Organic-inorganic Hybrid Perovskite Films Research Articles

High-Quality CH3NH3PbI3 Films Obtained via a Pressure-Assisted Space-Confined Solvent-Engineering Strategy for Ultrasensitive Photodetectors.

High-quality organic-inorganic hybrid perovskite films are crucial for excellent performance of photoelectric devices. Herein, we demonstrate a pressure-assisted space-confined solvent-engineering strategy to grow highly oriented, pinhole-free thin films of CH3NH3PbI3 with large-scale crystalline grains, high smoothness, and crystalline fusion on grain boundaries. These single-crystalline grains vertically span the entire film thickness. Such a film feature dramatically reduces recombination loss and then improves the transport property of charge carriers in the films. Consequently, the photodetector devices, based on the high-quality CH3NH3PbI3 films, exhibit high photocurrent (105 μA under 671 nm laser with a power density of 20.6 mW/cm2 at 10 V), good stability, and, especially, an ultrahigh on/off ratio (Ilight/Idark > 2.2 × 104 under an incident light of 20.6 mW/cm2). These excellent performances indicate that the high-quality films will be potential candidates in other CH3NH3PbI3-based photoelectric devices.

Circularly polarized photoluminescence and Hanle effect measurements of spin relaxation in organic–inorganic hybrid perovskite films

Partial circularly polarized photoluminescence with polarization degree of 2% from CH3NH3PbBr3 film at 77 K is observed, excited using a circularly polarized 532 nm laser. Moreover, the Hanle effect is measured to study spin relaxation in CH3NH3PbBr3 film, yielding a spin lifetime of ∼240 ps at 77 K.

Synergistic effect of anions and cations in additives for highly efficient and stable perovskite solar cells

The use of a synergistic additive NH4SCN in constructing organic–inorganic hybrid perovskite films improves the quality of perovskite films, enhances the stability, and promotes the device efficiency.

The influence of DMSO and ether via fast-dipping treatment for a perovskite solar cell

Preparing dense organic-inorganic hybrid perovskite film is hindered by the extremely low solubility of lead(II) iodide (PbI2) at one-step coating process using one-solution (PbI2 + CH3NH3I + DMF). Thus, dimethyl sulfoxide (DMSO) has been widely used to enhance the solubility through the formation of adducts. However, the required mixture of DMSO and DMF cannot be simultaneously evaporated at low temperatures, owing to the different boiling points, which are influenced by the surface morphology. Consequently, this also affects the solar energy conversion efficiency of the perovskite solar cells. In this study, we develop a new approach for controlling the evaporation of DMF and DMSO by dip-coating ether on the top of the prepared thin film composed of PbI2, methylammonium iodide (MAI), DMF, and DMSO. Interestingly, it reveals that ether acted as an agent for simultaneous evaporation at similar temperatures, which then allows it to control surface morphology, and achieve dense perovskite. The fabricated inverted-perovskite PbI2 thin film solar cell shows that the efficiency reached up to 16.3% with high reproducibility. The ether-dipping post-treatment serves as a promising means for enhancing the efficiency of perovskite solar cells.

Properties of atmospheric‑hydrogen-plasma-treated CH3NH3PbI3 perovskite films

Caused by unique properties of organic-inorganic hybrid perovskite films, the patterning process is very challenging. In this study, novel method for etching of perovskite film is suggested using atmospherically hydrogen-containing plasma treatment. It is illustrated successful eating of methylammonium triiodideplumbate (CH3NH3PbI3) perovskite films on glass substrates. Perovskite layers are processed for various times between 2s and 300s. Based on the transformation of film's morphology upon treatment time three regions are distinguished; i.e. short (less than 10s), medium (up to 180s) and long (>180s). Although onset of the early modifications is observed after 10s treatment the bulk characteristics of the film remain mainly the same. After 30s treatment nano-sized particles are observed in the entire film. When plasma treatment performed longer period i.e. 180 and 300s, some particles are agglomerated forming relatively large clusters. The morphological and chemical properties of the plasma-processed films are analyzed using various analytical tools such as scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy coupled with SEM or TEM (EDS-SEM and EDS-TEM), and x-ray photoelectron spectroscopy (XPS).

Spontaneous Passivation of Hybrid Perovskite by Sodium Ions from Glass Substrates: Mysterious Enhancement of Device Efficiency Revealed

The efficiency of a solar cell generally decreases over time due to degradation of the devices. Here we report a spontaneous increase of device efficiency for organic–inorganic hybrid perovskite (OIHP) solar cells after a period of storage that is speculated to be related to the sodium ions (Na+) diffused from the substrate. The efficiency of a p–i–n planar heterojunction structure device rises from 18.8 to 20.2% after 24 h of storage in nitrogen. The increased efficiency can be explained by the prolonged carrier lifetime and reduced trap density in the OIHP films. The expected contribution by Na+ in defect passivation has been evidenced by studying the evolution of the film’s photoluminescence (PL) lifetime, trap density, and device efficiency over storage duration on varied substrates that either contain Na+ or do not. The passivation effect of Na+ is further identified by the improved PL lifetime observed in the OIHP film made on a silicon substrate with intentionally added Na+.

Synthesizing conditions for organic-inorganic hybrid perovskite using methylammonium lead iodide

We investigate mechanisms for the formation of organic-inorganic hybrid perovskite films based on the mixture of methylammonium lead iodide (CH3NH3PbI3). Using a series of weight-to-weight concentration and composition ratio of the precursor solution, perovskite films were synthesized and characterized, which exhibit different spectroscopic and microscopic properties. Based on the criteria that the synthesized film should have excellent crystallization into perovskite structures, high optical absorption, high film homogeneity and surface smoothness, we were able to resolve an optimized concentration of 45% and an optimized molar ratio of 2:1 for the mixture precursor solution of CH3NH3I and PbI2 in DMF.

Tailoring nucleation and grain growth by changing the precursor phase ratio for efficient organic lead halide perovskite optoelectronic devices

The nucleation and growth of organic–inorganic hybrid perovskite films induced by the molar ratio of precursor components and their role in optoelectronic performance are investigated.

Effects of thermal treatment on organic-inorganic hybrid perovskite films and luminous efficiency of light-emitting diodes

To improve the electroluminescence efficiency of organic-inorganic hybrid perovskite (OIP) films, we need to consider several different types of post-treatments after film formation such as thermal annealing and solvent annealing. Here, we only applied thermal treatment on the film excluding all the other treatments. Then, we analyzed the effects of annealing time tann on crystallinity of methylammonium lead bromide (CH3NH3PbBr3) films and on luminous efficiency of CH3NH3PbBr3-based perovskite light-emitting diodes (PrLEDs). When thermal annealing of CH3NH3PbBr3 films was conducted at 90 °C, tann ≤ 10 min increased its crystallinity by eliminating residual solvent and completing the conversion of precursor to crystal, but tann > 10 min reduced crystallinity and caused slight sublimation of CH3NH3Br. This was consistent with trend of the luminous efficiency of our PrLEDs that showed the optimum performance at tann = 10 min. These results demonstrate that optimizing tann of CH3NH3PbBr3 films is a simple way to improve the luminous efficiency of PrLEDs by controlling their crystallinity.

Solution-induced morphology change of organic-inorganic hybrid perovskite films for high efficiency inverted planar heterojunction solar cells

Planar heterojunction perovskite solar cell promises low cost solution manufactured solar cells with the efficiency of single crystal silicon cells. However, it is still a great challenge to fabricate high quality perovskite films by solution method. Here, we demonstrate a simple method to control the morphology of perovskite film deposited on the top of a PEDOT: PSS coated ITO glass. The key to the process is to induce a change at the stage of the nucleation of intermediate phase, leading to the homogenous high density nucleation of the particles without preferred orientation instead of the sparse nucleation of the needle shaped crystals by a solvent treatment using a solvent which is miscible with the solvent of the perovskite precursor solution, but less soluble to the precursors of PbI2 and CH3NH3I. The morphology of the intermediate phase determines the morphology of final perovskite film. Planar inverted heterojunction perovskite solar cells fabricated using the perovskite films deposited by the method as the absorb layer show a reproducible efficiency of 13.1%.