Stability Of CH3NH3PbI3 Research Articles

Isotopic Exchange Extends Charge Carrier Lifetime in Metal Lead Perovskites by Quantum Dynamics Simulations.

One may expect that isotopic exchange has no influence on charge carrier lifetime and perovskite solar cell performance because isotopic effects do not affect the fundamental electronic structure of materials. Experiments defy this expectation. By performing nonadiabatic (NA) molecular dynamics simulations, we demonstrate that hydrogen and deuterium exchange significantly enhances the excited-state lifetime and stability of CH3NH3PbI3. Replacing lighter hydrogen with heavier deuterium suppresses the collective motions of organic and inorganic components, thus enhancing lattice stiffness and decreasing the NA coupling. Isotopic exchange further reduces NA coupling by localizing electron wave functions for separation of electrons and holes, which beats the extended coherence time, slowing down nonradiative electron-hole recombination from CH3ND3PbI3 to CD3ND3PbI3 with respect to the pristine system. The unchanged fundamental electronic structure together with the prolonged carrier lifetime and enhanced stability rationalize the improvement of the deuterated CH3NH3PbI3 solar cells. Our work provides valuable insights into isotope effects for the design of high-performance perovskite photovoltaic and optoelectronic devices.

Unveiling the guest effect of N-butylammonium iodide towards efficient and stable 2D-3D perovskite solar cells through sequential deposition process

Improving the stability of hybrid organic-inorganic halide perovskite materials is urgent and essential for their applications in optoelectronic devices. Here, we introduce n-butylammonium iodide (BAI) into lead-iodide crystals as guest molecules. As a result of guest effect, only a small amount BA2PbI4 two-dimensional (2D) perovskite (n = 1) is formed in PbI2-BAI films. Most of BAI crystals efficiently cut and squeeze the lattice network of lead iodide. The better orientation of 2D lead iodide crystals is obtained via this guest effect. In the following sequential deposition process, that BAI re-dissolve in MAI isopropanol (IPA) solution leads to a mesoporous structure of PbI2 and introduces a 2D perovskite (n = 2) protect layer in 3D MAPbI3 after annealing. Finally, the morphology, crystallization and stability of CH3NH3PbI3 are simultaneously improved by the insertion of BAI guest molecules. Consequently, CH3NH3PbI3 PSCs with an optimized cutting behavior exhibited a power conversion efficiency of 18% and significantly improved the stability.

Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability.

The chemical stabilities of hybrid perovskite materials demand further improvement toward long-term and large-scale photovoltaic applications. Herein, the enhanced chemical stability of CH3 NH3 PbI3 is reported by doping the divalent anion Se2- in the form of PbSe in precursor solutions to enhance the hydrogen-bonding-like interactions between the organic cations and the inorganic framework. As a result, in 100% humidity at 40 °C, the 10% w/w PbSe-doped CH3 NH3 PbI3 films exhibited >140-fold stability improvement over pristine CH3 NH3 PbI3 films. As the PbSe-doped CH3 NH3 PbI3 films maintained the perovskite structure, a top efficiency of 10.4% with 70% retention after 700 h aging in ambient air is achieved with an unencapsulated 10% w/w PbSe:MAPbI3 -based cell. As a bonus, the incorporated Se2- also effectively suppresses iodine diffusion, leading to enhanced chemical stability of the silver electrodes.

Investigation of Structural and Electronic Properties of CH3NH3PbI3 Stabilized by Varying Concentrations of Poly(Methyl Methacrylate) (PMMA)

Studies have shown that perovskites have a high potential of outdoing silicon based solar cells in terms of solar energy conversion, but their rate of degradation is also high. This study reports on improvement on the stability of CH3NH3PbI3 by passivating it with polymethylmethacrylate (PMMA). Structural and electronic properties of CH3NH3PbI3 stabilized by polymethylmethacrylate (PMMA) were investigated by varying concentrations of PMMA in the polymer solutions. Stability tests were performed over a period of time using modulated surface photovoltage (SPV) spectroscopy, X-ray diffraction (XRD), and photoluminescence (PL) measurements. The XRD patterns confirm the tetragonal structure of the deposited CH3NH3PbI3 for every concentration of PMMA. Furthermore, CH3NH3PbI3 coated with 40 mg/mL of PMMA did not show any impurity phase even after storage in air for 43 days. The Tauc gap (ETauc) determined on the basis of the in-phase SPV spectra was found in the range from 1.585 to 1.62 eV for the samples stored during initial days, but shifted towards lower energies as the storage time increased. This can be proposed to be due to different chemical reactions between CH3NH3PbI3/PMMA interfaces and air. PL intensity increased with increasing concentration of PMMA except for the perovskite coated with 40 mg/mL of PMMA. PL quenching in the perovskite coated with 40 mg/mL of PMMA can be interpreted as fast electron transfer towards the substrate in the sample. This study shows that, with an optimum concentration of PMMA coating on CH3NH3PbI3, the lifetime and hence stability on electrical and structural behavior of CH3NH3PbI3 is improved.

Light-Induced Degradation of CH3NH3PbI3 Hybrid Perovskite Thin Film

The stability of CH3NH3PbI3 was investigated by observing the degradation in a coevaporated film irradiated by a blue laser in ultrahigh vacuum. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were employed to investigate the effects of irradiation on the surface. The core levels of CH3NH3PbI3 were observed to shift toward a higher binding energy (BE) during the irradiation, suggesting that the surface became more n-type. A new metallic Pb component in the XPS spectrum appeared after 120 min of irradiation, indicating that the film had started to decompose. The decomposition saturated after about 480 min of irradiation when the ratio of metallic Pb to total Pb was about 33%. Furthermore, the film was no longer continuous after irradiation, as the elements gold and oxygen from the substrate were detected by XPS. SEM images also show a roughened surface after irradiation. The results strongly indicate that CH3NH3PbI3 is sensitive to the laser irradiation and that the light indu...

Effect of crystal structures on the stability of CH3NH3PbI3 under humidity environment

The efficiency of organic-inorganic hybrid perovskite (CH3NH3PbI3, MAPbI3) solar cells has been dramatically increased from 3.8% to 20.1% in the past five years, which is close to its theoretical limit. Nevertheless, the stability of perovskite solar cells remains a major hurdle for its commercialization. Here, we investigated the morphology and structure of MAPbI3 films with different preparation conditions, and reported the existence of orthorhombic structure in tetragonal MAPbI3 cuboids at room temperature. More interestingly, a special orthorhombic-to-tetragonal phase transition could lead to intensity oscillations in the time evolution of photoluminescence (PL), and increased the films stability in a high humidity (∼50%) environment. Furthermore, we used the films to prepare photovoltaic devices with a half-life over 200h, and showed the potential of the phase transition to improve the lifetime and practical application for perovskite solar cells.

The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

AbstractIn this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite‐based photoactive layers. When exposed to both light and dry air the mp‐Al2O3/CH3NH3PbI3 photoactive layers rapidly decompose yielding methylamine, PbI2, and I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2− species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2− generation is significantly reduced when the mp‐Al2O3 film is replaced with an mp‐TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.