Hybrid Perovskite Thin Films Research Articles

Direct measurement of radiative decay rates in metal halide perovskites

A radiometric measurement of time-resolved photoluminescence that helps to identify unwanted photocarrier decay in hybrid perovskite thin-films for solar cell applications.

The phase-controllable crystallization induced by low pressure flashing in chloride anion doped quasi-2D hybrid perovskite thin films for blue light-emitting diodes

Controlling perovskite phase composition plays an important role in improving the quality of quasi-2D blue emissive perovskite thin films to realize spectrally stability of perovskite LED (PeLED). Herein, the high quality quasi-2D perovskite thin films were prepared by low pressure flashing induce crystallization (LPFC) method, which promoted surface coverage of perovskites to control the removal speed of solvent mixtures unanimously by adjusting the pressure of post-treatment from 1 KPa to 101 KPa. Compared to the common post-treatment method, perovskite thin films produced different quasi-2D phase under the pressure of 20 KPa by LPFC method and corresponding devices possessed high luminance with spectrally stability. Furthermore, the facile LPFC method promoted the volatile speed of high boiling point single solvent and accelerate the crystallization process to realize high quality of quasi-2D perovskite thin films prepared at room temperature.

Correlation of THz-wave absorption properties by different halogen elements in FAPb(Br, I)-based hybrid perovskite thin films

Understanding the controllability of the THz-wave absorption property of organic–inorganic hybrid perovskite (OHP) thin films is necessary to advance the THz-based application field. Here, we found the correlation of THz-wave absorption property by different halogen elements in FAPb(Br, I)-based hybrid perovskite thin films fabricated by sequential vacuum evaporation. We confirm that the selection of halogen elements and their concentration ratio can be changed to systematically control the THz conductivity property.

Terahertz Wave Absorption Property of all Mixed Organic-Inorganic Hybrid Perovskite Thin Film MA(Sn, Pb)(Br, I)3 Fabricated by Sequential Vacuum Evaporation Method.

All mixed hybrid perovskite (MA(Sn, Pb)(Br,I)3) thin film was fabricated by sequential vacuum evaporation method. To optimize the first layer with PbBr2 and SnI2, we performed different annealing treatments. Further, MA(Sn, Pb)(Br, I)3 thin film was synthesized on the optimized first layer by evaporating MAI and post-annealing. The formed hybrid perovskite thin film exhibited absorptions at 1.0 and 1.7 THz with small absorbance (<10%). Moreover, no chemical and structural defect-incorporated absorption was found. In this study, the possibility of changing terahertz absorption frequency through the mixture of metal cations (Sn+ and Pb+) and halogen anions (Br− and I−) was verified.

Alleviating halide perovskite surface defects

Alleviating halide perovskite surface defects

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

Summary Understanding defects is of paramount importance for the development of stable halide perovskite solar cells (PSCs). However, isolating their distinctive effects on device efficiency and stability is currently a challenge. We report that adding the organic molecule 3-phosphonopropionic acid (H3pp) to the halide perovskite results in unchanged overall optoelectronic performance while having a tremendous effect on device stability. We obtained PSCs with ∼21% efficiency that retain ∼100% of the initial efficiency after 1,000 h at the maximum power point under simulated AM1.5G illumination. The strong interaction between the perovskite and the H3pp molecule through two types of hydrogen bonds (H…I and O…H) leads to shallow point defect passivation that has a significant effect on device stability but not on the non-radiative recombination and device efficiency. We expect that our work will have important implications for the current understanding and advancement of operational PSCs.

Hybrid perovskite films deposited by thermal evaporation from a single source

Hybrid perovskites, such as MAPbI3, are very promising materials to fabricate highly efficient and low-cost solar cells and photodetectors. In this work, we propose a new method of deposition of hybrid perovskite thin films through thermal evaporation of MAPbI3 powder from a single source for which was evaluated the effect of evaporation parameters (distance, time, substrate temperature, chamber pressure, and crucible heating rate) on the structural, optical, and morphological properties. It was found that it is necessary to control adequately the chamber partial pressure, substrate temperature, and the crucible heating rate in order to obtain single-phase MAPbI3 perovskite films. Also, it was studied the solvent annealing treatment as a method to increase the grain size of evaporated films. Finally, a study of transient and steady-state photoconductivity allowed verifying that the evaporated MAPbI3 films present fast band to band photogeneration and bimolecular recombination, and also that the grain size growth leads to an increase of the photoconductivity intensity due to the improvement of the diffusion length.

Wide and Tunable Bandgap MAPbBr3−xClx Hybrid Perovskites with Enhanced Phase Stability: In Situ Investigation and Photovoltaic Devices

The current understanding of the crystallization, morphology evolution, and phase stability of wide‐bandgap hybrid perovskite thin films is very limited, as much of the community's focus is on lower bandgap systems. Herein, the crystallization behavior and film formation of a wide and tunable bandgap MAPbBr3−xClx system are investigated, and its formation and phase stability are contrasted to the classical MAPbI3−xBrx case. A multiprobe in situ characterization approach consisting of synchrotron‐based grazing incidence wide‐angle X‐ray scattering and laboratory‐based time‐resolved UV–Vis absorbance measurements is utilized to show that all wide‐bandgap perovskite compositions of MAPbBr3−xClx studied (0 &lt; x &lt; 3) crystallize the same way: the perovskite phase forms directly from the colloidal sol state and forms a solid film in the cubic structure. This results in significantly improved alloying and phase stability of these compounds compared with MAPbI3−xBrx systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI3). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin‐hole‐free MAPbBr3−xClx hybrid perovskite thin films with a tunable bandgap are, thus, integrated into working single‐junction solar cell devices and achieve a tunable open‐circuit voltage as high as 1.6 V.

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Summary The development of mixed tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) with low band gap (1.2–1.4 eV) has become critical not only for pushing single-junction devices toward the maximum efficiency given by the Shockley-Queisser limit, but also for enabling all-perovskite tandem devices beyond this limit. However, achieving high power-conversion efficiency (PCE) and long-term device operation stability simultaneously remains a significant challenge for Sn-Pb-based PSCs. Here, we demonstrate near ideal-band-gap (∼1.34 eV) methylammonium-free Sn-Pb-based PSCs with high efficiency (∼20%) and promising operational stability of maintaining >80% of initial PCE over 750 h under maximum-power-point tracking. The key to this success is the use of a SnCl2⋅3FACl complex additive that improves the microstructure and reduces the development of residual stress in the Sn-Pb perovskite thin films, which in turn enhances the efficiency and stability of the Sn-Pb-based ideal-band-gap PSCs.

Role of Photon Recycling and Band Filling in Halide Perovskite Photoluminescence under Focussed Excitation Conditions

We study the temporal, spatial, and spectral evolution of charge carriers in hybrid perovskite thin films after optical excitation with a small laser spot. These are conditions typical of microscop...

Memory Devices via Unipolar Resistive Switching in Symmetric Organic–Inorganic Perovskite Nanoscale Heterolayers

Organic–inorganic hybrid perovskite thin films with nanostructured polycrystalline grains have shown great potential in various nanoscale optoelectrical applications. Among them, the field of elect...

Pressing challenges of halide perovskite thin film growth

The adoption of new thin-film materials in high-end technologies, such as monolithic tandem solar cells and integrated circuits, demands fabrication processes that allow a high level of control over film properties such as thickness, conformality, composition, and crystal structure. Achieving this with traditional optoelectronic materials, such as silicon, indium phosphide, gallium arsenide, silicon nitride, and several metal oxides, has opened the way for applications such as high-efficiency photovoltaics, light emitting devices, and integrated photonics. More recently, halide perovskites have demonstrated huge potential in optoelectronic applications, showing exceptional photovoltaic properties, light emission, and lasing performance. Common growth techniques for these halide perovskites have been solution-based methods. Optimized solution-based processes yield high quality thin films well-suited for applications, such as single-junction solar cells, but remain incompatible with integration into complex devices such as monolithic tandem photovoltaics and photonic circuits. Therefore, new fabrication methods allowing atomic, structural, and compositional precision with the conformal growth of hybrid and multi-compound halide perovskite thin films are of utmost importance for material exploration and for their application in complex devices. This Perspective reviews the progress on synthesis methods of halide perovskite thin films, discusses pressing challenges, and proposes strategies for growth control, versatile film deposition, monolithic device integration, epitaxial growth, and high-throughput synthesis to discover novel and non-toxic stable metal halide compositions.

In situ NMR Investigation of the Photoresponse of Perovskite Crystal

Summary Hybrid perovskites are outstanding candidates for use in optoelectronic devices. Nonetheless, hybrid perovskites present numerous fundamental issues that are not yet fully understood. This study seeks to address this problem by reporting on the occurrence of ultraslow dynamic orientation changes in the methylammonium (MA) cations and the corresponding changes in the inorganic lattice of MAPbI3 perovskite crystals occurring over a time scale of 100 s under continuous illumination based on in situ single-crystal 2H nuclear magnetic resonance and in situ X-ray diffraction results. The demonstrated ultraslow dynamic changes in MAPbI3 are far slower than elementary molecular motions typically having time scales of femtoseconds and picoseconds and have never been reported previously. The ultraslow dynamic changes have been correlated with the reduction of band gap and the increase of absorption coefficient of MAPbI3, providing the molecular origins of the stabilization process in the photoresponse of the MAPbI3 device.

The King of the New Generation Photovoltaic Technologies——Perovskite Solar Cells & the Opportunities and Challenges

Within the past several decades, photovoltaic technology is an emerging pioneer in the renewable energy field. Driven by the rapid decline in the price of photovoltaic products, the cost of photovoltaic power generation is becoming cheaper or even lower than the cost of thermal power generation. Among various photovoltaic technologies, organic-inorganic hybrid perovskite thin film solar cells are promising candidates for the next generation of solar cells in consideration of their outstanding advantages such as low-cost, easy manufacturing processing and high power conversion efficiencies. Perovskite solar cells stem from dye-sensitized solar cells. Within less than a decade of rigorous research and development in perovskite solar cells, the efficiency is boosted up to 25.2%. Aforementioned high PCE is mainly attributed to outstanding photovoltaic properties such as the long diffusion length of carriers, high optical absorption coefficient, excellent carrier mobility, etc. Meanwhile, the main barriers of commercialization for the perovskite solar cells are the poor stability of the devices, and the possible environmental pollution caused by lead. Herein, we briefly reviewed the opportunities and the challenges of this game changer in photovoltaic field. The development prospective are also discussed.

Unique phonon modes of a CH3NH3PbBr3 hybrid perovskite film without the influence of defect structures: an attempt toward a novel THz-based application

The exploration of new physical properties for various THz-based applications, such as THz-wave sensing, modulation, and imaging devices, is a key challenge in the research on organic–inorganic hybrid perovskite materials. These THz-based applications require satisfactory, sensitive, and stable absorption properties with values between 0.5 and 3 THz. To achieve these properties, candidate materials should possess a purified structure that induces regular and fixed phonon modes without any defects or impurities. CH3NH3PbBr3, an organic–inorganic hybrid perovskite thin film produced by a sequential vacuum evaporation method on a flexible PET substrate, was investigated in this study. Although the thin film contains only molecular defects related to CH3NH2 incorporated into the perovskite structure, our THz-wave absorption measurement and first-principles simulation confirmed that these molecular defects do not influence the three phonon modes originating from the transverse vibration (0.8 THz), the longitudinal optical vibrations (1.4 THz) of the Pb–Br–Pb bonds, and the optical Br vibration (2.0 THz). After spin-casting an ultrathin PTAA polymer protective layer (5 nm) on the hybrid perovskite thin film, it was additionally observed that there was no significant effect on the phonon modes. Thus, this novel flexible organic–inorganic hybrid perovskite material is a potential candidate for THz-based applications.

Growth kinetics of hybrid perovskite thin films on different substrates at elevated temperature and its direct correlation with the microstructure and optical properties

We elucidate the growth kinetics and scaling behavior of vacuum deposited CH3NH3PbBr3 thin film on various substrates and correlate the same with its microstructural and optical properties. Analysis of the AFM images reveals an abrupt change in the grain features for thickness, d ≥ 40 nm. Based on the evaluation of the scaling parameters, the perovskite films exhibit an anomalous scaling behavior for, d < 40 nm, and stable growth for, d ≥ 40 nm. Interestingly, the growth exponent (β) is found to be distinctly different, ~0.22 and ~ 0.90, for the films on ITO and SiO2 substrates, respectively. The study of the temperature-dependent growth kinetics yields higher activation energy (Ea) for SiO2 (~0.15 eV) than that of ITO (~0.10 eV). Due to mound-like growth, the film on SiO2 substrate deviates from the conventional scaling law. Structural and photoluminescence (PL) studies reveal better crystallinity of the film on ITO, which is consistent with its low Ea value. Optical absorbance and PL analyses reveal a blue shift in the bandgap with decreasing thickness attributed to the lattice expansion. These findings provide new insights on the growth kinetics and optimum conditions for the vacuum deposition of hybrid perovskite thin films on various substrates.

Structural Regulation for Highly Efficient and Stable Perovskite Solar Cells via Mixed-Vapor Deposition

Because of a lack of solvent-assisted crystallization, vapor and reaction process controls are essential for structural regulation in vapor-deposited organic–inorganic hybrid perovskite thin films....

Strong Linear Correlation between CH3NH2 Molecular Defect and THz-Wave Absorption in CH3NH3PbI3 Hybrid Perovskite Thin Film.

To control the density of a CH3NH2 molecular defect, which strongly contributed to a significant THz-wave absorption property in the CH3NH3PbI3 hybrid perovskite thin film formed by the sequential vacuum evaporation method, we performed post-annealing processes with various temperatures and times. In the thin film after post-annealing at 110 °C for 45 min, the density of the CH3NH2 molecular defect was minimized, and CH3NH3I and PbI2 disappeared in the thin film after the post-annealing process at 150 °C for 30 min. However, the density of the CH3NH2 molecular defect increased. Moreover, the THz-wave absorption property for each thin film was obtained using a THz time-domain spectroscopy to understand the correlation between the density of a molecular defect and the THz-wave oscillation strength at 1.6 THz, which originated in the molecular defect-incorporated hybrid perovskite structure. There is a strong linear correlation between the oscillator strength of a significant THz-wave absorption at 1.6 THz and the CH3NH2 molecular defect density.

From Metallic Lead Films to Perovskite Solar Cells through Lead Conversion with Polyhalide Solutions.

Solutions of methylammonium and formamidinium polyhalides (AX1+n, A = MA, FA, X = I, Br) in isopropanol are introduced as novel versatile precursors for the fabrication of APbX3 hybrid perovskite thin films via oxidation of metallic Pb. The polyhalide solution with adjustable reactivity is distributed over a metallic Pb layer followed by iodine vapor postprocessing to tune the morphology and composition of the film using only the elements inherently present in the perovskite. This method is easily reproducible in any materials science laboratory with equipment commonly used for perovskite solar cell fabrication and resulted in power conversion efficiencies of 16.2 and 17.2% for planar solar cells using MAPbI3 and MA0.25FA0.75PbI2.75Br0.25 perovskites, respectively, as a proof of concept. Implementation of metallic lead thin films as the single Pb-containing precursors reduces a number of in-lab handling hazards compared to classical PbI2 powder and solutions and provides a variety of scalable deposition options.

Influence of morphology on photoluminescence properties of methylammonium lead tribromide films

The morphology of hybrid perovskite thin films plays a crucial role for their photophysical properties. However, the underlying mechanisms are still unclear. To gain further insight into this phenomenon, methylammonium lead tribromide films of different morphology were investigated using photoluminescence spectroscopy. Photostability measurements demonstrate three mechanisms: (A) reversible degradation of the photoluminescence, depending positively on the grain-boundary density, which is presumably caused by photo-induced bromide vacancies, (B) enhancement of the photoluminescence intensity in the presence of oxygen and moisture and (C) destruction of the perovskite after several minutes of ultraviolet illumination with excitation power above 100 W/cm2. Both the intensity and the lifetime of the photoluminescence were significantly smaller in films with micrometer-sized crystallites compared to granular films. This is ascribed to crystals being partially isolated in the former, causing smaller diffusion lengths, whereas the carriers in the granular films can diffuse from grain to grain resulting in higher photoluminescence lifetime and intensity.