanism of a FA-Cs mixed cation perovskite-based solar cell with experimental and modeling techniques to show that phase separation into FA-rich and Cs-rich compositions account for the observed degradation.

Co-Evaporated p-i-n Perovskite Solar Cells beyond 20% Efficiency: Impact of Substrate Temperature and Hole-Transport Layer.

For methylammonium lead iodide perovskite solar cells prepared by co-evaporation, power conversion efficiencies of over 20% have been already demonstrated, however, so far, only in n-i-p configuration. Currently, the overall major challenges are the complex evaporation characteristics of organic precursors that strongly depend on the underlying charge selective contacts and the insufficient reproducibility of the co-evaporation process. To ensure a reliable co-evaporation process, it is important to identify the impact of different parameters in order to develop a more detailed understanding. In this work, we study the influence of the substrate temperature, underlying hole-transport layer (polymer PTAA versus self-assembling monolayer molecule MeO-2PACz), and perovskite precursor ratio on the morphology, composition, and performance of co-evaporated p-i-n perovskite solar cells. We first analyze the evaporation of pure precursor materials and show that the adhesion of methylammonium iodide (MAI) is significantly reduced with increased substrate temperature, while it remains almost unaffected for lead iodide (PbI2). This substrate temperature-dependent evaporation behavior of MAI is also transferred to the co-evaporation process and can directly influence the perovskite composition. We demonstrate that the optimal substrate temperature window for perovskite deposition is close to room temperature. At high temperature, not enough MAI for precise stoichiometry is incorporated even with very high MAI rates. While, at temperatures below -25 °C, the conversion of MAI with PbI2 is inhibited, and an amorphous yet unreacted film is formed. We observe that perovskite composition and morphology vary widely between the organic hole-transport layers (HTLs) PTAA and MeO-2PACz. For all substrate temperatures, MeO-2PACz enables higher solar cell PCEs than PTAA. Through the combination of vapor-deposited perovskites and a self-assembled monolayer, we achieve a stabilized power conversion efficiency of 20.6%, which is the first reported PCE above 20% for evaporated perovskite solar cells in p-i-n architecture.

Modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as transparent electrodes for ITO-free perovskite solar cells

In this paper, a dimethyl sulfoxide (DMSO) bathed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS, 1:1.25) film served as the transparent conductive layer (TCL) and the undoped PEDOT:PSS (1:6) film was used as the hole transport layer (HTL) of methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs). Optimal performances (i.e. an open circuit voltage of 0.67 V, a short circuit current density of 20.1 mA cm−2, a fill factor of 51.8%, and a power conversion efficiency of 8.96%) of the PSC were achieved by a two-layer TCL and HTL.

Ionic-Defect Distribution Revealed by Improved Evaluation of Deep-Level Transient Spectroscopy on Perovskite Solar Cells

One of the key challenges for future development of efficient and stable metal halide perovskite solar cells is related to the migration of ions in these materials. Mobile ions have been linked to the observation of hysteresis in the current--voltage characteristics, shown to reduce device stability against degradation and act as recombination centers within the band gap of the active layer. In the literature one finds a broad spread of reported ionic defect parameters (e.g. activation energies) for seemingly similar perovskite materials, rendering the identification of the nature of these species difficult. In this work, we performed temperature dependent deep-level transient spectroscopy (DLTS) measurements on methylammonium lead iodide perovskite solar cells and developed a extended regularization algorithm for inverting the Laplace transform. Our results indicate that mobile ions form a distribution of emission rates (i.e. a distribution of diffusion constants) for each observed ionic species, which may be responsible for the differences in the previously reported defect parameters. Importantly, different DLTS modes such as optical and current DLTS yield the same defect distributions. Finally the comparison of our results with conventional boxcar DLTS and impedance spectroscopy (IS) verifies our evaluation algorithm.

Acetamidinium-Substituted Methylammonium Lead Iodide Perovskite Solar Cells with Higher Open-Circuit Voltage and Improved Intrinsic Stability.

We report acetamidinium (AA)-substituted methylammonium (MA) lead iodide perovskite solar cells. AA has a restricted C-N bond rotation because of delocalized π-electron cloud over the N-C-N bond and the presence of an additional N-H···I bond (4H-bond in AA as compared to 3H-bond in MA). These bonding structures strengthen the electrostatic interaction and stabilize the AA cation inside the perovskite matrix. AA, a larger cation, is substitutional only up to 10%. Devices made with 10% AA-substituted films show an average Voc of 1.12 V, higher than the average Voc of 1.04 V in the case of MA lead halide perovskite (MAPbI3). This increase in Voc can be attributed to an increase in carrier lifetime from 20 μs in the case of MAPbI3 to 32 μs for 10% AA-substituted films respectively. Devices with 18.29% champion and 16.3% average efficiency were fabricated for films with 10% AA. Degradation experiments confirm that the material stability also makes devices more stable; under ambient exposure (72 ± 3% RH), devices with 10% AA retain 70% of their initial power conversion efficiencies (PCEs) up to 480 h. Under the same conditions, the PCEs of reference MAPbI3 devices reduced to 43% of their initial value in 480 h.

Over 20% Efficiency in Methylammonium Lead Iodide Perovskite Solar Cells with Enhanced Stability via "in Situ Solidification" of the TiO2 Compact Layer.

In methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs), the device performance is strongly influenced by the TiO2 electron transport layer (ETL). Typically, the ETL needs to simultaneously be thin and pinhole-free to have high transmittance and avoid shunting. In this work, we develop an "in situ solidification" process following spin coating in which the titanium-based precursor (titanium(diisopropoxide) bis(2,4-pentanedionate)) is dried under vacuum to rapidly achieve continuous TiO2 layers. We refer to this as "gas-phase quenching". This results in thin (60 ± 10 nm), uniform, and pinhole-free TiO2 films. The PSCs based on the gas-phase quenched TiO2 exhibits improved power conversion efficiency, with a median value of 18.23% (champion value of 20.43%), compared to 9.03 and 14.09% for the untreated devices. Gas-phase quenching is further shown to be effective in enabling efficient charge transfer at the MAPbI3/TiO2 heterointerface. Furthermore, the stability of the gas-phase quenched devices is enhanced in ambient air as well as under 1 sun illumination. In addition, we achieve 12.1% efficiency in upscaled devices (1.1 cm2 active area).

Lead Sulfide Quantum Dots as a Bifunctional Layer for Efficient and Stable All‐Inorganic Cesium Lead Iodide Perovskite Solar Cells

AbstractAll‐inorganic cesium lead iodide (CsPbI3) perovskite has aroused great attention while their spontaneous phase transition from the active black α‐phase to the undesired yellow δ‐phase at room temperature has restrained their further application. In addition, the widely‐used organic hole‐transporting materials (HTMs), such as 2,2’,7,7’‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9’‐spirobifluorene (Spiro‐OMeTAD), with hygroscopic additives not only accelerate the phase transition but also hamper the commercialization process because of its high price and complicated synthesis procedure. Herein, we employ colloidal lead sulfide quantum dots (PbS QDs) synthesized by a hot‐injection method as both hole‐transporting material (HTM) and water‐repelling barrier for all‐inorganic α‐CsPbI3 perovskite solar cells (PSCs). The CsPbI3 films capped with PbS QDs as HTM demonstrate much improved phase‐stability and can remain the black α‐phase for at least 30 d without any encapsulation in air. The PSCs with PbS QDs as HTM showed high performance with a power conversion efficiency (PCE) of 7.07%. Furthermore, 89% of the original PCE is remained after storage for 504 h without any encapsulation due to strong moisture resistance resulting from hydrophobic ligands of PbS QDs.

Defect-Engineering-Enabled High-Efficiency All-Inorganic Perovskite Solar Cells.

The emergence of cesium lead iodide (CsPbI3 ) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all-inorganic perovskite material, CsPbI3 :Br:InI3 , is prepared by defect engineering of CsPbI3 . This new perovskite retains the same bandgap as CsPbI3 , while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all-inorganic PSCs based on CsPbI3 :Br:InI3 and carbon electrode exhibit PCE and open-circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI3 can survive only a few days in air. The progress reported represents a major leap for all-inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.

Block Iodide, Save Perovskite Modules

Stability of small area perovskite solar cells has been notably improved, but large area modules have not been proven stable. Recently in Joule, E. Bi and coworkers present a highly stable perovskite module that kept 90% of its initial efficiency after 1,000 h operation under illumination. The secret is an iodide diffusion blocking layer (DBL) added at the module interconnection. The DBL with 2D graphitic carbon nitride (g-C3N4) flakes can suppress iodide diffusion at the interconnection and prevent electrode corrosion.

Enhancement of light harvesting efficiency of perovskite solar cells by using one-dimensional photonic crystals.

We present methyl-ammonium lead iodide perovskite solar cells coupled with one-dimensional photonic crystals (PCs) to achieve enhancement in light harvesting and photocurrent efficiencies. The introduction of PCs as a light reflection layer in the solar cells attributes to the increase in light harvesting efficiency and photocurrent density, which can be tuned by controlling the PC parameters such as the number of layers and layer thickness. Another important feature of the design is the introduction of a thin Au/Ag layer on top, which lets through more than 70% sunlight incident on it into the device, protects the hole transporting layer, and also helps in containing the light reflected from the PC layer into the device for further harvesting. The effects of layer thickness of the perovskite, hole transporting, and metallic contact layers on solar absorption enhancement and photocurrent density are also studied to achieve high power conversion efficiencies. We propose the optimum structural parameters of the considered solar cell structures, which provide the required guidance and also give further opportunities in the design of organo-metal halide perovskite solar cells coupled with PC structures.

Multifaceted Role of a Dibutylhydroxytoluene Processing Additive in Enhancing the Efficiency and Stability of Planar Perovskite Solar Cells.

Significant research efforts are currently being devoted to improving both the crystalline quality and stability of lead halide perovskite absorbers to advance the commercial prospects of perovskite-based solar cells. Herein, we report a simple one-step dibutylhydroxytoluene (BHT) additive-based approach for simultaneously improving the crystallinity and resistance of perovskite films under adverse degradation conditions. We found that BHT, commonly known for its antioxidant properties, can considerably improve the performance of methylammonium lead iodide perovskite solar cells by modulating the chemical environment within the precursor medium to form intermediate complexes, and it can also suppress photooxidation, which results in perovskite degradation under environmental operating conditions. Consequently, a device exhibited a significant power conversion efficiency improvement to 18.1% with the BHT-additive-based perovskite absorber, exceeding the 17.1% efficiency achieved for the control device. The BHT additive also improved the perovskite stability by quenching intermediate reactions resulting in perovskite degradation to an undesirable lead iodide phase, as evidenced by detailed analysis of absorption spectra, grazing-incidence wide-angle X-ray scattering, X-ray photoelectron spectra, and photoluminescence measurements.