Iodide Precursor Research Articles

Enhanced stability and solar cell performance via π-conjugated Lewis base passivation of organic inorganic lead halide perovskites

Abstract High power conversion efficiency (PCE) and good long-term stability of the perovskite solar cell (PSC) are two important factors on its commercial applications. Here, we propose a simple way to improve the PSC performance by adding 3,3′,5,5′-azobenzene-tetracarboxylic acid (H4abtc) into the lead iodide (PbI2) precursor solution with Lewis acid-base adduct via two-step solution method. 24% enhancement of the PCE is achieved for the PSC with 2.0% H4abtc comparing with the pure PSC without H4abtc. Further research suggests that the H4abtc can passivate grain boundaries of perovskite film by reacting with the lead cation, therefore leading to good thermal stability and anti-moisture of perovskite films. The paper provides a new method to prepare a stable and efficient PSC by employing a novel Lewis base to passivate grain boundaries and gain high-quality perovskite films.

Phenyl-C61-Butyric Acid Methyl Ester Hybrid Solution for Efficient CH3NH3PbI3 Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) have excellent chemical, electronic, and optical properties, making them attractive next-generation thin-film solar cells. Typical PSCs were fabricated with a perovskite absorber layer between the TiO2 electron-transport layer (ETL) and the 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) hole-transport layer (HTL). We examined the influence of phenyl-C61-butyric acid methyl ester (PCBM) on the PSC device. PSCs using the PCBM layer as an ETL were investigated, and the absorber layer was coated by dissolving PCBM in a methyl ammonium lead iodide (MAPbI3) precursor solution to examine the changes at the perovskite interface and inside the perovskite absorber layer. The PSCs fabricated by adding a small amount of PCBM to the MAPbI3 solution exhibited a significantly higher maximum efficiency of 16.55% than conventional PSCs (14.34%). Fabricating the PCBM ETL and PCBM-MAPbI3 hybrid solid is expected to be an efficient route for improving the photovoltaic performance.

Tunable thiocyanate-doped perovskite microstructure via water-ethanol additives for stable solar cells at ambient conditions

Organic-inorganic halide perovskite materials have emerged as highly efficient solar absorbers produced under low-cost processing conditions. However, due to the hygroscopic nature of halide perovskite materials, moisture significantly affects the stability, lifetime and performance of the device. In this work, we combine thiocyanate-doped pseudohalide perovskite with additive solvents to achieve compact films showing high-quality crystal grains with improved longevity of the perovskite films using a simple two-step spin-coating method under ambient conditions. Indeed, we confirm that humidity has a profound impact on the crystal quality. Perovskite films with grain sizes as large as 4 μm are produced in high humidity conditions, using methylammonium iodide precursor solution mixed with deionized water and ethanol. Power conversion efficiencies up-to 9.4% have been achieved for optimized planar device architectures fabricated above 60% relative humidity. Scanning electron microscopy, X-ray diffraction and current-voltage characteristics for devices stored in ambient conditions for more than 480 h show that the films are quite stable with only a 12% decay of their initial power conversion efficiency.

Improving the quality of perovskite based on lead acetate for efficient solar cell

Abstract Organometallic halide perovskite films based on lead iodide precursor often suffered from bad repeatability and the usage of large quantities of toxic solvents due to the need for an anti-solvent washing process. Lead acetate (Pb(Ac) 2 ) precursor, by contrast, was more promising because of the needless of anti-solvent washing during the fabrication of perovskite films. However, the performance of perovskite solar cells (PSCs) needs to be improved. Here, we developed a simple strategy to improve the efficiency of PSCs by adding a small amount of dimethylsulfoxide (DMSO) into the precursor solution of perovskite. An increase in power conversion efficiency (PCE) of PSCs from 13.34% to 15.74% was achieved. It was found that with the addition of DMSO, a stable mesophase structure was formed, which significantly delayed the crystallization of perovskite during the spin-coating of precursor solution, resulting in more uniform and dense perovskite films. The trap intensity and charge carrier mobility of the perovskite films were estimated. The charge carrier dynamic and the recombination in the PSCs were studied. Our method provided a convenient way to improve the performance of PSCs based on Pb(Ac) 2 precursor.

Improved perovskite solar cell efficiency by tuning the colloidal size and free ion concentration in precursor solution using formic acid additive

Abstract Improving the quality of the perovskite active layer is crucial to obtaining high performance perovskite solar cells (PSCs). In this work, by introducing formic acid into the formamidinium lead iodide (FAPbI3) precursor solution, we managed to achieve reduced colloidal size in the solution, leading to more uniform deposition of FAPbI3 film with lower trap state density and higher carrier mobility. The solar cells based on the FAPbI3 absorber layer modified with formic acid show significantly better photovoltaic performance than that on the reference FAPbI3 film without formic acid. The device performance shows a close correlation with the colloidal size. Within the range studied from 6.7 to 1.0 nm, the smaller the colloidal size is, the higher the solar cell efficiency. More specifically, the cell efficiency is improved from 17.82% for the control cell without formic acid to 19.81% when 0.764 M formic acid was used. Formic acid has also been added into a CH3NH3PbI3 (MAPbI3) precursor solution, which exhibits a similar effect on the resulting MAPbI3 films and solar cells, with efficiency improved from 16.07% to 17.00%.

Enhanced Crystallization and Optimized Morphology of Perovskites Through Doping an Indium‐Based Metal–Organic Assembly: Achieving Significant Solar Cell Efficiency Enhancements

Perovskite crystallization and morphology are two essential factors to the photoelectric performances of perovskite solar cells (PSCs). A 3D metal–organic assembly [In2(phen)3Cl6]·CH3CN·2H2O (In2) is introduced for the first time into lead iodide precursor to modify the quality of a perovskite thin film through a two‐step sequential deposition method. As a result, both the lead iodide and perovskite exhibit improved crystallization and modified morphology. The optimized film presents less trap states and is thus in favor of the charge transfer as well as charge collection. Consequently, open circuit voltage (Voc) and fill factor obviously show enhancements from 0.99 to 1.04 V and from 0.66 to 0.71, respectively, yielding a significant increase in a power conversion efficiency from 15.41% to 17.15%. Meanwhile, the hydrophobic property of In2 can increase the moisture resistance of the perovskite, which offers a simple and effective method to improve the stability of PSCs.

Regio- and Stereoselective Synthesis of Spirooxindoles via Mizoroki–Heck Coupling of Aryl Iodides

A method for highly regio- and stereoselective intramolecular Mizoroki–Heck 5-exo cyclization of aryl iodides to the corresponding spirooxindoles has been developed. Electron-rich and electron-deficient aryl iodide precursors were selectively ring-closed with high stereoselectivity and good yields. The double-bond position in the cyclopentene ring was controlled by careful choice of reaction conditions. These rare spiro compounds were further functionalized to rigidified unnatural amino acid derivatives by a subsequent gas-free Pd(0)-catalyzed alkoxycarbonylation, followed by selective O- and N-deprotections.

Effects of methylammonium acetate on the perovskite film quality for the perovskite solar cell

Abstract An ionic-liquid additive of methylammonium acetate (MAAc) is introduced in the lead iodide (PbI2) precursor solution to enhance the morphology and photovoltaic performances of perovskite film through a two-step spin-coating method. The introduction of MAAc at the first step spin-coating process can produce a mixed perovskite of MAPbI3-x(Ac)x, which is capable of generating uniform perovskite film with enough thickness, large grain size, and suitable optical band gap at the second step spin-coating process as a function of crystal seed, resulting in highly efficient generation and transportation of electron for the perovskite solar cell (PSC). As a result, the PSC with 9% MAAc (molar ratio) yields efficiency of 17.07%, which is higher than that of the PSC without MAAc (14.54%). These effects of MAAc in the PbI2 precursor solution on the morphology and photovoltaic performances of perovskite film highlights the potential application of the methylamine compounds as the additives in the cost-effective PSC.

Molecular Iodine for a General Synthesis of Binary and Ternary Inorganic and Hybrid Organic–Inorganic Iodide Nanocrystals

We report the synthesis of various binary and ternary inorganic and hybrid organic–inorganic iodide nanocrystals (NCs) starting from molecular iodine (I2). The synthesis described herein utilizes a reaction between I2 and oleylamine, which results in oleylammonium iodide, an iodide precursor that can be directly used in the preparation of iodide-based NCs. The generality of the synthesis was demonstrated by synthesizing KI, RbI, CsI, AgI, CsPbI3, FAPbI3, Cs4PbI6, Cs3Bi2I9, FA3Bi2I9, and RbAg4I5 NCs. Furthermore, the syntheses are facile and are carried out in vials heated on a hot plate in air. They exhibit not only narrow size distributions, but also, in the case of lead-based perovskites NCs, 70–80% photoluminescence quantum yields. To further prove the high quality of the CsPbI3 and FAPbI3 perovskite NCs, red and infrared bright light-emitting diodes were fabricated, with external quantum efficiencies (EQEs) exceeding 3%, without following any extensive washing procedures.

Efficient Perovskite Solar Cells Fabricated Through CsCl-Enhanced PbI2 Precursor via Sequential Deposition.

The fabrication of high-quality perovskite film highly relies on chemical composition and the synthesis method of perovskite. So far, sequentially deposited MA0.03 FA0.97 Pb(I0.97 Br0.03 )3 polycrystalline film is adopted to produce high-performance perovskite solar cells with record power conversion efficiency (PCE). Fewer grain boundaries and incorporation of inorganic cation (e.g., cesium) would further increase device performance via sequential deposition. Here, cesium chloride (CsCl) is introduced into lead iodide (PbI2 ) precursor solution that beneficially modulates the property of PbI2 film, leading to larger grains with cesium incorporation in the resulting perovskite film. The enlarged crystal grains originate from a slower nucleation process for CsCl-containing PbI2 film when reacting with formamidine iodide, confirmed by in situ confocal photoluminescence imaging. Photovoltaic devices based on CsCl-containing PbI2 film demonstrate a higher averaging efficiency of 21.3% than 20.3% of the devices without CsCl additives for reverse scan. More importantly, the device stability is improved by CsCl additives that retain over 90% of their initial PCE value after 4000 min tracking at maximum power point under 1-sun illumination. This work paves a way to further improve the photovoltaic performance of mixed-cation-halide perovskite solar cells via a sequential deposition method.

The Performance of CH3NH3PbI3 - Nanoparticles based – Perovskite Solar Cells Fabricated by Facile Powder press Technique

Here, we have introduced a facile solid-state route assisted method to prepare CH3NH3PbI3 perovskite nanoparticles (PNs) and together with a facile - powder press technique, for the deposition of prepared PNs - a solution cum vacuum-free route. The perovskite layer was prepared using different lead iodide (PbI2) precursor molar concentrations (0.5, 1, 1.5, 2 mmol) and the PbI2 concentration was found to have a significant impact on the structural, optical, morphological and electrical properties. The sample prepared using molar ratio PbI2: MAI at 1:3 shows the optimal bandgap value (∼1.51 eV), broader band edge peak at 755 nm and found have good optical property for photovoltaic (PV) applications. The J–V performance of the fabricated perovskite device with FTO/c-TiO2/mp-TiO2/Perovskite/CuI/ Cr/Pt-coated FTO counter electrode has been studied. The device fabricated using the concentration at PbI2:MAI 1:3 achieved a PCE of 3.9% and resulted in better long-term stability with deterioration in η and VOC by 27.87% and 29.23% after 15 days.

Temperature Assisted Nucleation and Growth To Optimize Perovskite Morphology at Liquid Interface: A Study by Electrochemical Impedance Spectroscopy

In this work, methylammonium lead tri-iodide perovskite has been synthesized by spin coating of lead acetate trihydrate and methylammonium iodide precursor on preheated substrate. Significant difference in film morphology has been observed as the temperature was varied from room temperature to 120 °C prior to spin coating. Nucleation and growth mechanism is revisited to find out the optimum substrate temperature for fabricating uniform perovskite films and is attributed to the fast homogeneous nucleation followed by delayed growth process. Electrochemical impedance spectroscopy measurement at the perovskite–liquid electrolyte interface reveals the impact of film morphology on the anomalous diffusion behavior observed at the low frequency regime.

Iodine-Promoted Deoxygenative Iodization/Olefination/Sulfenylation of Ketones with Sulfonyl Hydrazides: Access to β-Iodoalkenyl Sulfides.

A highly regio- and stereoselective synthesis of β-haloalkenyl sulfides using commercially available ketones and sulfonyl hydrazides as starting materials has been developed. This protocol obviates the need for alkynes and traditional sulfenylating agents and therefore opens up a new door to construct β-iodoalkenyl sulfides in a highly simple manner. This study reveals that ketones could be used as vinyl iodide precursors in organic synthesis.

New Strategy for Two‐Step Sequential Deposition: Incorporation of Hydrophilic Fullerene in Second Precursor for High‐Performance p‐i‐n Planar Perovskite Solar Cells

AbstractIn p‐i‐n planar perovskite solar cells (pero‐SCs) based on methylammonium lead iodide (MAPbI3) perovskite, high‐quality MAPbI3 film, perfect interfacial band alignment and efficient charge extracting ability are critical for high photovoltaic performance. In this work, a hydrophilic fullerene derivative [6,6]‐phenyl‐C61‐butyric acid‐(3,4,5‐tris(2‐(2‐(2‐methoxyethoxy)ethoxy)ethoxy)phenyl)methanol ester (PCBB‐OEG) is introduced as additive in the methylammonium iodide precursor solution in the preparation of MAPbI3 perovskite film by two‐step sequential deposition method, and obtained a top‐down gradient distribution with an ultrathin top layer of PCBB‐OEG. Meanwhile, a high‐quality perovskite film with high crystallinity, less trap‐states, and dense‐grained uniform morphology can well grow on both hydrophilic (poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonic acid)) and hydrophobic (polytriarylamine, PTAA) hole transport layers. When the PCBB‐OEG‐containing perovskite film (pero‐0.1) is prepared in a p‐i‐n planar pero‐SC with the configuration of ITO/PTAA/pero‐0.1/[6,6]‐phenyl‐C61‐butyric acid methyl ester/Al, the device delivers a promising power conversion efficiency (PCE) of 20.2% without hysteresis, which is one of the few PCE over 20% for the p‐i‐n planar pero‐SCs. Importantly, the pero‐0.1‐based device shows an excellent stability that can retain 98.4% of its initial PCE after being exposed for 300 h under ambient atmosphere with a high humidity, and the flexible pero‐SCs based on pero‐0.1 also demonstrate a promising PCE of 18.1%.

Atmospheric Processing of Perovskite Solar Cells Using Intense Pulsed Light Sintering

Atmospheric processing of metal–organic halide perovskite materials is highly desirable for large-scale manufacturing of solar cells. Atmospheric deposition and thermal processing of perovskite thin films for photovoltaic applications facilitated via rapid intense pulsed light (IPL) processing have been carried out. The interplay between the deposition chemistry, process, and IPL parameters to produce a functional photoactive thin film is discussed. Further addition of polyvinylpyrrolidone (PVP) as functional surfactant is explored to influence grain growth during the IPL process. Structural analysis by x-ray diffraction revealed formation of mixed-phase perovskite crystals from methylammonium chloride and lead iodide precursors. Ultraviolet–visible (UV–Vis) spectroscopy indicated that the light absorption by the perovskite films lay within a narrow band of the visible spectrum with bandgap of 2.9 eV. Scanning electron microscopy characterization of the surface morphology of the perovskite films revealed that addition of PVP to the ink chemistry assisted the IPL process in forming a fully covered surface with clearly defined grains. Functional devices with perovskite thin film processed by IPL under fully atmospheric conditions were demonstrated.

Polytriazolium poly(ionic liquid) bearing triiodide anions: Synthesis, basic properties and electrochemical behaviors

4-Methyl-1-vinyl-1,2,4-triazolium triiodide ionic liquid and its polymer poly(4-methyl-1-vinyl-1,2,4-triazolium) triiodide were prepared for the first time from their iodide precursors via the reaction of iodide (I−) with elemental iodine (I2). The change from iodide to triiodide (I3−) was found to introduce particular variations in the physical properties of these two compounds, including lower melting point/glass transition temperature and altered solubility. The compounds were characterized by single-crystal X-ray diffraction, elemental analysis, and their electrochemical properties examined in solution and in the solid-state. Compared with their iodide analogues, the triiodide salts exhibited lower electrical impedance and higher current in the cyclic voltammetry. We found that poly(4-methyl-1,2,4-triazolium triiodide) was proven to be a promising solid polymer electrolyte candidate.

Optical response of mixed methylammonium lead iodide and formamidinium tin iodide perovskite thin films

Mixed tin (Sn) and lead (Pb) based perovskite thin films have been prepared by solution processing combining methylammonium lead iodide (MAPbI3) and formamidinium tin iodide (FASnI3) precursors. Optical response in the form of complex dielectric function (ε = ε1 + iε2) spectra and absorption coefficient (α) spectra of (FASnI3)1-x(MAPbI3)x based perovskite films have been extracted over a spectral range 0.74 to 5.89 eV using spectroscopic ellipsometry. Absorption band edge energy changes as a function of composition for films including FASnI3, MAPbI3, and mixed x = 0.20, 0.35, 0.40, and 0.6 (FASnI3)1-x(MAPbI3)x perovskites. (FASnI3)0.60(MAPbI3)0.4 is found to have the minimum absorption band edge energy near ∼1.2 eV.

Perovskite ink with wide processing window for scalable high-efficiency solar cells

Perovskite solar cells have made tremendous progress using laboratory-scale spin-coating methods in the past few years owing to advances in controls of perovskite film deposition. However, devices made via scalable methods are still lagging behind state-of-the-art spin-coated devices because of the complicated nature of perovskite crystallization from a precursor state. Here we demonstrate a chlorine-containing methylammonium lead iodide precursor formulation along with solvent tuning to enable a wide precursor-processing window (up to ∼8 min) and a rapid grain growth rate (as short as ∼1 min). Coupled with antisolvent extraction, this precursor ink delivers high-quality perovskite films with large-scale uniformity. The ink can be used by both spin-coating and blade-coating methods with indistinguishable film morphology and device performance. Using a blade-coated absorber, devices with 0.12-cm2 and 1.2-cm2 areas yield average efficiencies of 18.55% and 17.33%, respectively. We further demonstrate a 12.6-cm2 four-cell module (88% geometric fill factor) with 13.3% stabilized active-area efficiency output. Perovskite-based solar cells are often fabricated by methods that are not industrially scalable. Here, Yang et al. develop an ink formulation which gives similar devices by spin coating, the lab-scale standard, and blade coating, which is a more scalable, industry-relevant deposition method.

Photodegradation and removal of organic dyes using cui nanostructures, green synthesis and characterization

Abstract In this research, watermelon, cherry and carrot juices were utilized not only as green reductant, but also as green capping agent for preparation CuI nanostructures for the first time. Watermelon, cherry and carrot juices were applied as green reductant because of the presence of lycopene, beta-carotene and anthocyanin molecules in their components. Besides watermelon, cherry and carrot juices, Cu(NO 3 ) 2 ·3H 2 O and LiI were utilized as copper and iodide precursors for the preparation of CuI nanostructures via a simple, low cost, fast and efficient precipitation approach at ambient situations. By utilizing various amounts of watermelon, cherry and carrot juices, various morphologies of CuI have been gotten. The as-synthesized nanostructures were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, Energy Dispersive X-ray microanalysis (EDX), Transmission electron microscopy (TEM), and Scanning Electron Microscopy (SEM). The photocatalytic activity of the synthesized nanostructures has been evaluated in the photodegradation activity of methyl orange, eosin, erythrosine and acid red 14.

(Invited) Inverted Planar Heterojunction Perovskite Solar Cells Based on Lead Acetate Precursor with Efficiency Exceeding 18%

Organic-inorganic lead halide perovskites are emerging materials for the next-generation photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)2) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)2 and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole-free perovskite films. We observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density-voltage (J-V) hysteresis under the scanning conditions.