Two-step Sequential Deposition Process Research Articles

Multifunctional Metal-organic Frameworks Capsules Modulate Reactivity of Lead Iodide toward Efficient Perovskite Solar Cells with Ultraviolet Resistance.

The two-step sequential deposition process is demonstrated as a reliable technology for the fabrication of efficient perovskite solar cells (PVSCs). However, the complete conversion of dense PbI2 to perovskite in planar PVSCs is tough without mesoporous titanium dioxide as support. Herein, multifunctional capsules consisting of zeolitic imidazolate framework-8 (ZIF-8) encapsulant and formamidinium iodide (FAI) are introduced between tin oxide (SnO2 ) and lead iodide (PbI2 ) layer. Intriguingly, the capsule dopant interlayer benefits the formation of porous PbI2 film due to the porous nanostructure of ZIF-8 which is favorable for the subsequent intercalation reaction. Furthermore, the constituent of the perovskite precursor in ZIF-8 pores can convert into the crystal nuclei of perovskite by reacting with PbI2 first, thereby promoting further perovskite crystallization. Significantly, the incorporation of ZIF-8 can enhance the resistance of perovskite against ultraviolet (UV) illumination due to down-conversion effect. Consequently, the modified device achieves a champion power conversion efficiency (PCE) of 24.08% and displays enhanced UV stability, which can sustain 83% of its original PCE under 365nm UV illumination for 300h. Moreover, the unencapsulated device maintains 90% of initial PCE after 1500h storage in dark ambient conditions with a relative humidity range of 50∼70%. This article is protected by copyright. All rights reserved.

Alleviating halide perovskite surface defects

Alleviating halide perovskite surface defects

Effects of the concentration of PbI2 and CH3NH3I on the perovskite films and the performance of perovskite solar cells based on ZnO-TiO2 nanorod arrays

To date the research of the effects of the concentration of PbI2 and CH3NH3I in the two-step sequential deposition process on the perovskite films and the performance of the perovskite solar cells (PSCs) based on nanorod arrays is rarely reported. In this paper, the perovskite films and the PSCs based on ZnO-TiO2 nanorod arrays were prepared by two-step sequential deposition method in ambient atmosphere. The effects of the concentration of PbI2 and CH3NH3I solution on the morphology, structure, optical absorption and luminescence properties of perovskite films and cell performance were systematically investigated by using field emission scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, fluorophotometer, and photocurrent density-voltage (J-V) curves. The best power conversion efficiency (PCE) of perovskite solar cell reaches 10.38% by using PbI2 with a concentration of 1.0 M and CH3NH3I with a concentration of 0.063 M in ambient atmosphere with a relative humidity of about 40%. The PCE of the device may be further improved by optimizing the density and length of nanorod arrays and using glove box. These results provide valuable information for preparing more efficient all-solid-state PSC based on nanorod arrays.

Tunable Crystallization and Nucleation of Planar CH3NH3PbI3 through Solvent-Modified Interdiffusion.

A smooth and compact light absorption perovskite layer is a highly desirable prerequisite for efficient planar perovskite solar cells. However, the rapid reaction between CH3NH3I methylammonium iodide (MAI) and PbI2 often leads to an inconsistent CH3NH3PbI3 crystal nucleation and growth rate along the film depth during the two-step sequential deposition process. Herein, a facile solvent additive strategy is reported to retard the crystallization kinetics of perovskite formation and accelerate the MAI diffusion across the PbI2 layer. It was found that the ultrasmooth perovskite thin film with narrow crystallite size variation can be achieved by introducing favorable solvent additives into the MAI solution. The effects of dimethylformamide, dimethyl sulfoxide, γ-butyrolactone, chlorobenzene, and diethyl ether additives on the morphological properties and cross-sectional crystallite size distribution were investigated using atomic force microscopy, X-ray diffraction, and scanning electron microscopy. Furthermore, the light absorption and band structure of the as-prepared CH3NH3PbI3 films were investigated and correlated with the photovoltaic performance of the equivalent solar cell devices. Details of perovskite nucleation and crystal growth processes are presented, which opens new avenues for the fabrication of more efficient planar solar cell devices with these ultrasmooth perovskite layers.

High-quality CH3NH3PbI3 thin film fabricated via intramolecular exchange for efficient planar heterojunction perovskite solar cells

The high-quality CH3NH3PbI3 perovskite thin film with excellent coverage and uniformity was prepared using an intramolecular exchange technology via a low-temperature, two-step sequential deposition process. The PbI2(DMSO) complex was synthesized at room temperature without any additives and was deposited, then the CH3NH3I solution was deposited subsequently. The further controllable thermal annealing process resulted in the complete formation of flat and uniform CH3NH3PbI3 thin film with large-size grains and (110) preferred crystallographic orientation. The perovskite solar cells (PSCs) with a very simple inverted planar heterojunction structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al and without other buffer layers, e.g., C60, LiF, BCP, etc., were fabricated, resulting in a power conversion efficiency (PCE) as high as 14.26%. The results suggest that the low-temperature, two-step sequential deposition process with intramolecular exchange technology provides a good route to fabricate high-quality perovskite thin film and efficient PSCs, which would match with large-scale, high-output roll-to-roll (R2R) printing/coating techniques.

Enhanced performance in hole transport material free perovskite solar cells via morphology control of PbI2 film by solvent treatment

The morphology of PbI2 film plays a critical role in determining the quality of the resultant CH3NH3PbI3 film and power conversion efficiency of CH3NH3PbI3 perovskite solar cell. Here, we propose a solvent treatment method in the two-step sequential deposition process to control the morphology of PbI2 film, which leads to enhanced power conversion efficiency. Hole transport material free perovskite solar cell is chosen as a paradigm to demonstrate this idea. Solvent (isopropanol, chlorobenzene, or ethanol) treated PbI2 films exhibit dendrite-like or flake-like morphologies, which facilitate more complete conversion of PbI2 to CH3NH3PbI3 perovskite in ambient atmosphere with a relative high humidity. Therefore, enhanced performance is obtained with the solvent treated PbI2 films. Average power conversion efficiency has been improved from 9.42% in the traditional two-step sequential deposition to 11.22% in solar cells derived from ethanol treated PbI2 films.

Controllable lasing performance in solution-processed organic–inorganic hybrid perovskites

Solution-processed organic-inorganic perovskites are fascinating due to their remarkable photo-conversion efficiency and great potential in the cost-effective, versatile and large-scale manufacturing of optoelectronic devices. In this paper, we demonstrate that the perovskite nanocrystal sizes can be simply controlled by manipulating the precursor solution concentrations in a two-step sequential deposition process, thus achieving the feasible tunability of excitonic properties and lasing performance in hybrid metal-halide perovskites. The lasing threshold is at around 230 μJ cm-2 in this solution-processed organic-inorganic lead-halide material, which is comparable to the colloidal quantum dot lasers. The efficient stimulated emission originates from the multiple random scattering provided by the micro-meter scale rugged morphology and polycrystalline grain boundaries. Thus the excitonic properties in perovskites exhibit high correlation with the formed morphology of the perovskite nanocrystals. Compared to the conventional lasers normally serving as a coherent light source, the perovskite random lasers are promising in making low-cost thin-film lasing devices for flexible and speckle-free imaging applications.

PbCl2-assisted film formation for high-efficiency heterojunction perovskite solar cells

PbCl2 is used as an additive to assist perovskite film formation in a two-step sequential deposition process and the device achieved an average efficiency enhancement of approximately 30% compared to the control group.

Improvement of CH₃NH₃PbI₃ Formation for Efficient and Better Reproducible Mesoscopic Perovskite Solar Cells.

High-performance perovskite solar cells (PSCs) are obtained through optimization of the formation of CH3NH3PbI3 nanocrystals on mesoporous TiO2 film, using a two-step sequential deposition process by first spin-coating a PbI2 film and then submerging it into CH3NH3I solution for perovskite conversion (PbI2 + CH3NH3I → CH3NH3PbI3). It is found that the PbI2 morphology from different film formation process (thermal drying, solvent extraction, and as-deposited) has a profound effect on the CH3NH3PbI3 active layer formation and its nanocrystalline composition. The residual PbI2 in the active layer contributes to substantial photocurrent losses, thus resulting in low and inconsistent PSC performances. The PbI2 film dried by solvent extraction shows enhanced CH3NH3PbI3 conversion as the loosely packed disk-like PbI2 crystals allow better CH3NH3I penetration and reaction in comparison to the multicrystal aggregates that are commonly obtained in the thermally dried PbI2 film. The as-deposited PbI2 wet film, without any further drying, exhibits complete conversion to CH3NH3PbI3 in MAI solution. The resulting PSCs reveal high power conversion efficiency of 15.60% with a batch-to-batch consistency of 14.60 ± 0.55%, whereas a lower efficiency of 13.80% with a poorer consistency of 11.20 ± 3.10% are obtained from the PSCs using thermally dried PbI2 films.

Direct Conversion of CH3NH3PbI3 from Electrodeposited PbO for Highly Efficient Planar Perovskite Solar Cells.

Organic-inorganic hybrid perovskite materials have recently been identified as a promising light absorber for solar cells. In the efficient solar cells, the perovskite active layer has generally been fabricated by either vapor deposition or two-step sequential deposition process. Herein, electrochemically deposited PbO film is in situ converted into CH3NH3PbI3 through solid-state reaction with adjacent CH3NH3I layer, exhibiting a large-scale flat and uniform thin film with fully substrate coverage. The resultant planar heterojunction photovoltaic device yields a best power conversion efficiency of 14.59% and an average power conversion efficiency of 13.12 ± 1.08% under standard AM 1.5 conditions. This technique affords a facile and environment-friendly method for the fabrication of the perovskite based solar cells with high reproducibility, paving the way for the practical application.

CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%.

Although inorganic hole-transport materials usually possess high chemical stability, hole mobility, and low cost, the efficiency of most of inorganic hole conductor-based perovskite solar cells is still much lower than that of the traditional organic hole conductor-based cells. Here, we have successfully fabricated high quality CH3NH3PbI3 films on top of a CuSCN layer by utilizing a one-step fast deposition-crystallization method, which have lower surface roughness and smaller interface contact resistance between the perovskite layer and the selective contacts in comparison with the films prepared by a conventional two-step sequential deposition process. The average efficiency of the CuSCN-based inverted planar CH3NH3PbI3 solar cells has been improved to 15.6% with a highest PCE of 16.6%, which is comparable to that of the traditional organic hole conductor-based cells, and may promote wider application of the inexpensive inorganic materials in perovskite solar cells.

A fast deposition-crystallization procedure for highly efficient lead iodide perovskite thin-film solar cells.

Thin-film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two-step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution-processed thin films yielded an average power conversion efficiency of 13.9±0.7% and a steady state efficiency of 13% under standard AM 1.5 conditions.