Crystallization Of Perovskite Films Research Articles

Controllable intermediates by molecular self-assembly for optimizing the fabrication of large-grain perovskite films via one-step spin-coating

Abstract In the past two years, the introduction of dimethylsulfoxide (DMSO) has recognized as an effective way to prepare high-quality pervoskite films. During the developed DMSO process, the formation of an intermediate phase has proven to uniform crystal growth rates between CH 3 NH 3 I (MAI) and PbI 2 in common solvents. In this work, controllable intermediates were obtained in dimethylformamide (DMF) by additional solvent of DMSO, which tend to be closely packed by means of intermolecular self-assembly. In addition, the bond strength and chemical composition of intermediate phase were investigated with FTIR and TGA. The use of different ratios of DMSO leads to four different complexes of MAI·PbI 2 ·DMF and MAI·PbI 2 ·(DMSO) y (y = 0.6, 1.5, 1.9), thus dramatically influencing the crystallization of perovskite films. Of these complexes, optimized MAI·PbI 2 ·(DMSO) 1.5 intermediate adduct enables highly dense perovskite thin films with large grain size and enhances efficient perovskite solar cells with high charge carrier lifetime.

Fast and Controllable Crystallization of Perovskite Films by Microwave Irradiation Process.

The crystal growth process significantly influences the properties of organic-inorganic halide perovskite films along with the performance of solar cell devices. In this paper, we adopted the microwave irradiation to treat perovskite films through a one-step deposition method for several minutes at a fixed output power. It is found that the specific microwave irradiation process can evaporate the solvent directly and heat perovskite film quickly. In comparison with the conventional thermal annealing process, a microwave irradiation process assisted fast and controllable crystallization of perovskite films with less energy-loss and time-consumption and therefore resulted in the enhancement in the photovoltaic performance of the corresponding solar cells.

Annealing-free perovskite films by instant crystallization for efficient solar cells

Ethyl acetate (EA) is introduced in a one-step spin-coating method and can induce instant crystallization of perovskite films to create efficient thermal annealing-free perovskite solar cells.

Solvent annealing of PbI2 for the high-quality crystallization of perovskite films for solar cells with efficiencies exceeding 18.

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.

Improved Crystallization of Perovskite Films by Optimized Solvent Annealing for High Efficiency Solar Cell

Organic-inorganic halide perovskite-based thin film solar cells show excellent light-to-power conversion efficiency. The high performance for the devices requires the preparation of well-crystallized perovskite absorbers. In this paper, we used the postannealing process to treat the perovskite films under different solvent vapors and observed that the solvent vapors have a strong effect on the film growth. A model regarding the perovskite film growth was proposed as well. Intensive characterizations including scanning electron microscopy, electrochemical impedance spectroscopy, and admittance spectroscopy allowed us to attribute the improved performance to reduced recombination loss and defect density. Solar cell based on the DMSO-treated films delivered a power conversion efficiency of over 13% with negligible photocurrent hysteresis.

Interfacial Charge Transfer Anisotropy in Polycrystalline Lead Iodide Perovskite Films.

Solar cells based on organic-inorganic lead iodide perovskite (CH3NH3PbI3) exhibit remarkably high power conversion efficiency (PCE). One of the key issues in solution-processed films is that often the polycrystalline domain orientation is not well-defined, which makes it difficult to predict energy alignment and charge transfer efficiency. Here we combine ab initio calculations and photoelectron spectroscopy to unravel the electronic structure and charge redistribution at the interface between different surfaces of CH3NH3PbI3 and typical organic hole acceptor Spiro-OMeTAD and electron acceptor PCBM. We find that both hole and electron interfacial transfer depend strongly on the CH3NH3PbI3 surface orientation: while the (001) and (110) surfaces tend to favor hole injection to Spiro-OMeTAD, the (100) surface facilitates electron transfer to PCBM due to surface delocalized charges and hole/electron accumulation at the CH3NH3PbI3/organic interfaces. Molecular dynamic simulations indicate that this is due to strong orbital interactions under thermal fluctuations at room temperature, suggesting the possibility to further improve charge separation and extraction in perovskite-based solar cells by controlling perovskite film crystallization and surface orientation.

ChemInform Abstract: Preparation of Potassium Tantalate Niobate by Sol-Gel Method.

This paper reports on perovskite potassium tantalate niobate (KTN) powders and thin films that were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC{sub 2}H{sub 5}, Ta(OC{sub 2}H{sub 5}){sub 5}, and Nb(OC{sub 2}H{sub 5}){sub 5} in absolute ethanol. The precursor powders crystallized to pyrochlore at {approx}650{degrees}C, and then to perovskite at {approx}750{degrees}C, depending upon Ta:Nb ratio. H{sub 2}O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at 675{degrees}C.

CHEMISTRY-CRYSTALLIZATION-MICROSTRUCTURE RELATIONS OF SOL-GEL DERIVED LANTHANUM MODIFIED LEAD TITANATE THIN FILMS

Lanthanum modified lead titanate thin films have been obtained by the deposition of sol-gel solutions onto platinized (100) silicon substrates. Crystallization of perovskite films was achieved by thermal treatments at 650°C with slow or rapid heatings. Lead oxide excesses were used in the precursor solutions to counterbalance the lead losses produced during the thermal treatment. Rapid heatings and large excesses of lead produce a preferred orientation of the films. These films have more homogeneous and denser microstructures than slow heated films without lead excess.

Preparation of Potassium Tantalate Niobate by Sol–Gel Method

Perovskite potassium tantalate niobate (KTN) powders and thin films were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC2H5, Ta(OC2H5)5, and Nb(OC2H5)5 in absolute ethanol. The precursor crystallized to pyrochlore at ∼ 650°C, and then to perovskite at ∼ 750°C, depending upon Ta:Nb ratio. H2O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at 675°C.