CH3NH3PbI3 Films Research Articles

Enhancement the performance of MAPbI3 perovskite solar cells via germanium sulfide doping

In this study, we successfully doped Germanium sulfide (GeS) particles in methylammonium lead triiodide (CH3NH3PbI3) films to create highly efficient inverted perovskite solar cells (PSC). Various characterization methodologies were employed to examine the impact of GeS on the morphological, structural, and compositional properties of the CH3NH3PbI3 perovskite. The X-ray diffraction and Raman spectroscopy analyses of the synthesized products demonstrated that the crystallinity was enhanced, and tetragonal perovskite structures were generated without any impurities when GeS was used at a high concentration. The surface morphology results indicated that the CH3NH3PbI3 perovskite possessed thin coatings with compact, uniform, and smooth surfaces, with large grain size. The production of a high-quality CH3NH3PbI3 film from the CH3NH3PbI3: GeS phase results in improved carrier lifetime, decreased charge-trap density, and nonradiative recombination of the perovskite films. Band gap was observed to be correlated with grain size and crystallinity, which was accompanied by an increase in GeS concentration. We attained a maximum conversion efficiency of 17.46 % by fabricating solar cells with the following structure: soda-lime glass FTO/TiO2/CH3NH3PbI3: GeS/spiro-oMeTAD/Au. Based on our findings, we believe that the doping of GeS is a promising method for improving the properties of perovskite solar cells that are based on CH3NH3PbI3 thin films.

Wide-Range and Multistate Work Functions of Organometallic Halide Perovskite Films Regulated by Ferroelectric Substrates.

Work function of organometallic halide perovskite (OHP) films is one of the most crucial photoelectric properties, which dominates the carrier dynamics in OHP-based devices. Despite surface treatments by additives being widely used to promote crystallization and passivate defects in OHP films, these chemical strategies for modulation of work functions face two trade-offs: homogeneity on the surface versus along the thickness; the range versus the accuracy of modulation. Herein, by using ferroelectric substrates of uniform polarization and subnanometer roughness, homogeneous CH3NH3PbI3 films are fabricated with five states of work functions with large spanning (∼0.8 eV) and high precision (sd ∼ 0.01 eV). We reveal that the ferroelectric polarizations and the smooth surfaces regulate CH3NH3+ orientations and suppress distortions of PbI6 octahedrons. The wide-range and multistate work functions originate from the ordered CH3NH3+ orientations and PbI6 octahedrons, which result in intensity enhancements and wavelength shifts in photoluminescence with a 30-fold increase of photoexcited carrier lifetime.

Electric Field Effects in Hybrid Perovskites Studied via Picosecond Kerr Microscopy.

We present time-resolved Kerr rotation (TRKR) spectra in thin films of CH3NH3PbI3 (MAPI) hybrid perovskite using a unique picosecond microscopy technique at 4 K having a spatial resolution of 2 μm and temporal resolution of 1 ps, subjected to both an in-plane applied magnetic field up to 700 mT and an electric field up to 104 V/cm. We demonstrate that the obtained TRKR dynamics and spectra are substantially inhomogeneous across the MAPI films with prominent resonances at the exciton energy and interband transition of this compound. From the obtained quantum beating response as a function of magnetic field in the Voigt configuration, we also extract the inhomogeneity of the electron and hole Lande g-values and spin coherence time, T2*. We also report the TRKR dependence on both the applied magnetic field and electric field. From the change in the quantum beating dynamics, we found that T2* substantially decreases upon the application of an electric field. At the same time, from the induced spatial TRKR changes, we show that the electric field induced effects are caused by ion migration in the MAPI films.

Exploring the impact of antimony trisulfide (Sb2S3) doping on the optoelectronic functionality of hybrid CH3NH3PbI3 perovskite layers and solar cells

In this study, we present the effect of doping with antimony trisulfide (Sb2S3) nanobare on the electrical, optical, structural, and morpholigcal properties of CH3NH3 PbI3 perovskite thin films. Doped with Sb2S3 nanobare, the thin coatings demonstrated an exceptionally high degree of purity, featuring a tetragonal phase within its single-phase structure. This allowed for the creation of (110) textured CH3NH3PbI3 films, which comprised micrometer-sized grains arranged in a vertical direction across the entire film thickness and featured high crystallinity. Additionally, the CH3NH3PbI3 perovskites films exhibited significant optical absorption at appropriate energy levels and exhibited a high gachin rate of photons. Substance doping methods that can optimize the morphology of the perovskite active layer with large granules are exceedingly desirable in order to reduce charge carrier recombination. The synthesis of perovskite films with dimensions on the order of microns can be achieved by incorporating a regulated quantity of Sb2S3 nanobare into the precursor solution. The incorporation of these textured CH3NH3PbI3:Sb2S3 nanobare films significantly enhanced the power conversion efficiency (PCE) of the perovskite solar cells. The solar cell device configuration utilized in this investigation is as follows: glass/FTO/TiO2/CH3NH3PbI3:Sb2S3 nanobars/spiro-OMeTAD/Au. By employing Sb2S3 nanobars at a concentration of 9 mg/mL, we successfully attained an exceptional power conversion efficiency of 15.87 %. The resulting values for these parameters include an open-circuit voltage VOC of 1.09 V, a short-circuit current density JSC of 21.15 mA/cm2, and a fill factor FF of 68.87 %.

Cryogenic Electron-Beam Writing for Perovskite Metasurface.

Halide perovskites (HPs) metasurfaces have recently attracted significant interest due to their potential to not only further enhance device performance but also reveal the unprecedented functionalities and novel photophysical properties of HPs. However, nanopatterning on HPs is critically challenging as they are readily destructed by the organic solvents in the standard lithographic processes. Here, we present a novel, subtle, and fully nondestructive HPs metasurface fabrication strategy based on cryogenic electron-beam writing. This technique allows for high-precision patterning and in situ imaging of HPs with excellent compatibility. As a proof-of-concept, broadband absorption enhanced metasurfaces were realized by patterning nanopillar arrays on CH3NH3PbI3 film, which results in photodetectors with approximately 14-times improvement on responsivity and excellent stability. Our findings highlight the great feasibility of cryogenic electron-beam writing for producing perovskite metasurface and unlocking the unprecedented photoelectronic properties of HPs.

Boosting optoelectronic performance of (FA)X(MA)1-XPbI3 perovskite solar cells: Via FAI post-treatment engineering

Complex composition engineering of mixed-cations perovskite (FAxMA1-xPbI3) has recently supported rapid progress in perovskite solar cells (PSCs). Nevertheless, it is insufficient to embed and accommodate formamidinium (FA) cation into the MAPbI3 lattice structure via existing methods, leaving behind masses of FA or lead halide content and deteriorating photovoltaic performance. Herein, we present facile surface engineering via post-treated methodology, the surface of CH3NH3PbI3 (MAPbI3) films post-treated with formamidinium iodide (FAI) solution and that results get mixed-cation FAxMA1-xPbI3 perovskite films. The mixed-cation-based FAXMA1-XPbI3 perovskite with significant and large grain size, uniform and compact morphology, highly crystallization, and consequently reducing defect density of the perovskite films can be produced via the present method. It is observed that the film, post-treated with FAI-2, shows results in a very stable and highly crystalline lattice structure with attributes such as extended carrier lifetime, better electron transport, and decreased defect density. The optimized device demonstrates a promising power conversion efficiency (PCE) of 21.89%, and higher than that of the non-treated (19.08%) devices. Furthermore, the devices based on the novel FAI-post-treatment engineering exhibit significantly enhanced stability compared to non-treated devices. Therefore, this approach provides a novel methodology that offers a simple method for producing superior mixed perovskite films, potentially paving the way for the future exploitation of the boosted performance of perovskite solar cells.

Improvement of Perovskite CH3NH3PbI3 Films on Crystallization for Efficient Perovskite Solar Cells with Low-Temperature Anti-solvent Approach

Improvement of Perovskite CH3NH3PbI3 Films on Crystallization for Efficient Perovskite Solar Cells with Low-Temperature Anti-solvent Approach

Accelerated Multisolvent Prediction for Aqueous Stable Halide Perovskite Materials.

Solvent treatment is critical to improving the stability of halide perovskite materials that suffer from notorious issues that inhibit their industrial deployment; however, the complicated perovskite virtual design space with different types of solvent modifiers is inaccessible to traditional trial-and-error methods. In this study, machine learning is employed to predict stable multiple solvent-modified perovskite films under hostile conditions, and a complicated quinary solvent system "DMSO + DMF + toluene + NMP + GBL" is effectively identified to significantly improve the optoelectronic stability of CH3NH3PbI3 in water. The "combinatorial solvent design" approach is realized by an extra tree machine learning model, which leads to a prediction dataset containing aqueous stability labels of 6720 new quinary solvent/perovskite systems. Importantly, the accuracy of the machine learning model is verified via photoelectrochemical experiments, achieving an experimental accuracy of 80%. A machine learning-predicted quinary solvent system offers significantly enhanced aqueous stability and 1000 times larger aqueous photocurrents, compared with the control CH3NH3PbI3 film under the same hostile conditions. This study demonstrates the efficacy of machine learning for solvent design toward stable halide perovskite materials under hostile conditions.

Response of CH3NH3PbI3 films to thermal exposure and proton irradiation

For the purpose of the space application, the thermal stability and proton irradiation effects of the methylammonium lead iodide (MAPbI3, MA+ = CH3NH3+) films have been investigated via the experimental and molecular dynamics (MD) simulation methods. Surface decomposition of MAPbI3 is found to occur at 100 °C, which leads to the formation of a PbI2 layer on the sample surface that suppresses the decomposition of the underlying MAPbI3. PbI2 can be further decomposed into Pb and I2 at 150 °C, creating a porous structure of the film. After 100 keV proton irradiation, the photoluminescence yield from the MAPbI3 keeps almost unchanged with proton fluences up to 1 × 1013 p/cm2, followed by a rapid decrease at the higher fluences. The proton irradiation-induced damage evolution in MAPbI3 is dominated by a pronounced defect recovery, which is owing to the fast migration of the defects in MAPbI3. However, the defect recovery efficiency decreases with increasing defect concentration. The MA component in MAPbI3 is preferentially destroyed by proton irradiation, which accounts for the optical degradation of the film. The reported results provide atomic-level insights into the thermal decomposition processes and the proton irradiation-induced damage accumulation in MAPbI3.

Self‐Powered Perovskite Photodetector Arrays with Asymmetric Contacts for Imaging Applications

AbstractDesigning photodetectors (PDs) with fast response and low power consumption is important for the realization of photoelectric conversion in photoelectric integrated systems. The emerging metal halide perovskite is proven to be a promising material for PD array devices due to its excellent photoelectric performance and large‐area production. However, the array integration of self‐powered perovskite PDs still faces challenges due to the incompatibility between perovskite and micro‐nano processing, hindering practical applications. Here, a perovskite‐compatible device fabrication process is reported for the construction of a perovskite PD array (10 × 10 pixels) with asymmetric contacts, enabling self‐powered photodetection and high‐performance imaging applications. Au and ITO/ZnO electrodes are deposited on the substrate in sequence as the asymmetric contacts. Patterned CH3NH3PbI3 films with uniform and pinhole‐free morphology are then synthesized by a photolithography‐assisted vapor–solution fabrication method as the photosensitive material. The introduction of asymmetric electrodes enables the easy collection of holes at the Au electrode side and electrons at the ITO/ZnO electrode side with light irradiation, resulting in self‐powered photodetection performance. Moreover, the PD array exhibits a uniform distribution of light response and is successfully demonstrated for light imaging. This work opens up a new avenue to develop large‐scale high‐performance perovskite optoelectronic devices with low power consumption.

Characterization of perovskite films prepared with different PbI2 deposition rates

The perovskite (CH3NH3PbI3) films prepared using PbI2 film deposited at controlled deposition rates were evaluated. In this process, PbI2 films were deposited by vacuum evaporation process and then converted into CH3NH3PbI3 films by annealing in methylammonium iodide vapor. The grain size of CH3NH3PbI3 films were successfully tuned from 90 to 125 nm by controlling the PbI2 deposition rate from 0.025 to 0.4 nm s−1. Furthermore, by using the controlled CH3NH3PbI3 film as the light harvesting layer, inverted planar perovskite solar cells were fabricated, and the improvement in power conversion efficiency was confirmed.

Polyacrylonitrile Passivation for Enhancing the Optoelectronic Switching Performance of Halide Perovskite Memristor for Image Boolean Logic Applications.

For the CH3NH3PbI3-based optoelectronic memristor, the high ion-migration randomness induces high fluctuation in the resistive switching (RS) parameters. Grain boundaries (GBs) are well known as the ion-migration sites due to their low energy barrier. Herein, a polyacrylonitrile (PAN) passivation method is developed to reduce GBs of the CH3NH3PbI3 film and improve the switching uniformity of the memristor. The crystal grain size of CH3NH3PbI3 increases with the addition of PAN, and the corresponding number of GBs is consequently reduced. The fluctuations of the RS parameters of the memristor device are significantly reduced. With the memristor, nonvolatile image sensing, image memory, and image Boolean operations are demonstrated. This work proposes a strategy for developing high-performance CH3NH3PbI3 optoelectronic memristors.

CH3NH3PbI3 and CH3NH3PbBr3 films deposited by automated spray-pyrolysis for applications in photovoltaic energy

CH3NH3PbI3 and CH3NH3PbBr3 films deposited by automated spray-pyrolysis for applications in photovoltaic energy

Resolving the Contradiction between Efficiency and Transparency of Semitransparent Perovskite Solar Cells by Optimizing Dielectric‐Metal‐Dielectric Transparent Top Electrode

Semitransparent perovskite solar cells (ST‐PSCs) have recently shown their significance in building‐integrating photovoltaics. Normally, the conductivity and transparency of the top electrode directly affects the properties of the ST‐PSC. The transparency of metal electrodes is extremely sensitive to thickness, but an ultrathin metal film (<10 nm) shows an unexpectedly low conductivity. Herein, a sandwich‐type transparent conductive electrode is designed by combining atomic layer deposition ZnO and thermally evaporated Ag films, and proved that its film conductivity and optical transmittance are superior to metal electrodes with the same thickness. By using an optimized solution‐based thin and continuous CH3NH3PbI3 (MAPbI3) film as the light absorber layer, the ST‐PSCs demonstrate a power conversion effiency of 10% and an average visible transmittance of 19.6%. The results illustrate a strategy of novel structure designs for the electrode to overcome the contradiction between the efficiency and transparency of ST‐PSCs.

Optimizing Photoelectrochemical Photovoltage and Stability of Molecular Interlayer-Modified Halide Perovskite in Water: Insights from Interpretable Machine Learning and Symbolic Regression

Interpretable machine learning models are desired for materials and chemical design processes, while the stable optoelectronic properties of the halide perovskite materials in hostile conditions such as in water are prerequisites for their wider industrial deployment. In this study, we demonstrate an experimentally verified interpretable machine learning pipeline coupled with a symbolic regression method to optimize and understand the stability and photovoltage of the molecular interfacial layer-modified perovskite film in aqueous solution. An accurate machine learning model is achieved via the random forest algorithm; this leads to the successful experimental validation of a champion CH3NH3PbI3/bimolecule/TiO2 system giving a stable photovoltage output in water with two interlayer molecules, basic violet 7 and rhodamine B. The experimental stability and photovoltage outputs of the machine learning-predicted sample in the aqueous solution are enhanced by 4 and 16.7% compared with those of the untreated CH3NH3PbI3 film under the same aqueous conditions; the atomic adsorption structures are then investigated via density functional theory calculations. A t-SR symbolic regression method is developed to design relevant molecular descriptors, which employs a traversal algorithm comparing 8.95 million expressions and obtains a descriptor with 18% improvement. The present study provides a machine learning platform to accelerate the design of stable and high-performance perovskite films in extreme conditions, and the method can be elaborated to other surface systems.

Optical and structural engineering of CH3NH3PbI3 film via CB-antisolvent for efficient and stable perovskite solar cells

Optical and structural engineering of CH3NH3PbI3 film via CB-antisolvent for efficient and stable perovskite solar cells

Grain Boundary Engineering with Cl-Terminated Ti2C Quantum Dots for Enhancing Perovskite Solar Cell Performance

The power conversion efficiency and stability of polycrystalline perovskite solar cells are compromised by grain-boundary-dominated ion migration. Herein, the grain boundaries of CH3NH3PbI3 films were engineered using Ti2C quantum dots. Ti2C quantum dots had a strong interaction with Pb2+ and I– ions, which retarded crystal growth, resulting in larger grain size and less grain boundary in perovskite films. Additionally, the Ti2C quantum dots at the grain boundary could anchor ions and passivate defects, increasing activation energy for ion hopping and reducing trap density. In consequence, perovskite films were used to fabricate solar cells with significantly improved efficiency and stability. These findings may allow the development of versatile grain boundary modifiers for perovskite optoelectronic devices that combine stability and efficiency.

Perovskite solar cells using NaF additive with enhanced stability under air environment

In this study, we report a facile method to enhance the photovoltaic performance of solar cells based on carbon-counter-electrode by introducing NaF additives into the CH3NH3PbI3 (MAPbI3) film. The NaF additives can not only promote the crystallization of perovskite polycrystals but also help to form uniform, high-coverage, and high-quality perovskite films, leading to better light absorption and hydrophobicity. The device with addition of NaF has a maximum power conversion efficiency (PCE) of 11.26%, which is significantly higher than those without NaF (7.66%). Furthermore, the devices with the NaF additive exhibit superior stability, as they retained more than 95% of the original PCE after 2400 h in a humid atmosphere, which is considered to be associated with the presence of NaF and carbon electrode.

Deciphering the role of antisolvent on the structural and optical properties of CH3NH3PbI3 film and its impacts on the performance and stability of n-i-p perovskite solar cells

This study presents an in-depth morphological, structural, and optical study of CH3NH3PbI3 (MAPbI3) film during the antisolvent dripping time, and their relevance to the stability and performance of perovskite solar cells (PSCs) is revealed. The detrimental role of the antisolvent is best demonstrated by using chlorobenzene (CB) as an antisolvent and comparing PSC devices fabricated from CB-free versus PSCs containing CB at different dripping times (5, 10, 15, 20, and 25 s) before the end of deposition of CH3NH3PbI3 film (deposition time was 30 s). Scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis absorption spectroscopy, Urbach energy analysis, steady-state photoluminescence (PL) spectra, current-voltage (I–V), external quantum efficiency (EQE), and water droplet contact angle measurement techniques were utilized to evaluate the characteristics of obtained MAPbI3 films, photovoltaic parameters, and the stability of constructed n-i-p PSCs. It was observed that changing the antisolvent dripping time changes the optical and structural properties of the MAPbI3 layer, including the direct and indirect optical band gap, refractive index, extinction coefficient, dielectric constant, optical conductivity, Urbach energy, dislocation density, lattice strain, crystallite size, and lattice parameters. The above-mentioned parameters were investigated in detail. Accordingly, by dripping the CB at 20 s before the end of the deposition process (labeled as a sample of 20 s), the created MAPbI3 layer had a smoother and pinhole-free surface, resulting in higher crystallinity than the other samples. The values of the direct band gap of the created MAPbI3 films varied from 1.51 to 1.61 eV, corresponding to samples CB-free and 20 s, respectively. For all samples, the indirect band gap was 60 meV lower than the direct band gap. Also, the sample at 20 s had a lower Urbach energy, indicating that this sample's interband defects are less than other models. In addition, the PSCs with CB-dripping at 20 s exhibited higher power conversion efficiency (13.95%) and outstanding stability of power output (<16% decay) as compared to the device without CB-dripping (>82% decay) after keeping in ambient air for about 1450 h at 40 ± 10% RH and 25 ± 5 °C. This systematic comparative study of the structural and optical properties of the perovskite layer can provide a promising platform for achieving high-quality perovskite films to overcome the shortcomings of instability and degradation.

Singular Time‐Dependent Photoconductivity Response of MAPbI3 Samples Deposited by Vacuum Processing on Different Substrates

Organo–inorganic halide perovskites continue to generate enormous interest for their potential use in various optoelectronic devices. Among the different fabrication methods, vacuum thermal deposition allows uniform films over large areas, providing good material quality without using organic solvents. However, the influence of the substrate on the properties of the material deposited by vacuum processing is a point that deserves further investigation. Herein, time‐dependent photoconductivity measurements are used to investigate the dynamics of charge carriers under illumination in planar films of CH3NH3PbI3. The samples are deposited by thermal sublimation on different substrates: PbI2, TaTm, C60, and glass. Experimentally, it is shown that the substrate has a profound effect on perovskite behavior and that photoconductivity is sensitive enough to probe these behaviors. Furthermore, a model based on Shockley–Read–Hall statistics is proposed, explaining the different photoconductivity responses by changing only the relative values of the different capture coefficients and the position of the Fermi level. It is argued that the substrate changes the stoichiometry of the evaporated material, affecting the transient photoconductivity response.