Pinhole-free Perovskite Films Research Articles

Precursor Ink Engineering to Implement Vacuum Extraction Method for Scalable Production of Perovskite Solar Cells.

Engineering perovskite precursor ink to widen the processing window is crucial to obtaining uniform, compact, and pinhole-free perovskite films at scale using industrially relevant solution coating techniques. Here, we introduce a ternary solvent system and systematically investigate the impacts of coordinating solvents, N-methyl-2-pyrrolidone (NMP) and N,N'-dimethylpropyleneurea (DMPU), on the physical properties of the slot-die-coated perovskite films and on the corresponding device performance. Tailoring NMP and DMPU concentrations in the precursor ink allows us to control the perovskite intermediate phase formation and widen the processing window, enabling the reproducible production of perovskite films with high photoelectrical quality at scale. Using the optimized precursor ink, we demonstrate slot-die-coated perovskite minimodules with power conversion efficiencies of 19 and 16% on 56 and 100 cm2 substrates, respectively.

Bottom Contact Engineering for Ambient Fabrication of >25% Durable Perovskite Solar Cells.

The bottom contact in perovskite solar cells (PSCs) is easy to cause deep trap states and severe instability issues, especially under maximum power point tracking (MPPT). In this study, sodium gluconate (SG) is employed to disperse tin oxide (SnO2) nanoparticles (NPs) and regulate the interface contact at the buried interface. The SG-SnO2 electron transfer layer (ETL) enabled the deposition of pinhole-free perovskite films in ambient air and improved interface contact by bridging effect. SG-SnO2 PSCs achieved an impressive power conversion efficiency (PCE) of 25.34% (certified as 25.17%) with a high open-circuit voltage (VOC) exceeding 1.19V. The VOC loss is less than 0.34V relative to the 1.53eV bandgap, and the fill factor (FF) loss is only 2.02% due to the improved contact. The SG-SnO2 PSCs retained around 90% of their initial PCEs after 1000h operation (T90 = 1000h), higher than T80 = 1000h for the control SnO2 PSC. Microstructure analysis revealed that light-induced degradation primarily occurred at the buried holes and grain boundaries and highlighted the importance of bottom-contact engineering.

Influence of interfacial roughness on slot-die coatings for scaling-up high-performance perovskite solar cells

Slot-die coating (SDC) technology is a potential approach to mass produce large-area, high-performance perovskite solar cells (PSCs) at low cost. However, when the interface in contact with the perovskite ink has low wettability, the SDC cannot form a uniform pinhole-free perovskite film, which reduces the performance of the PSC. To address this issue, in this study, the wettability of the hole transport layer (HTL) interface was investigated in depth by analyzing the variation of wettability with process and its correlation with the roughness of the HTL interface. As a result, it was found that SDC could increase the roughness of the HTL interface to improve wettability and form a uniform high-quality perovskite layer without pinholes, and furthermore, SDC-based NiOx/Me-4PACz HTL suppressed energy losses at the HTL/perovskite interface. In addition, a unit cell achieved 19.17% of efficiency with long-term stability and lab cell-sized modules showed up to 17.42%.

Ammonium Sulfate to Modulate Crystallization for High-Performance Rigid and Flexible Perovskite Solar Cells.

Perovskite solar cells (PSCs) are attracting widespread research and attention as highly promising candidates in the field of electronic photovoltaics owing to their exceptional power conversion efficiency (PCE). However, rigid or flexible PSCs still face challenges in preparing full-coverage and low-defect perovskite films, as well as achieving highly reproducible and highly stable devices. Herein, a multifunctional additive 2-aminoethyl hydrogen sulfate (AES) is designed to regulate the film crystallization and thereby form flat and pinhole-free perovskite films. It is found that the introduction of AES can effectively passivate defects, restrain charge carrier recombination, and then achieve a higher fill factor. As seen with grazing incidence wide-angle X-ray scattering (GIWAXS), this approach does not affect the crystal orientation distribution. It is observed that AES addition shows a universality across different perovskite components since the PCE is improved up to 20.7% for FA0.97MA0.03Pb(I0.97Br0.03)3-AES, 22.85% for Cs0.05FA0.95PbI3-AES, 22.23% for FAPbI2.7Br0.3-AES, and 23.32% for FAPI-AES rigid devices. Remarkably, the non-encapsulated flexible Cs0.05 (FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 device with AES additive delivers a PCE of 20.1% and maintains over 97% of its initial efficiency under ambient conditions (25±5% relative humidity) over 2280h of aging.

Hot-Antisolvent Assisted Morphological Regulation of Perovskites for Semitransparent Photovoltaics Employing Hot-Pressing Approach

The processing of halide perovskites in the air significantly influences their morphology and surface coverage, often leading to the presence of numerous trap densities that adversely affect device performance. In this study, we explored the development of perovskite films using a solvent extraction method, where the temperature of the anisole antisolvent was varied. Our findings demonstrate that the hot-antisolvent strategy effectively controls nucleation, resulting in the formation of highly dense, pinhole-free, and crack-free perovskite films with reduced surface roughness. Films fabricated using this hot-antisolvent approach exhibited enhanced photoluminescence, indicating lower trap density and increased recombination resistance. They also showed slower charge carrier recombination rates and efficient charge extraction, suggesting the suppression of nonradiative recombination. Furthermore, the superior quality of perovskite films obtained through the hot-antisolvent strategy significantly enhanced the power conversion efficiency (PCE) of hot-pressed semitransparent perovskite solar cells. The PCE remarkably increased from 0.13% to an impressive 12.65% while maintaining an average visible transmittance of 26.55% and exceptional air stability for 2000 hours with no significant degradation in initial PCE. This study achieves a record-breaking light utilization efficiency of 3.36% in the realm of research on hot-press processes.

The synergistic effect of dry air and surfactants enables water to be a promising green solvent for stable and efficient perovskite solar cells

Through the synergistic effect of dry air and surfactants, high-quality, pinhole free perovskite films prepared from aqueous inks (Pb(NO3)2/H2O) can be easily obtained.

Green N1 additive modified perovskite precursor enables effective manufacturing of large-area solar cell modules with high efficiency and stability

Although the record power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been continuously boosted, the effective large-area manufacturing and good device stability are the major challenges toward their commercialization. Here, we report a green additive of N-methyl-2-piperidone (N1) to modify the perovskite precursor, enabling the one-step fabrication of high-quality large-area perovskite films with enhanced PCE and stability. The results show that due to the stronger complexation ability of N1 additive with PbI2, the generated PbI2-N1 complex can effectively control the nucleation and growth of perovskite to realize lead halide-framework template-assistant crystallization reaction with organic cation in the one-step solution preparation of (FAPbI3)0.95(MAPbBr3)0.05, leading to the homogeneous pinhole-free perovskite films with few defects. Therefore, the PSC device with small active-area of 0.09 cm2 exhibits an efficiency of 23.2 %. Moreover, highly efficient slot-die printed 5 × 5 cm2 PSC module has been obtained with a champion PCE of 21 % and improved device stability over 1000 h. This work demonstrates a new strategy to realize high-quality large-scale perovskite films for solution-processed PSC modules, which may be further improved and extended to other kinds of PSCs and applications such as perovskite light-emitting diodes and detectors.

Positive Feedback Mechanism of Probe Sonication for the Perovskite Films in Solar Cells.

The performance of perovskite solar cells (PSCs) is governed by the quality of perovskite films, whereby compact, pinhole-free perovskite films are desired, in addition to its composition. We have demonstrated probe sonication as a processing technique to provide positive feedback for enhancing the perovskite film quality and photovoltaic parameters, with two systems, CH3NH3PbI3 (MAPbI3) and Cs0.17FA0.83Pb(I0.83Br0.17)3. In probe sonication, the ultrasound results in the formation, growth, and collapse of the bubbles through shock wave inside the gas phase of the collapsing bubble. This phenomenon has a chemical impact on the nucleation of the perovskite phases and interconnectivity of the grains. The 60 min sonicated films with stronger hydrogen bonding network are devoid of unwanted Pb0, δ-FAPbI3, and PbI2 phases, having tightly packed homogeneous grains, minimum electron-hole recombination pathways, and improved light absorption. The surface potential remains mostly unaltered across the grains and grain boundaries, and the realignment of the Fermi energy (EF) favors facile carrier transport. The photoconversion efficiency (PCE) of the MAPbI3 and Cs0.17FA0.83Pb(I0.83Br0.17)3 devices is improved by 28.1 and 17.2% in comparison to the pristine perovskites, respectively. The 60 min sonicated Cs0.17FA0.83Pb(I0.83Br0.17)3 PSC has 20.20 ± 0.40% PCE with 1000 h ambient stability having >60% retention of the original PCE.

Two-step perovskite crystallization assisted with F-containing additives enables over 23% efficiency in perovskite solar cells

The two-step preparation of perovskite solar cells (PSCs) has attracted the interest of many researchers because this method can better control the nucleation and growth of perovskite thin films. This work proposes a crystallization management strategy to improve the quality of active layer with the assistant of F-containing additives with low boiling point. Hexafluorobenzene (HFB) is introduced into lead iodide (PbI2) precursor solutions, and HFB aggregation forms due to its low surface energies. As the result, nano porous PbI2 films are obtained after the evaporation of HFB during annealing process, leading to pinhole free perovskite films with large grain size and low defect states. As the consequence, the best power conversion efficiency (PCE) of 23.01% is obtained for the PSCs with HFB assisted perovskite films. Meanwhile HFB modified unencapsulated device maintains 88% of its initial PCE after aging for over 1440 h at 25 °C and 30% relative humidity in ambient conditions.

Valine-Modified PbI2 for the Growth of Pinhole-Free Lead Halide Perovskite Thin Films by Vapor–Solid Reaction

In recent years, the efficiency of perovskite solar cells (PSCs) has rapidly increased, making PSCs commercially viable and able to compete with silicon solar cells. However, the technology for large-scale production of perovskite thin films still poses a significant challenge to the commercialization of PSCs. This is mainly because the thickness of the perovskite light-absorbing film is less than 1 μm and easily produces pinholes during large-scale production, causing serious charge recombination and reducing the efficiency of the device. As a result, the efficiencies of most large-scale PSC modules are significantly lower than those of small-size devices. Vapor-reaction technology is considered a crucial method to enhance the uniformity of perovskite thin films. However, current techniques are not yet advanced enough to deposit pinhole-free perovskite thin films on a large scale. One major challenge is that lead iodide (PbI2) precursor thin films have a tendency to develop a sheet-like structure with a loose morphology, which contributes to the formation of pinholes in the perovskite film. Additionally, uncoordinated Pb2+ could be easily generated in the PbI2 film during thermal evaporation, causing an increase in trap-states in the perovskite crystal. To address this, we developed a valine treatment process in this study to change the preferred orientation of PbI2 from a sheet-like to a particle-like aggregate and obtained compact PbI2 thin films. Meanwhile, this valine vapor treatment can significantly reduce the uncoordinated Pb2+ in PbI2 films. Based on this, we successfully prepared pinhole-free perovskite thin films using a vapor–solid reaction. Perovskite films based on these valine-treated PbI2 exhibited a reduced trap density and significantly improved PSCs’ performance, with a maximum efficiency exceeding 21%. Large-area PSC mini-modules (5 cm × 5 cm) produced from the perovskite film (30 cm × 30 cm) showed uniformly distributed power conversion efficiency values exceeding 17%, with the highest value reaching 18.78%. We believe that this facile valine vapor treatment holds great potential for the large-scale production of stable and high-efficiency PSC modules.

Promoting Large-Area Slot-Die-Coated Perovskite Solar Cell Performance and Reproducibility by Acid-Based Sulfono-γ-AApeptide.

Homogeneous and pinhole-free large-area perovskite films are required to realize the commercialization of perovskite modules and panels. Various large-area perovskite coatings were developed; however, at their film coating and drying stages, many defects were formed on the perovskite surface. Consequently, not only the devices lost substantial performance but also their long-term stability deteriorated. Here, we fabricated a compact and uniform large-area MAPbI3-perovskite film by a slot-die coater at room temperature (T) and at high relative humidity (RH) up to 40%. The control slot-die-coated perovskite solar cell (PSC) produced 1.082 V open-circuit voltage (Voc), 24.09 mA cm-2 short current density (Jsc), 71.13% fill factor (FF), and a maximum power conversion efficiency (PCE) of 18.54%. We systematically employed a multi-functional artificial amino acid (F-LYS-S) to modify the perovskite defects. Such amino acids are more inclined to bind and adhere to the perovskite defects. The amino, carbonyl, and carboxy functional groups of F-LYS-S interacted with MAPbI3 through Lewis acid-base interaction and modified iodine vacancies significantly. Fourier transform infrared spectroscopy revealed that the C═O group of F-LYS-S interacted with the uncoordinated Pb2+ ions, and X-ray photoelectron spectroscopy revealed that the lone pair of -NH2 coordinated with the uncoordinated Pb2+ and consequently modified the I- vacancies remarkably. As a result, the F-LYS-S-modified device demonstrated more than three-fold charge recombination resistance, which is one of the primary requirements to fabricate high-performance PSCs. Therefore, the device fabricated employing F-LYS-S demonstrated remarkable PCE of 21.08% with superior photovoltaic parameters of 1.104 V Voc, 24.80 mA cm-2 Jsc, and 77.00%. FF. Concurrently, the long-term stability of the PSCs was improved by the F-LYS-S post-treatment, where the modified device retained ca. 89.6% of its initial efficiency after storing for 720 h in air (T ∼ 27 °C and RH ∼ 50-60%).

Co-Solvent Engineering Contributing to Achieve High-Performance Perovskite Solar Cells and Modules Based on Anti-Solvent Free Technology.

The pinhole-free and defect-less perovskite film is crucial for achieving high efficiency and stable perovskite solar cells (PSCs), which can be prepared by widely used anti-solvent crystallization strategies. However, the involvement of anti-solvent requires precise control and inevitably brings toxicity in fabrication procedures, which limits its large-scale industrial application. In this work, a facile and effective co-solvent engineering strategy is introduced to obtain high- quality perovskite film while avoiding the usage of anti-solvent. The uniform and compact perovskite polycrystalline films have been fabricated through the addition of co-solvent that owns strong coordination capacity with perovskite components , meanwhile possessing the weaker interaction with main solvent . With those strategies, a champion power conversion efficiency (PCE) of 22% has been achieved with the optimal co-solvent, N-methylpyrrolidone (NMP) and without usage of anti-solvent. Subsequently, PSCs based on NMP show high repeatability and good shelf stability (80% PCE remains after storing in ambient condition for 30 days). Finally, the perovskite solar module (5×5cm) with 7 subcells connects in series yielding champion PCE of 16.54%. This strategy provides a general guidance of co-solvent selection for PSCs based on anti-solvent free technology and promotes commercial application of PSCs.

Precursor engineering for efficient and stable perovskite solar cells

The perovskite film prepared by the two-step spin coating method is widely used in photovoltaic devices due to its good film morphology and great reproducibility. However, there usually exists excessive lead iodide (PbI2) in the perovskite film for this method, which is believed to passivate the grain boundaries (GBs) to increase the efficiency of the perovskite solar cells. Nevertheless, the excessive PbI2 at the GBs of perovskite is believed to induce the decomposition of the perovskite film and undermine the long-term stability of devices. In this study, we utilize precursor engineering to realize the preparation of perovskite solar cells with high efficiency and stability. The concentration of organic salts (AX: A = MA+, FA+; X = I−, Cl−) in the precursor solution for the second step of the two-step spin coating method is adjusted to optimize the perovskite light-absorbing layer so that the excessive PbI2 is converted into perovskite to obtain a smooth and pinhole-free perovskite film with high performance. Our results indicate that by adjusting the concentration of AX in the precursor solution, PbI2 in the film could be completely converted into perovskite without excessive AX residue. Both the efficiency and stability of the perovskite solar cells without excessive PbI2 have been significantly improved. A planar perovskite solar cell with the highest power conversion efficiency (PCE) of 21.26% was achieved, maintaining about 90% of the initial PCE after 300 h of storage in a dry air environment and in the dark, about 76% of the initial PCE after 300 h of continuous illumination of 1 Sun.

Enhanced device performance of Cs2AgBiBr6 double perovskite photodetector by SnO2/ZnO double electron transport layer

In this study, we report the enhancement of device performance in a lead-free perovskite Cs2AgBiBr6-based deep blue photodetector by using a SnO2/ZnO double electron transport layer (ETL). The SnO2 layer was inserted to minimize the energy loss at the interface between the ZnO ETL and perovskite absorber layer by preparation of a smooth perovskite film. The hydrophilic SnO2 layer coating on the hydrophobic ZnO nanorods provides a uniform and high-quality perovskite layer without pinholes. Reduced contact angle measurement confirmed that the surface property changes towards hydrophilicity after insertion of a SnO2/ZnO double ETL compared with bare ZnO nanorods. Moreover, the introduction of the SnO2 layer leads to better carrier transportation and extraction by matching the energy level between the perovskite and ZnO ETL. The pinhole-free perovskite film and a well-matched energy level are responsible for the Cs2AgBiBr6-based visible photodetector with a SnO2/ZnO double ETL demonstrating simultaneous improvement of responsivity and specific detectivity by 12.7 times and 16.5 times, respectively, compared with those of the ZnO single ETL. From our results, we can suggest a guideline for an interface engineering strategy to improve perovskite optoelectronic device performance.

Optimization of the Anti-Solvent Method for the Fabrication of Cu Electrode-Based High-Efficiency Perovskite Solar Cell

Organic–inorganic lead halide perovskite is promising photovoltaic energy harvesting material to fabricate high-efficiency solar cells. To enhance the power conversion efficiency (PCE) and stability of the fabricated device, a high-quality, pinhole-free, and larger grain size perovskite film is essential. Anti-solvent-assisted crystallization is a popular technique to deposit perovskite thin film. With the help of this technique, perovskite layer can be deposited with smooth surface morphology, low surface defect density, and excellent carrier transport. However, choosing a proper anti-solvent is essential for highly efficient perovskite solar cells (PvSCs). Here, we qualitatively evaluate the impacts of different anti-solvent on methylammonium lead iodide (MAPbI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) perovskite film. We used chlorobenzene (CB), diethyl ether (Eth), toluene (TL), and isopropyl alcohol (IPA) as an anti-solvent. Our result demonstrates that the anti-solvent with a relatively higher boiling point and lower polarity contributes to superior efficiency, low hysteresis, and better reproducibility of MAPbI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> active layer-based PvSCs. The device fabricated with CB anti-solvent exhibits the best PCE of 8.16% with a Cu-based electrode. This work provides a promising approach to controlling the growth and morphology of perovskite films and paves the way for further optimizing the fabrication process of large-area low-cost electrode-based high-efficiency devices.

Investigation of the Surface Coating, Humidity Degradation, and Recovery of Perovskite Film Phase for Solar-Cell Applications.

Presently, we inquire about the organic/inorganic cation effect on different properties based on structure, morphology, and steadiness in preparing a one-step solution of APbI3 thin films, where A = MA, FA, Cs, using spin coating. This study was conducted to understand those properties well by incorporating device modeling using SCAPS-1D software and to upgrade their chemical composition. X-ray diffraction (XRD) was used to analyze the crystal structures. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were conducted to characterize the surface morphology; photoluminescence, Transmission Electron Microscopy (TEM), and a UV–Visible spectrometer helped us to study the optical properties. The (110) plane is where we found the perovskite’s crystalline structure. According to the XRD results and by changing the type of cation, we influence stabilization and the growth of the absorber layer. Hither, a homogenous, smooth-surfaced, pinhole-free perovskite film and large grain size are results from the cesium cation. For the different cations, the band gap’s range, revealed by the optical analysis, is from 1.4 to 1.8 eV. Moreover, the stability of remains excellent for two weeks and in a ~60% humid environment. Based on the UV–Visible spectrometer and photoluminescence characterization, a numerical analysis for fabricated samples was also performed for stability analysis by modeling standard solar-cell structures . Modeling findings are in good agreement with experimental results that is more stable, showing a loss % in PCE of 14.28%, which is smaller in comparison to (44.46%) and (20.24%).

Effective passivation of perovkiste grain boundaries by a carboxylated polythoiphene for bright and stable Pure-Red perovskite light emitting diodes

High luminance and operative stability are essential parameters for realizing the commercialization of perovskite-based light-emitting diodes (PLEDs). However, the optoelectronic properties of PLEDs are still limited owing to the un-optimized charge transport behavior of perovskite films arising from severe defect densities and imperfect lattice structure at grain boundaries. To retrieve the morphological imperfection, we herein suggest a carboxylated polythiophene (P3CT) as a novel passivating agent of perovskite films in PLEDs. The carboxylic acid groups of P3CT enable Lewis acid-base interactions with the defective surface of perovskites such as under-coordinated Pb2+ sites or halide deficiencies, leading to efficient defect passivation and stabilization of the perovskite film surface. The P3CT-passivation successfully fabricates pinhole-free perovskite films with diminished defects at grain boundaries, bringing enhanced optoelectronic properties of red electroluminescence EL emission with a peak current efficiency and external quantum efficiency (EQE) values up to 11.15 % and 4 %, respectively. Moreover, the operative stability of the passivated PLEDs is markedly improved due to the stabilization and increased hydrophobicity of perovskite films by the inclusion of P3CT. The present findings provide a new perspective for developing stable red-PLEDs with efficient luminescence.

Selection of a Suitable Solvent Additive for 2-Methoxyethanol-Based Antisolvent-Free Perovskite Film Fabrication.

In this study, we compare various solvents with different Gutmann donor numbers as additives to improve the quality of perovskite films via an antisolvent-free process, using 2-methoxyethanol (2MOE) as the solvent. In 2MOE-based solutions, we found that the higher the donor number of the solvent, the lower the amount of the solvent required to form insoluble adducts. Furthermore, we found that N-methyl-2-pyrrolidone (NMP), which has a relatively low donor number and vapor pressure, can be added without a limitation to precipitation, while the degree of the intermediate phase in the as-deposited film is controlled by the amount of NMP added. We obtained pinhole-free and planar perovskite films by optimizing the amount of NMP added and fabricated devices based on NMP-assisted MAPbI3 and MAPbI3-xClx films, with efficiencies of 18.80 and 20.39%, respectively.

Argon-Assisted Spray-Coating Induced Efficient and Stable MAPbI3 Perovskite Solar Cells

Due to toxic antisolvents, low material utilization rate, and limitations in scalable fabrication, the spin-coating method is unsuitable for the practical application of perovskite solar cells (PSCs). This work reports an argon-assisted spray-coating process for fabricating mesoporous MAPbI3 PSCs in ambient air. We obtained pinhole-free and uniform perovskite films by optimizing the nucleation and crystallization. The optimal device’s power conversion efficiency (PCE) reached 16.34% with long-time shelf stability.

Sequential vacuum-evaporated perovskite solar cells with more than 24% efficiency.

Vacuum evaporation is promising for the high-throughput fabrication of perovskite solar cells (PSCs) because of its solvent-free characteristic, precise control of film thickness, and compatibility with large-scale production. Nevertheless, the power conversion efficiency (PCE) of PSCs fabricated by vacuum evaporation lags behind that of solution-processed PSCs. Here, we report a Cl-containing alloy-mediated sequential vacuum evaporation approach to fabricate perovskite films. The presence of Cl in the alloy facilitates organic ammonium halide diffusion and the subsequent perovskite conversion reaction, leading to homogeneous pinhole-free perovskite films with few defects. The resulting PSCs yield a PCE of 24.42%, 23.44% (certified 22.6%), and 19.87% for 0.1, 1.0, and 14.4 square centimeters (mini-module, aperture area), respectively. The unencapsulated PSCs show good stability with negligible decline in performance after storage in dry air for more than 4000 hours. Our method provides a reproducible approach for scalable fabrication of large-area, high-efficiency PSCs and other perovskite-based optoelectronics.