Properties Of Perovskite Films Research Articles

Ambient air-compatible in-situ characterizations of metal halide perovskite for high-efficiency solar cells

Abstract Long-term stability and power conversion efficiency of perovskite solar cells are strongly affected by their precursor compositions and intermediate phases during the fabrication process. In general, complex chemical reactions happen in a short time scale during the nucleation and crystal growth steps. However, the ex-situ characterization probes cannot capture the dynamics of perovskite film formation and degradation. In this review, we discussed the ambient air-compatible in-situ characterization probes that are used to monitor the evolution of the structural, morphological, and optoelectronic properties of perovskite films, which provides a deep understanding of the perovskite crystal formation process.

Ambient air-compatible in-situ characterizations of metal halide perovskite for high-efficiency solar cells

Abstract Long-term stability and power conversion efficiency of perovskite solar cells are strongly affected by their precursor compositions and intermediate phases during the fabrication process. In general, complex chemical reactions happen in a short time scale during the nucleation and crystal growth steps. However, the ex-situ characterization probes cannot capture the dynamics of perovskite film formation and degradation. In this review, we discussed the ambient air-compatible in-situ characterization probes that are used to monitor the evolution of the structural, morphological, and optoelectronic properties of perovskite films, which provides a deep understanding of the perovskite crystal formation process.

Optoelectronic properties of perovskite thin films derived from lead sulfide via radio frequency magnetron sputtering: effect of the substrate temperature

Methylammonium lead iodide (CH3NH3PbI3; MAPbI3) films were fabricated from sputtered lead sulfide (PbS) films prepared at various substrate temperatures according to the Thornton structural zone model. PbS films were converted to lead iodide (PbI2) and finally to MAPbI3 in a two-step gas-phase reaction. The increase in substrate temperature caused the morphology to change to fibrous interconnected grains, which played an important role in improving the optoelectrical properties of perovskite films. Moreover, enhanced charge transport of MAPbI3 films was observed owing to the fibrous interconnected PbI2 precursor, which was confirmed by a higher absorption coefficient and longer carrier lifetime.

Phosphonic Chloride Assisted Fabrication of Highly Emissive Mixed Halide Perovskite Films in Ambient Air for Blue Light-Emitting Diodes.

Blue perovskite light-emitting diodes (LEDs) have emerged as promising candidates for full-color display and lighting applications. However, the fabrication of blue-emitting perovskite films typically requires an inert environment, leading to increased complexity and cost in the manufacturing process, which is undesirable for applications of perovskite LEDs. Herein, we report a strategy to fabricate bright blue-emitting perovskite films in ambient air by incorporating phosphonic chlorides in a perovskite precursor solution. We used two different phosphonic chlorides, diphenylphosphonic chloride (DPPC) and phenylphosphonic dichloride (PPDC), and comparatively studied their effects on the properties of perovskite films and the blue LEDs. It is found that PPDC possesses a stronger chlorination ability due to higher hydrolysis reactivity; meanwhile, it has a stronger interaction with the perovskite compared to DPPC, resulting in an improved film quality and enhanced blue emission with a photoluminescence quantum yield of 45%, which represents the record value for the air-processed blue perovskite films. Blue perovskite LEDs are fabricated, and the emission wavelengths are effectively tuned by controlling the concentration of phosphonic chlorides. Benefiting from the optimized perovskite films with reduced nonradiative recombination and promoted charge injection and transport, the PPDC-derived blue perovskite LEDs exhibit improved performance with an external quantum efficiency of 3.3% and 1.2% for the 490 and 480 nm emission wavelength, respectively.

In Situ Synthesized Low-Dimensional Perovskite for >25% Efficiency Stable MA-Free Perovskite Solar Cells.

Developing an additive to effectively regulate the perovskite crystallization kinetics for the optimized optoelectronic properties of perovskite film plays a vital role in obtaining high efficiency and stable perovskite solar cells (PSCs). Herein, a new additive is designed and directly synthesized in perovskite precursor solution by utilizing an addition reaction between but-3-yn-1-amine hydrochloride (BAH) and formamidinium iodide. It is found that its product may control the intermediate precursor phase for regulating perovskite nucleation, leading to advantageous 2D perovskite to induce growth of perovskite along the preferred [001] orientation with not only released lattice strain but also strong interaction with perovskite to passivate its surface defects. By taking advantage of the above synergistic effects, the optimized PSC delivers an efficiency of 25.19% and a high open-circuit voltage (VOC) of 1.22 V. Additionally, the devices demonstrate good stability, remaining over 90% of their initial efficiencies under ambient atmosphere conditions for 60 days, high temperature of 85°C for 200 h, or maximum power point tracking for 500 h.

Effect of spin coat speed on structure, composition and properties of perovskite films

Recently, 2D perovskite has emerged as a promising alternative material for solar cell applications because of its superior stability in wet environments. Among the various methods for preparing 2D perovskite films, spin coat is the most widely used due to its low pollution, high accuracy and energy efficiency. In this study, the effects of spin coat speed on the surface morphology, crystal structure and surface composition of 2D perovskite (BA2MA3Pb4I13) films are investigated using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy and other techniques. It is found that the BA2MA3Pb4I13 film has large crystal size, good crystallinity and small lattice constant at a relatively low spin coat speeds. The device performance test showed that the BA2MA3Pb4I13 film can obtain better device performance as well. It indicated that the photovoltaic performance of perovskite solar cells can be significantly improved by optimization of the fabrication parameters during the film preparation process.

Uniaxial-Oriented Perovskite Films with Controllable Orientation.

Perovskite films with large crystal size, preferred orientation, and facile fabrication process, combining advantages of single-crystal and polycrystalline films, have gained considerable attention recently. However, there is little research on the facet properties of perovskite films. Here, (111)- and (001)-oriented perovskite films with bandgaps ranging from 1.53 to 1.77eV, and systematically investigated their orientation-dependent properties are achieved. The (111)-oriented films show electron-dominated traps and the (001)-oriented films show hole-dominated traps, which are related to their atomic arrangement at the surface. Compared with the (001)-oriented films, the (111)-oriented films exhibit lower work function and superior water/oxygen robustness. For the wide-bandgap films, the lattice of the (001)-oriented film provides an unobstructed passage for ion migration. Comparably, the (111)-oriented films exhibit suppressed ion migration and excellent phase stability. The optimized unencapsulated solar cells based on both (001) and (111) orientations show a similar high efficiency of ≈23%. The (111)-oriented solar cell exhibits excellent stability, maintaining 95% of its initial efficiency after 1500h maximum power point (MPP) tracking test, and 97% initial efficiency after 3000h aging in ambient conditions. This work paves the way for the rational design, controllable synthesis, and targeted optimization of uniaxial-oriented perovskite films for various electronic applications.

Mechanism of defect passivation achieved by chemical interaction in inverted perovskite solar cells

A variety of defects exist in the solution-processed polycrystalline perovskites, resulting in photovoltaic output losses and degradation. Chemical interaction is a promising way to realize the passivation of defects. Herein, cetyl pyridinium bromide (CPB) containing both pyridine units and long-chain alkyl groups was introduced in the perovskite precursor solution as a passivation agent. Experimental results show that pyridine unit in CPB formed coordination with uncoordinated Pb2+, which also interact with N–H in MAPbI3. Meanwhile, long-chain alkyl groups in CPB had interaction with MAI and PbI2 in MAPbI3. Thus, trace amount of CPB in the precursor solution improved the optoelectronic properties of perovskite films and suppressed non-radiative carrier recombination in perovskite solar cell (PSC). CPB-modified perovskite films exhibit a lower trap-state density and stronger carrier migration capability. It enables the significant enhancement of PCE values of the p-i-n structured PSC from 18.27 % to 20.53 %, accompanied by the improved stability. Our work exhibits more possibility between passivating additive and PSC performance.

Fluorescence properties and laser-induced enhancement of CsPbBr3 quantum dot with three different ligand amine systems

Inorganic perovskites have attracted much attention due to their excellent optical properties, making them a potential material for optoelectronic devices. In order to better apply it to optoelectronic devices, researchers have developed many synthesis schemes, for example, hot injection method, ligand-assisted reprecipitation method, template method, etc. to accurately control chemical composition, dimension, size, photoelectric and other properties. Here, we used oleylamine, octylamine, and phenylethylamine as amine ligands, and synthesized quantum dots (QDs) through the hot injection method. We found that quantum dot solutions prepared with long-chain ligands exhibit better luminescence performance, while quantum dot films prepared with shorter-chain phenethylamine ligands exhibit better luminescence performance, revealing the regulatory mechanism of amine ligands in the quantum dot growth process. In addition, we have enhanced the optical properties of perovskite films through laser direct writing, providing a reference for the synthesis and control of perovskite materials and their applications in the display.

The Structural, stability, electronic and optoelectronics properties of Y2AgBiX6 (Y = K, Na, li; X = I, Br, Cl) halide double Perovskites: A First-Principles study

The crystal structure, electronic and optoelectronic properties of halide double perovskites Y2AgBiX6 (Y = K, Na, Li; X = I, Br, Cl) have been studied by first principles (FPs) in this paper. According to the elastic modulus and formation energy of crystal Li2AgBiX6, its structural stability is poor. In addition, the dependence of their electronic and mechanical properties, the effective mass of carriers and light absorption on elemental composition has been analyzed, and it is inferred that these materials have good electron transport properties. The photovoltaic characteristics of halide perovskite materials (PMs) based on potassium and sodium are studied. The photovoltaic properties of perovskite films with thickness of 1 μm, 5 μm and 10 μm were further analyzed, and it was found that the absorption was the highest when the film thickness was 10 μm. The current–voltage curve of the solar cell with above perovskite as absorbing material is calculated and analyzed by first principles. The result shows that Na2AgBiBr6, Na2AgBiCl6, K2AgBiI6 and K2AgBiCl6 are predicted to have excellent photovoltaic properties. Compared to other commonly used PMs, perovskite Y2AgBiX6 (Y = K, Na, Li; X = I, Br, Cl) has a smaller effective mass, which may contribute to good carrier transport and high performance of its optoelectronic devices. The absorption curves of K2AgBiBr6, K2AgBiCl6, Na2AgBiBr6, Li2AgBiBr6, and Li2AgBiCl6 matched well with the spectral irradiance of AM 1.5. Taken together, K2AgBiBr6 and Na2AgBiBr6 are the most suitable candidates for solar cell absorption layers because of their appropriate band gap and good stability.

Unlocking The Role of Guanidinium Salts in Interface Engineering for Boosted Performance of Inverted Perovskite Solar Cells.

NiOx-based inverted perovskite solar cells (PSCs) have attracted growing attention due to their low cost and large-scale application potential. However, the efficiency and stability of inverted planar heterojunction PSCs is still unsatisfactory owing to insufficient charge-extraction caused by undesirable interfacial contact between perovskite and NiOx hole transport layers (HTLs). Herein an interfacial passivation strategy with guanidinium salts (guanidinium thiocyanate (GuASCN), guanidine hydrobromide (GuABr), guanidine hydriodate (GuAI)) as passivator is employed to solve this problem. We systematically study the effect of various guanidinium salts on the crystallinity, morphology, and photophysical properties of perovskite films. Guanidine salt as interfacial passivator can decrease interface resistance, reduce carrier non-radiative recombination, and boost carrier extraction. Notably, the GuABr-treated unencapsulated devices can still maintain more than 90 % of their initial PCE after aging for 1600 h at 16-25 °C and 35 %-50 % relative humidity in ambient conditions. This work reveals the significance of counterions in improving the photovoltaic performance and stability of PSCs.

Side‐Chain Functionalized Polymer Hole‐Transporting Materials with Defect Passivation Effect for Highly Efficient Inverted Quasi‐2D Perovskite Solar Cells

AbstractCompared with inverted 3D perovskite solar cell (PSCs), inverted quasi‐2D PSCs have advantages in device stability, but the device efficiency is still lagging behind. Constructing polymer hole‐transporting materials (HTMs) with passivation functions to improve the buried interface and crystallization properties of perovskite films is one of the effective strategies to improve the performance of inverted quasi‐2D PSCs. Herein, two novel side‐chain functionalized polymer HTMs containing methylthio‐based passivation groups are designed, named PVCz‐SMeTPA and PVCz‐SMeDAD, for inverted quasi‐2D PSCs. Benefited from the non‐conjugated flexible backbone bearing functionalized side‐chain groups, the polymer HTMs exhibit excellent film‐forming properties, well‐matched energy levels and improved charge mobility, which facilitates the charge extraction and transport between HTM and quasi‐2D perovskite layer. More importantly, by introducing methylthio units, the polymer HTMs can enhance the contact and interactions with quasi‐2D perovskite, and further passivating the buried interface defects and assisting the deposition of high‐quality perovskite. Due to the suppressed interfacial non‐radiative recombination, the inverted quasi‐2D PSCs using PVCz‐SMeTPA and PVCz‐SMeDAD achieve impressive power conversion efficiency (PCE) of 21.41% and 20.63% with open‐circuit voltage of 1.23 and 1.22 V, respectively. Furthermore, the PVCz‐SMeTPA based inverted quasi‐2D PSCs also exhibits negligible hysteresis and considerably improved thermal and long‐term stability.

Thermal Management Enables Stable Perovskite Nanocrystal Light-Emitting Diodes with Novel Hole Transport Material.

The severely insufficient operational lifetime of perovskite light-emitting diodes (LEDs) is incompatible with the rapidly increasing external quantum efficiency, even as it approaches the theoretical limit, thereby significantly impeding the commercialization of perovskite LEDs. In addition, Joule heating induces ion migration and surface defects, degrades the photoluminescence quantum yield and other optoelectronic properties of perovskite films, and induces the crystallization of charge transport layers with low glass transition temperatures, resulting in LED degradation under continuous operation. Here, a novel thermally crosslinked hole transport material, poly(FCA60 -co-BFCA20 -co-VFCA20 ) (poly-FBV), with temperature-dependent hole mobility is designed, which is advantageous for balancing the charge injection of the LEDs and limiting the generation of Joule heating. The optimised CsPbI3 perovskite nanocrystal LEDs with poly-FBV realise approximately a 2-fold external quantum efficiency increase over the LED with commercial hole transport layer poly(4-butyl-phenyl-diphenyl-amine) (poly-TPD), owing to the balanced carrier injection and suppressed exciton quenching. Moreover, because of the Joule heating control provided by the novel crosslinked hole transport material, the LED utilising crosslinked poly-FBV has a 150-fold longer operating lifetime (490min) than that utilizing poly-TPD (3.3min). The study opens a new avenue for the use of PNC LEDsin commercial semiconductor optoelectronic devices.

Effect of carbon quantum dots and Zn2+ ion on perovskite solar cells

Perovskite solar cells (PSCs) have a great attention due to their remarkable performance and a high-quality perovskite film is necessary to achieve high power conversion efficiency (PCE). The effect of carbon quantum dots (CQDs) and Zn2+ ions on perovskite layer of methyl ammonium lead iodide (MAPbI3) was investigated. The optical, structural, and morphological properties of perovskite films with different Zn2+ ratios and CQDs contents were investigated. It was observed that 1% ZnCl2 /0.05 mg/mL CQDs perovskite film composed of uniform grains distribution, complete surface coverage with negligible pinholes, and a larger grain size of 1.8 μm. In addition, it was found that increasing CQDs contents to 0.1 and 0.25 mg/mL enlarged the grain size to ~ 4.2 μm. Moreover, the incorporation of CQDs enhanced crystallinity and grain size. Consequently, these improvements were reflected on the solar cell performance and the efficiency of PSCs with additive of 1% ZnCl2-0.05 mg/mL CQDs was improved from 4.21 to 8.08%.

Performance of Cs-Doped Carbon-Based Perovskite Solar Cells in Ambient Environment

The development of organometal halide-based perovskite solar cells (PSCs) has made remarkable progress in photovoltaics. The commercialization of PSCs is still significantly limited, owing to their poor stability and the high material cost of a hole transport layer (HTL) and metal electrodes. To counter these issues, a carbon-based HTL and noble metal-free PSCs are being used. In this work, the effect of Cs-doping on perovskite film morphology and device performance has been systematically studied because the Cs+ and Br− ions-doping has proved to be a good choice to improve the stability of PSCs in combination with a carbon electrode. The results showed that when the Cs-doping concentration in perovskite film, MA1−xCsxPb(I1−yBry)3, was equal to x = 0.09, there was a substantial change in the morphological and optoelectronic properties of perovskite films. The grain size of perovskite films was improved from 70 nm (x = 0.00 control) to 170 nm (x = 0.09 Cs-doped), reducing grain boundaries. Moreover, the trap states were additionally passivated resulting in improved radiative recombinations in the perovskite film. The device fabrication was carried out in a controlled dry glovebox, with relative humidity < 40% using carbon as a counter electrode. As a result, Cs-doped PSCs showed a significant increase in efficiency (5.27%) compared to control PSCs (1.55%).

Preparation and characterization of lanthanum-based perovskite oxides LaMO3 (M=Fe, Cr, Mn) thin films by electrophoretic deposition

In this study, we report the fabrication and characterization of perovskite thin films deposited on FTO substrates via electrophoretic deposition (EPD). The x-ray diffraction (XRD) patterns showed the formation of the orthorhombic structure for and films and the trigonal structure for the film. The field-emission scanning electron microscopy (FE-SEM) micrographs revealed nano-spherical particles with an average grain size of about 50 nm covering the surface with fewer porosities compared to the other films. Moreover, the film exhibited a higher transparency in the visible region (∼84%). The estimated bandgaps of and perovskite films were found to be 2.17, 3.18, and 2.92 eV, respectively. In addition, the refractive indices of all deposited films were calculated using five empirical models that relate the refractive index to the bandgap, which consistently revealed a decrease in refractive index with an increase of bandgap energy This study holds significant implications for the field of perovskite thin films as we contribute new insights into the fabrication of lanthanum-based perovskite thin films using the EPD technique. The comprehensive characterization of microstructural, morphological, and optical properties provides valuable information for understanding the structure-property relationship in these materials. Furthermore, the determination of bandgaps and refractive indices enhances our understanding of the optical properties of perovskite films. The findings from this study pave the way for potential applications in optoelectronic devices, where fine-tuning of material properties is critical for optimal device performance.

Role of Dibenzo Crown Additive for Improving the Stability of Inorganic Perovskite Solar Cells.

Photovoltaics are being transformed by perovskite solar cells. The power conversion efficiency of these solar cells has increased significantly, and even higher efficiencies are possible. The scientific community has gained much attention due to perovskites' potential. Herein, the electron-only devices were prepared by spin-coating and introducing the organic molecule dibenzo-18-crown-6 (DC) to CsPbI2Br perovskite precursor solution. The current-voltage (I-V) and J-V curves were measured. The morphologies and elemental composition information of the samples were obtained by SEM, XRD, XPS, Raman, and photoluminescence (PL) spectroscopies. The distinct impact of organic DC molecules on the phase, morphology, and optical properties of perovskite films are examined and interpreted with experimental results. The efficiency of the photovoltaic device in the control group is 9.76%, and the device efficiency gradually increases with the increase of DC concentration. When the concentration is 0.3%, the device efficiency is the best, reaching 11.57%, short-circuit current is 14.01 mA/cm2, the open circuit voltage is 1.19 V, and the fill factor is 0.7. The presence of DC molecules effectively controlled the perovskite crystallization process by inhibiting the in-situ generations of impurity phases and minimizing the defect density of the film.

Synergistic effects of caesium closo-dodecaborate on buried interface for efficient and stable perovskite solar cells

The defects and strain of the buried SnO2/perovskite interface seriously affects the performances of n-i-p type perovskite solar cells. Herein, caesium closo-dodecaborate (B12H12Cs2) is introduced into buried interface to improve the device performances. B12H12Cs2 can passivate the bilateral defects of the buried interface, including the oxygen vacancy and uncoordinated Sn2+ defects on SnO2 side and the uncoordinated Pb2+ defects on perovskite side. Three-dimensional aromatic B12H12Cs2 can promote the interface charge transfer and extraction. [B12H12]2− can enhance the interface connection of buried interface by forming B-H---H-N dihydrogen bond and coordination bonds with metal ions. Meanwhile, the crystal properties of perovskite films can be improved and the buried tensile strain can be released by B12H12Cs2 due to the matched lattice between B12H12Cs2 and perovskite. In addition, Cs+ can diffuse into perovskite to reduce the hysteresis behavior by inhibiting the I− migration. Arising from the enhanced connection performances, passivated defects, improved perovskite crystallization, enhanced charge extraction, inhibited ions migration, released tensile strain at buried interface by B12H12Cs2, the corresponding devices yield a champion power conversion efficiency of 22.10% with enhanced stability. The stability of devices by B12H12Cs2 modification have been improved, and it can still maintain 72.5% of the original efficiency after 1440 h, while the control devices can only maintain 20% of the original efficiency after aging in air condition of 20–30% RH.

Effects of Solvent Vapor Atmosphere on Photovoltaic Performance of Perovskite Solar Cells

Tremendous efforts have been devoted to facilitating the commercialization of perovskite solar cells (PSCs) in the past decade. However, the influence of solvent vapor atmosphere on PSC device performance during its fabrication still lacks related investigations. Here, by using three commonly employed solvent vapors during the perovskite annealing process, i.e., isopropanol, chlorobenzene and dimethylformamide, we reveal the effects of atmosphere on related perovskite film properties and device performance. The results indicate that perovskite films prepared under these external solvent vapors exhibit distinct crystalline phases, morphologies and optical properties from films under normal conditions (nitrogen gas), resulting in a significant drop in power conversion efficiency from the initial 20.01% to the lowest of only ~15%. Our work highlights the importance of atmospheric effects in preparing efficient PSCs for scalable fabrication and commercialization.

Phosphorus doped carbon dots additive improves the performance of perovskite solar cells via defect passivation in MAPbI3 films

Perovskites have been widely investigated as absorber layer in photovoltaic technology owing to their excellent properties. For further enhancement of the power conversion efficiencies (PCEs) of MAPbI3 perovskite solar cells, here, we successfully synthesized phosphorus doped carbon dots (P-CQDs) by solvothermal method and investigated their effect as an additive on the perovskite film properties and photovoltaic performance. The results showed that electron-rich phosphorus can act as an excellent core unit in perovskite absorber layer to passivate defects at the surface for improved the crystallization and charge transport properties. Thanks to passivation effect of P-CQDs on perovskite films, as well as the suitable energy band gap values and optical properties of MAPbI3 layer, the device prepared with the addition of 5 vol% of P-CQDs achieved a champion PCE of 13.12% with a high fill factor (FF) of 73.44%, higher than the PCE of 10.71% with a FF of 58.81% for control device.