Two-step Sequential Deposition Research Articles

Slow-Release Effect Assisted Crystallization for Sequential Deposition Realizes Efficient Inverted Perovskite Solar Cells.

The two-step sequential deposition strategy has been widely recognized in promoting the research and application of perovskite solar cells, but the rapid reaction of organic salts with lead iodide inevitably affects the growth of perovskite crystals, accompanied by the generation of more defects. In this study, the regulation of crystal growth was achieved in a two-step deposition method by mixing 1-naphthylmethylammonium bromide (NMABr) with organic salts. The results show that the addition of NMABr effectively delays the aggregation and crystallization behavior of organic salts; thereby, the growth of the optimal crystal (001) orientation of perovskite is promoted. Based on this phenomenon of delaying the crystallization process of perovskite, the "slow-release effect assisted crystallization" is defined. Moreover, the incorporation of the Br element expands the band gap of perovskite and mitigates material defects as nonradiative recombination centers. Consequently, the power conversion efficiency (PCE) of the enhanced perovskite solar cells (PSCs) reaches 20.20%. It is noteworthy that the hydrophobic nature of the naphthalene moiety in NMABr can enhance the humidity resistance of PSCs, and the perovskite phase does not decompose for more than 3000 h (30-40% RH), enabling it to retain 90% of its initial efficiency even after exposure to a nitrogen environment for 1200 h.

Perovskite Seeding Approach of Two-Step Sequential Deposition for Efficient Solar Cells

Perovskite Seeding Approach of Two-Step Sequential Deposition for Efficient Solar Cells

Passivating Defects via Retarding the Reaction Rate of FAI and PbI2 Enables Stable Perovskite Solar Cells.

The two-step sequential deposition strategy has garnered widespread usage in the fabrication of high-performance perovskite solar cells based on FAPbI3. However, the rapid reaction between FAI and PbI2 during preparation often leads to incomplete reactions, reducing the device efficiency and stability. Herein, we introduced a multifunctional additive, 2-thiophenyl trifluoroacetone (TTA), into the FAI precursor. The incorporation of TTA has proven to be highly effective in slowing the reaction rate between FAI and PbI2, resulting in increased perovskite formation and improved efficiency and stability of the devices. TTA's CF3 groups interact with FAI via hydrogen bonding, effectively suppressing FA+ defects. The S and C═O groups share lone pair electrons with uncoordinated Pb2+, leading to a reduction in perovskite film defects and suppressing nonradiative recombination. Additionally, the CF3 groups impart hydrophobicity, protecting the perovskite film from moisture-induced erosion. As a result, the TTA-modified perovskite film achieves a Champion efficiency of 23.42% compared to the control's 21.52, with 20.58% efficiency for a 25 cm2 solar module. Remarkably, the unencapsulated Champion device retains 86% of its initial PCE after 1080 h under dark conditions (60 ± 5 °C, 35 ± 5% RH), indicating enhanced long-term stability. These findings offer a promising and cost-effective tactic for high-quality perovskite film fabrication.

Synchronous Elimination of Excess Photoinstable PbI2 and Interfacial Band Mismatch for Efficient and Stable Perovskite Solar Cells.

Eliminating the undesired photoinstability of excess lead iodide (PbI2 ) in the perovskite film and reducing the energy mismatch between the perovskite layer and heterogeneous interfaces are urgent issues to be addressed in the preparation of perovskite solar cells (PVSCs) by two-step sequential deposition method. Here, the 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4 ) is employed to convert superfluous PbI2 to more robust 1D EMIMPbI3 which can withstand lattice strain, while forming an interfacial dipole layer at the SnO2 /perovskite interface to reconfigure the interfacial energy band structure and accelerate the charge extraction. Consequently, the unencapsulated PVSCs device attains a champion efficiency of 24.28 % with one of the highest open-circuit voltage (1.19 V). Moreover, the unencapsulated devices showcase significantly improved thermal stability, enhanced environmental stability and remarkable operational stability accompanied by 85 % of primitive efficiency retained over 1500 h at maximum power point tracking under continuous illumination.

Design of a simple bifunctional system as a self-assembled monolayer (SAM) for inverted tin-based perovskite solar cells

In this work, we functionalized the ITO substrates with a series of self-assembled monolayer (SAM) molecules to improve the hole extraction ability of the electrodes and retard the charge recombination with the devices in an inverted planar p-i-n configuration. Organic molecules with simple structures, namely 4-aminobenzoic acid (AB), 4-(2-aminomethyl)benzoic acid (AM), 4-(2-aminoethyl)benzoic acid (AE), and 4-nitrobenzoic acid (NB) were chosen to functionalize the ITO substrates via simple immersion method to form hole-selective SAM on ITO. The TPSCs were fabricated according to a two-step sequential deposition approach using a co-solvent system, and the AB device was found to exhibit an attractive efficiency of power conversion (PCE) of 7.6 % while the other SAM-based devices showed poorer performance. The AB device also displayed impressive long-term storage stability by maintaining about 80 % of its initial efficiency for over 3500 h without encapsulation, in addition to a long-term (6 h) light-soaking stability, which is superior to the PEDOT: PSS-based device in ambient conditions. The SAM/perovskite interfacial characteristics were studied using UPS, EIS, and TCSPC to understand the energy levels, charge recombination, and hole-extraction nature, respectively, and to support the outstanding performance and stability of the AB device.

Enhanced Performance of Perovskite Solar Cell via Controlling Layer Thickness

In this study, Perovskite material methylammonium lead iodide (CH3NH3PbI3) was successfully fabricated using a two-step sequential solution deposition method. The precursor solution of lead iodide was first spin-coated, followed by immersing the film into a solution of CH3NH3I to form the Perovskite layer. The Perovskite material was then successfully applied as a light-harvesting material in Perovskite solar cells. The power conversion efficiency of the devices was optimized by varying TiO2 blocking layer, TiO2 mesoporous layer, and perovskite capping layer thickness. The best Perovskite solar cell exhibits a power conversion efficiency of 7.72% with a short-circuit photocurrent density JSC of 17.26 mA/cm2, an open-circuit photovoltage VOC of 0.94 V, and a fill factor of 47.6%; with the thicknesses of TiO2 blocking layer, TiO2 mesoporous layer, and perovskite capping layer of 100 nm, 200 nm, and 400 nm, respectively. The results show that Perovskite material has potential for solar cell application.

Regulate excess PbI2 distribution on perovskite film via amphiphilic surfactant for efficient and stable device

Lead iodide (PbI2) as a defect passivation in perovskite thin films can reduce halide vacancies and improve the performance of perovskite solar cells. However, excess PbI2 can hurt the device's performance. In the case of perovskite films prepared by two-step sequential deposition, excess PbI2 is distributed on the surface of perovskite film. The photo-decomposition of PbI2 and the formation of surface energy barriers can hinder charge transfer in the device, leading to reduced device performance and accelerated device degradation. Inspired by the use of surfactants to control the morphology of perovskite nanocrystals, a dual-functional surfactant (oleamide) was introduced to control the distribution of excess PbI2 on perovskite films. By adding oleamide, the aggregation distribution of PbI2 was successfully achieved at the perovskite grain boundaries (GBs), forming a Type-I band alignment and reducing the trap density, thereby prolonging the carrier lifetime. The results show that the power conversion efficiency (PCE) of the device increased from 21.23% to 23.12% after the introduction of oleamide. Compared with the control and oleamide-modified devices, the deep-level defects were reduced by about five orders of magnitude due to the Lewis-base nature of amide groups in oleamide. In addition, due to the aggregation distribution of excess PbI2 at GBs and the hydrophobicity of oleamide, the modified device showed better stability, maintaining 83% of its initial performance after 1000 h in air.

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.

Improving Crystallization and Stability of Perovskite Solar Cells Using a Low-Temperature Treated A-Site Cation Solution in the Sequential Deposition.

The two-step sequential deposition is a commonly used method by researchers for fabricating perovskite solar cells (PSCs) due to its reproducibility and tolerant preparation conditions. However, the less-than-favorable diffusive processes in the preparation process often result in subpar crystalline quality in the perovskite films. In this study, we employed a simple strategy to regulate the crystallization process by lowering the temperature of the organic-cation precursor solutions. By doing so, we minimized interdiffusion processes between the organic cations and pre-deposited lead iodide (PbI2) film under poor crystallization conditions. This allowed for a homogenous perovskite film with improved crystalline orientation when transferred to appropriate environmental conditions for annealing. As a result, a boosted power conversion efficiency (PCE) was achieved in PSCs tested for 0.1 cm2 and 1 cm2, with the former exhibiting a PCE of 24.10% and the latter of 21.56%, compared to control PSCs, which showed a PCE of 22.65% and 20.69%, respectively. Additionally, the strategy increased device stability, with the cells holding 95.8% and 89.4% of the initial efficiency even after 7000 h of aging under nitrogen or 20-30% relative humidity and 25 °C. This study highlights a promising low-temperature-treated (LT-treated) strategy compatible with other PSCs fabrication techniques, adding a new possibility for temperature regulation during crystallization.

Formamidinium Lead Iodide Perovskite Thin Films Formed by Two-Step Sequential Method: Solvent-Morphology Relationship.

Thin films made of formamidinium lead iodide (FAPbI3) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved α-phase formation for all selected solvents. An excessive amount of PbI2 found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2-0.5, 0.2-1 and 2-5 µm for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications.

Omnidirectional diffusion of organic amine salts assisted by ordered arrays in porous lead iodide for two-step deposited large-area perovskite solar cells

The porous lead iodide layer with ordered arrays structure is firstly fabricated to facilitate the omnidirectional diffusion of organic amine salts and realize high quality large-area perovskite film in two-step sequential deposition.

Modulation of nucleation and crystallization in PbI2 films promoting preferential perovskite orientation growth for efficient solar cells

PFAT promotes the secondary growth of PbI2 clusters and the early formation of favorable perovskite phases via a two-step sequential deposition approach.

Efficient Inverted Perovskite Solar Cells via Improved Sequential Deposition.

Inverted-structure metal halide perovskite solar cells (PSCs) have attractive advantages like low-temperature processability and outstanding device stability. The two-step sequential deposition method shows the benefits of easy fabrication and decent performance repeatability. Nevertheless, it is still challenging to achieve high-performance inverted PSCs with similar or equal power conversion efficiencies (PCEs) compared to the regular-structure counterparts via this deposition method. Here, an improved two-step sequential deposition technique is demonstrated via treating the bottom organic hole-selective layer with the binary modulation system composed of a polyelectrolyte and an ammonium salt. Such improved sequential deposition method leads to the spontaneous refinement of up and buried interfaces for the perovskite films, contributing to high film quality with significantly reduced defect density and better charge transportation. As a result, the optimized PSCs show a large enhancement in the open-circuit voltage by 100mV and a dramatic lift in the PCE from 18.1% to 23.4%, delivering the current state-of-the-art performances for inverted PSCs. Moreover, good operational and thermal stability is achieved upon the improved inverted PSCs. This innovative strategy helps gain a deeper insight into the perovskite crystal growth and defect modulation in the inverted PSCs based on the two-step sequential deposition method.

Ternary All-Polymer Solar Cells with Efficiency up to 18.14% Employing a Two-Step Sequential Deposition.

Achieving a finely tuned active layer morphology with a suitable vertical phase to facilitate both charge generation and charge transport has long been the main goal for pursuing the highly efficient bulk heterojunction all-polymer solar cells (all-PSCs). Herein, a solution to address the above challenge via synergistically combining the ternary blend strategy and the layer-by-layer (LbL) procedure is proposed. By introducing a synthesized polymer acceptor (PA ), PY-Cl, with higher crystallinity into the designed host acceptor PY-SSe-V, vertical phase distribution and molecular ordering of the LbL-type ternary all-PSCs can be improved in comparison to the LbL-type PM6/PY-SSe-V binary all-PSCs. The formation of the superior bulk microstructure can not only promote charge transport and extraction properties but also reduce energetic disorder and non-radiative recombination loss, thus improving all three photovoltaic parameters simultaneously. Consequently, the PM6/(PY-SSe-V:PY-Cl) ternary all-PSCs show the best efficiency of 18.14%, which is among the highest values reported to date for all-PSCs. This work provides a facile and effective LbL-type ternary strategy for obtaining high-efficiency all-PSCs.

Stable α-FAPbI3 via porous PbI2 for efficient perovskite solar cells.

Black-phase formamidinium lead iodide (FAPbI3), with a narrow bandgap and high thermal stability, has emerged as an in-demand material for highly efficient perovskite solar cells (PSCs). In a two-step sequential deposition, the PbI2 film plays an important role in the formation of a perovskite film with desirable qualities. This paper explores using N-methyl-2-pyrrolidone (NMP), a strong Lewis base, and N,N-dimethylformamide (DMF) as a mixed precursor solvent (DMF/NMP) of PbI2 and reports on preparing PbI2 films with a porous morphology by thermal treatment. Porous PbI2 films ensure the diffusion and sufficient reaction of the formamidinium iodide solution to form a smooth perovskite film. In addition, a dynamic spin coating method is also introduced to improve the uniformity of the perovskite film. Both methods yield a pure α-phase FAPbI3 film immediately in the unannealed state, which is necessary for the perovskite film to maintain phase stability. Finally, PSCs with a power conversion efficiency of 21.20% (0.13cm2) are fabricated and optimized. The unencapsulated PSCs retain 90% of the initial efficiency for 1000 hours in dry air and exhibit a good thermal stability when heated to 85 °C.

Defect control based on interfacial passivation via post-treatment of 1-ethylpyridine hydrobromide for achieving efficient and stable perovskite solar cells

The carrier recombination caused by a series of crystal defects in perovskite materials is still the main obstacle to further improve the photoelectric conversion efficiency. Herein, as an agent for interfacial engineering, 1-ethylpyridine hydrobromide (EPB) was employed to treat the FA1-xMAxPbI3-yBry perovskite film using a two-step sequential deposition method. The influence and mechanism of the post-treatment with EPB on the film properties and photovoltaic performance of the relevant perovskite solar cells (PSCs) were studied. The champion EPB-treated perovskite solar cell achieved a remarkable power conversion efficiency (PCE) of 20.71 % with an enhanced short current density (Jsc) of 24.14 mA cm−2, which is higher than that (PCE = 18.85 %, Jsc = 23.40 mA cm−2) of the pristine device without EPB. The nitrogen (N) atom in EPB exhibits a strong coordination with lead (Pb) from the perovskite, which reduces defect density and suppresses non-radiative recombination for achieving high-performance PSCs. The UV–vis and UPS results reveal that the effective passivation effect of EPB reduces the drop of the valence band between perovskite and SpiroOMeTAD, which effectively promoting the interfacial transport of carriers. As a result, The PCE of the EPB-treated device remains more than 90 % of the initial efficiency after 400 h of unpackaged and about 40 % ambient humidity.

Thermal-Radiation-Driven Ultrafast Crystallization of Perovskite Films Under Heavy Humidity for Efficient Inverted Solar Cells.

Fabricating perovskite solar cells (PSCs) in air is conducive to low-cost commercial production; nevertheless, it is rather difficult to achieve comparable device performance as that in an inert atmosphere because of the poor moisture toleration of perovskite materials. Here, the perovskite crystallization process is systematically studied using two-step sequential solution deposition in an inert atmosphere (glovebox) and air. It is found that moisture can stabilize solvation intermediates and prevent their conversion into perovskite crystals. To address this issue, thermal radiation is used to accelerate perovskite crystallization for integrated perovskite films within 10s in air. The as-formed perovskite films are compact, highly oriented with giant grain size, superior photoelectric properties, and low trap density. When the films are applied to PSC devices, a champion power conversion efficiency (PCE) of 20.8% is obtained, one of the best results for air-processed inverted PSCs under high relative humidity (60±10%). This work substantially assists understanding and modulation to perovskite crystallization kinetics under heavy humidity. Also, the ultrafast conversion strategy by thermal radiationprovides unprecedented opportunities to manufacture high-quality perovskite films for low-temperature, eco-friendly, and air-processed efficient inverted PSCs.

Heterogeneous lead iodide obtains perovskite solar cells with efficiency of 24.27%

At present, the highest power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, which exhibits great potential for commercial applications. Obtaining pinhole-free, superior crystal, and high-quality perovskite films with fewer defects by adjusting the lead iodide (PbI2) intermediate films in a two-step sequential deposition has become research arousing general interest. Herein, a heterogeneous lead iodide (HLI) structure with two (001) interplanar distances (9.0 Å and 6.9 Å), can optimize the crystallization process of perovskite to get better surface morphology and is constructed by intercalated choline chloride (a kind of vitamin B4, VB4). HLI simultaneously improves the carrier lifetime of perovskite film from 1.96 µs to 3.28 µs and reduces defect state density. Together with better morphology and lower defect state density, the open circuit voltage (VOC) and PCE based on (FAPbI3)0.97(MAPbBr3)0.03 is significantly boosted. In addition, with double-sided modification, HLI produces an excellent PCE of 24.27% with a VOC of 1.21 V. We believe that the novel heterogeneous PbI2 structure could be a generic method to improve the efficiency of PSCs.

The Potential Effect of Annealing Mesostructured Titanium Dioxide Electrode in a Closed Box Furnace on the Concentration of Lead (II) Iodide Solution Required for Optimal Performance of Mesoscopic Perovskite Solar Cells

Highly reproducible mesoscopic perovskite solar cells (PSCs) can be fabricated using two-step sequential deposition of organo-lead halide (perovskite) active layer. However, differences in the processing conditions of individual layers which are subsequently assembled to construct the ultimate device can result in variations in the solar cell performance. For instance, here we report trends in the device performance as a function of PbI2 solution concentration, where the compact and mesoporous TiO2 layers were annealed in a closed box furnace (instead of doing it in open air). We observed that the devices prepared using 1.2 M PbI2 solution concentration performed better than those prepared from 0.8 M and 1 M PbI2 solutions. Generally, the researchers use the hot plate in an open-air environment or use a special hot plate where a continuous flow of air is ensured while annealing TiO2 electron selective layers (ESL) for perovskite solar cells. In this case, the highest possible device efficiencies are achieved using 1 M concentration of PbI2 solution. Although the influence of PbI2 solution concentration has been previously studied in detail, here our prime focus is to briefly comment on slight differences in the device performance trends which we observed in comparison to the previously reported results, where TiO2 layers were calcined in open air.

Methylammonium thiocyanate seeds assisted heterogeneous nucleation for achieving high-performance perovskite solar cells

Thiocyanate (SCN-) has been reported to manage crystallization of perovskite films and improve their optoelectronic properties in solar cells. However, the mechanism of SCN- in preparation of high-quality (MAFA)Pb(IBr)3 based light-absorbing layers has not been well investigated yet. In this work, we investigate the effects of SCN- on phase transition of (MAFA)Pb(IBr)3 perovskite films and the corresponding device performance by introducing methylammonium thiocyanate (MASCN) in a PbI2 precursor solution which is used to make perovskite by a two-step sequential deposition method. Characterization of the perovskite films has shown that a proper amount (1 mg/mL) of MASCN in PbI2 can produce PbI2-MASCN seeds which act as a nucleation center for assisting heterogeneous nucleation of the (MAFA)Pb(IBr)3. Meanwhile, MASCN helps to effectively control crystallization of the perovskite film by obtaining preferential crystal growth orientation. Furthermore, MASCN is beneficial to eliminate residual PbI2 and prepare perovskite films with low trap-state density. Consequently, the power conversion efficiency (PCE) of the perovskite solar cells increases from 18.36% to 20.4%. An enhanced device stability against moisture is also observed in the MASCN-treated device which exhibits 90% retention of the initial efficiency after exposed to the ambient air for 1780 h.