Grain Boundaries In Films Research Articles

Manipulating Halide Perovskite Passivation by Controlling Amino Acid Derivative Isoelectric Point for Stable and Efficient Inverted Perovskite Solar Cells

As a multigroup cross‐linking agent, amino acid derivatives contain different kinds of characteristic functional groups with different characteristics. Aiming at one of the most difficult problems, ionic defects, amino acid derivatives can passivate these defects through their multifunctional groups. Ionic defects (such as organic cations and halogen anions) mostly exist on surface and/or grain boundaries of perovskite films, and amino acid derivatives promote the formation of high‐quality perovskite films by coordinating well with these defects. Herein, the effects of two kinds of amino acids (l‐arginine and l‐glutamic acid) with contrastive isoelectric points (pIs) on perovskite film formation, defect passivation mechanism, device efficiency, flexible substrate, and thermal/moisture stability are studied. Efficiency of inverted perovskite solar cells is improved from ≈20% to nearly 23% with additives on rigid substrates. High pI l‐arginine improves the open‐circuit voltage significantly, while low pI l‐glutamic acid excels in fill factor and short‐circuit current. More importantly, low pI l‐glutamic acid shows superior thermal and moisture stability, indicating inherent stronger bonding between l‐glutamic acid and perovskite.

Efficient and Moisture-Stable Inverted Perovskite Solar Cells via n-Type Small-Molecule-Assisted Surface Treatment.

Defect states at the surface and grain boundaries of perovskite films have been known to be major determinants impairing the optoelectrical properties of perovskite films and the stability of perovskite solar cells (PeSCs). Herein, an n-type conjugated small-molecule additive based on fused-unit dithienothiophen[3,2-b]-pyrrolobenzothiadiazole-core (JY16) is developed for efficient and stable PeSCs, where JY16possesses the same backbone as the widely used Y6but with long-linear n-hexadecyl side chains rather than branched side chains. Upon introducing JY16into the perovskite films, the electron-donating functional groups of JY16passivate defect states in perovskite films and increase the grain size of perovskite films through Lewis acid-base interactions. Compared to Y6, JY16exhibits superior charge mobility owing to its molecular packing ability and prevents decomposition of perovskite films under moisture conditions owing to their hydrophobic characteristics, improving the charge extraction ability and moisture stability of PeSCs. Consequently, the PeSC with JY16shows a high power conversion efficiency of 21.35%, which is higher than those of the PeSC with Y6 (20.12%) and without any additive (18.12%), and outstanding moisture stability under 25% relative humidity, without encapsulation. The proposed organic semiconducting additive will prove to be crucial for achieving highly efficient and moisture stable PeSCs.

Simultaneous Lattice Engineering and Defect Control via Cadmium Incorporation for High-Performance Inorganic Perovskite Solar Cells.

Doping of all-inorganic lead halide perovskites to enhance their photovoltaic performance and stability has been reported to be effective. Up to now most studies have focused on the doping of elements in to the perovskite lattice. However, most of them cannot be doped into the perovskite lattice and the roles of these dopants are still controversial. Herein,the authors introduce CdI2 as an additive into CsPbI3-x Brx and use it as active layer to fabricate high-performance inorganic perovskite solar cells (PSCs). Cd with a smaller radius than Pb can partially substitute Pb in the perovskite lattice by up to 2 mol%. Meanwhile, the remaining Cd stays on the surface and grain boundaries (GB) of the perovskite film in the form of Cs2 CdI4-x Br-x , which is found to reduce non-radiative recombination. These effects result in prolonged charge carrier lifetime, suppressed defect formation, decreased GBs, and an upward shift of energybands in the Cd-containing film. A champion efficiency of 20.8% is achieved for Cd-incorporated PSCs, together with improved device ambient stability. This work highlights the importance of simultaneous lattice engineering, defectcontrol and atomic-level characterization in achieving high-performance inorganic PSCs with well-defined structure-property relationships.

Vertical distribution of PbI2 nanosheets for robust air-processed perovskite solar cells

The fabrication of perovskite solar cells (PSCs) in ambient air is technologically favorable for commercialization, however, the photovoltaic performance of ambient-processed PSCs is still lagging behind their inert counterparts. One major challenge is the growth of high-quality perovskite films regardless of the ambient humidity. Here, we demonstrate an effective strategy to grow robust perovskite film with enlarged grain size, enhanced crystallinity, and preferred orientation in high-humidity air. More particularly, PbI2 2D nanosheets are formed and vertically distributed at the grain boundaries of perovskite films, playing a powerful passivation role. Upon our regulation of the crystallization of perovskite film and the distribution of PbI2, the according device shows significant improvement in efficiency and stability. As a result, we achieve a maximum power conversion efficiency (PCE) of 19.83% for MAPbI3-based device and over 21% for MA0.6FA0.4PbI3-based device. Moreover, these devices display remarkably improved operational stability in ambient air without encapsulation. This work provides a reliable and cost-effective strategy for the commercial manufacturing of PSCs.

Laser Processing of KBr‐Modified SnO2 for Efficient Rigid and Flexible Ambient‐Processed Perovskite Solar Cells

A combination of KBr modification and laser processing is utilized to prepare SnO2 films for rigid and flexible perovskite solar cells (PSCs). The KBr modification effectively passivates the defects at the interface between SnO2 and perovskite as well as grain boundaries of the perovskite film. A power conversion efficiency (PCE) of 20.14% is achieved with the KBr‐modified SnO2 for the rigid PSCs fabricated under a relative humidity of around 65–75%, compared to the pristine SnO2 films with a PCE of 18.66%. Then, a picosecond ultraviolet laser is employed to process KBr‐modified SnO2 films on flexible substrates with a rapid scanning rate of 100 mm s−1. The laser process improves the PCEs and durability of the PSCs. The flexible PSCs fabricated by the laser remain over 80% of their initial PCEs after 1000 bending cycles, higher than those fabricated by the hot plate showing 40% of their initial PCEs after the same bending cycles.

Multifunctional Ionic Fullerene Additive for Synergistic Boundary and Defect Healing of Tin Perovskite to Achieve High-Efficiency Solar Cells.

A series of new ionic fullerene derivatives (C60-RNH3-X; X = Cl, Br, or I) were designed especially for using as additives for tin perosvkite (TPsk, with chemical formula of FA0.98EDA0.01SnI3) to form TPsk-C60-RNH3-X bulk heterojunction (BHJ) films. Inverted tin-perovskite solar cells (TPSCs) based on BHJ TPsk-C60-RNH3-Br absorber achieved the highest power conversion efficiency up to 11.74% with very high FF of 73%, without current hysteresis and stable in a glovebox. The designed spherical ionic fullerene halide additive, sitting in the grain boundaries of the TPsk film, can not only improve the quality of the TPsk film and change the valence band energy to match better with the PEDOT:PSS hole transporter but also be a carrier transporting connector between tin-perovskite grains, the defects/traps passivation/healing agent by interacting with Sn2+ ions and filling the halogen vacancies. The functions of the ionic fullerene halide additive were revealed with XRD patterns, SEM images, element mapping, UPS spectra, infrared spectra, AFM, and SCLC data. Being able to passivate newly generated defects during device operation or sitting on the shelf is an important step to improve the long-term stability of TPSCs. If a passivation agent can move dynamically during cell operation or storage to heal the defects of perovskite, the instability problem of TPSCs can be alleviated. The spherical ionic fullerene halide could be one of the ideal passivation agents satisfying this purpose.

Polypropylene Glycol‐Modified Anode Interface for High‐Performance Perovskite Solar Cells†

Comprehensive SummaryThe surface properties and chemical interactions are critical for perovskite solar cells (PVSCs). In this work, we show that the polypropylene glycol (PPG) can simultaneously passivate the NiOx surface and grain boundaries of perovskite films, allowing more efficient charge transfer at the anode interface and reducing the recombination of PVSCs. As a result, the open‐circuit voltage (Voc) of MAPbI3 based inverted PVSCs increases from 1.087 V to 1.127 V, and the short‐circuit current density (Jsc) is increased from 20.87 mA·cm–2 to 22.32 mA·cm–2, thereby realizing the improvement of the device power conversion efficiency (PCE) from 18.34% to 20.12%. Moreover, the steady‐state output of the PVSCs is remarkably improved by incorporating PPG. Further analysis of surface properties suggests that part of the PPG at the interface can permeate into the precursor solution with the help of DMF solvent and remain in the perovskite layer to form a concentration gradient. The ether bond of PPG and the uncoordinated Pb2+ in the perovskite are coordinated to achieve passivation effects and improve device performance. Our work provides a rational strategy for the preparation of high‐performance PVSCs.

Passivation of surface defects in FAPbI3 perovskite by methimazole molecule: A first-principles investigation

There are a large number of defects existing on the surfaces and grain boundaries of perovskite film, which cause the reduction of power conversion efficiency and accelerate the degradation of solar cell devices. Herein, based on the first-principles of density functional theory calculations, we proposed two defect passivation modes, defect-inhibiting mode and defect-healing mode, to explore the passivation effect and mechanism of methimazole (MMI) molecule on the surface defects of formamidinium lead triiodide (FAPbI3). Our calculations show that MMI molecule can stably adsorb on the FAPbI3 (001) surface by forming Pb−S coordination bond and I···H hydrogen bond. In the defect-inhibiting mode, the chemical statuses of under-coordinated Pb and I ions on the perovskite surfaces are alleviated by the MMI adsorption, leading to the increase of defect formation energy and thus inhibiting the formation of surface defects. In the defect-healing mode, the S atom in MMI molecule provides its lone pair electrons to fill the defect states introduced by the surface defects, eliminating or reducing the defect states near the band edge or in the bandgap. This study gives a deep understanding for the passivation mechanism of small organic molecule on the surface defects of perovskite and provides an effective strategy of surface passivation for improving the performance of perovskite solar cells.

Perovskite nanowires as defect passivators and charge transport networks for efficient and stable perovskite solar cells

The problems posed by the presence of ionic defects on the surface and at the grain boundaries of perovskite films must be solved before the power conversion efficiency of organic–inorganic halide perovskite solar cells can be enhanced. While a number of strategies to address this problem have been developed, the challenge of achieving both effective passivation and charge transporting performance remains. In this paper, inorganic perovskite nanomaterials, shaped into nanowires (NWs), were introduced as a strategy to passivate defects at the grain boundaries and facilitate charge transport across the interfacial charge transport layer. The NW-modified perovskite film significantly reduced defect sites and extended carrier lifetime compared to quantum dot-modified and pristine perovskite films, reducing non-radiative recombination significantly. The perovskite solar cells passivated with NWs achieved a power conversion efficiency of 21.56% and improved device stability over a 3500-hour period.

SnO2 electron transport layer modified with gentian violet for perovskite solar cells with enhanced performance

Interface engineering is a feasible strategy to passivate the defects located at both the surfaces and grain boundaries of the perovskite films. In this work, gentian violet, which is composited of a positive charged amine group and a negative charged Cl − ion, is selected to engineer the MAPbI 3 /SnO 2 interface. The gentian violet modified SnO 2 film can enhance the crystallinity of the subsequently deposited MAPbI 3 perovskite film, at the same time, due to the effective defect passivation capability of the gentian violent, the trap density of the perovskite film is suppressed. Therefore, the target perovskite solar cell has shown a maximum performance of 20.03% after tuning the concentration of gentian violet. • Gentian violet modified SnO 2 film can enhance the crystallinity of perovskite film. • Gentian violet modification can effectively suppress the defect density of perovskite film. • Gentian violet modification can boost the performance of PSC to 20.03%.

2D Ruddlesden-Popper perovskite ferroelectric film for high-performance, self-powered and ultra-stable UV photodetector boosted by ferro-pyro-phototronic effect and surface passivation

2D Ruddlesden-Popper (RP) perovskites have attracted enormous attention in optoelectronic fields compared with their 3D counterparts. However, most of the reported perovskite ferroelectrics-based self-powered photodetectors (PDs) are fabricated from bulk single crystals rather than perovskite thin films with improved reproducibility, flexibility, and less preparation time. Nevertheless, the defect sites at surfaces and grain boundaries of 2D perovskites polycrystalline films make them vulnerable to humidity. Herein, the highly crystallized 2D RP perovskite ferroelectric films are successfully obtained. Then, a passivation method is applied on 2D perovskite film by an in-situ reaction with 4-fluoro-phenylethylamine iodide (4-FPEAI), which reduces the defect sites and endows the perovskite films with the outstanding hydrophobic property. Then, the as-prepared 2D-perovskite ferroelectric thin films were fabricated into self-powered PDs. Boosted by the ferro-pyro-phototronic effect, the self-powered PDs demonstrate excellent optoelectronic performances at 360 nm, with dark current less than 1 × 10−12 A, a peak responsivity over 1 A W−1, a detectivity of 1.5 × 1014 Jones and fast response/recovery speed. The photoresponsivity and specific detectivity are both enhanced by 67.8 times regarding the relative peak-to-peak current, compared with those only based on the photovoltaic induced photocurrent. Further, the PDs show high stability towards high humidity and thermal treatment.

Strong room temperature exciton photoluminescence in electrochemically deposited Cu2O films

Strong room temperature exciton photoluminescence (PL) has been observed in copper (I) oxide films electrochemically deposited in a tartrate electrolyte. The PL intensity of these films is two orders of magnitude higher than that of films deposited from the classical lactate electrolyte. X-ray diffraction (XRD) and Raman spectroscopy analyses demonstrate that the films prepared using tartrate electrolyte are characterized by higher grain size, which reduces a non-radiative recombination of charge carriers. Better optical quality of the Cu2O films prepared using tartrate electrolyte is explained taking into account stronger tartrate-copper complexes, which results in lower density of grain boundaries in such films. Moreover, higher buffering capacity of the tartrate complex provides stability of pH value in the diffusion layer of the near-electrode space preventing defect formation. Our study demonstrates the promise of using Cu2O films deposited from tartrate solution for solar energy applications like photoelectric energy conversion, hydrogen production, and photocatalysis.

Dopant‐Free Phthalocyanine Hole Conductor with Thermal‐Induced Holistic Passivation for Stable Perovskite Solar Cells with 23% Efficiency

AbstractSimultaneous passivation of the defects at the surface and grain boundaries of perovskite films is crucial to achieve efficient and stable perovskite solar cells (PSCs). It is highly desirable to accomplish the above passivation through rational engineering of hole transport materials (HTMs) in combination with appropriate procedure optimization. Here, methylthiotriphenylamine‐substituted copper phthalocyanine (SMe‐TPA‐CuPc) is reported as a dopant‐free HTM for PSCs, exhibiting excellent efficiency, and stability. After thermal annealing, SMe‐TPA‐CuPc molecules diffused into the bulk of the perovskite film and effectively passivated the defects in the bulk and at the interface of the perovskite, owing to the strong interaction between the methylthio moiety and undercoordinated lead. The best‐performing annealed SMe‐TPA‐CuPc‐based device shows efficiency of 21.51%, which is higher than the unannealed SMe‐TPA‐CuPc‐based device (power‐conversion efficiency (PCE) of 20.75%) and reference doped spiro‐OMeTAD‐based device (PCE of 20.61%). Further modification of the perovskite of the annealed SMe‐TPA‐CuPc‐based device by the QAPyBF4 additive result in even higher efficiency of 23.0%. It also shows excellent stability, maintaining 96% of its initial efficiency after 3624 h aging at 85 °C. This work highlights the great potential of phthalocyanine‐based dopant‐free HTMs and the defect passivation by thermal‐induced molecular diffusion strategy for developing highly efficient and stable PSCs.

Defects passivation via d-glucosamine hydrochloride for highly efficient and stable perovskite solar cells

The defects existing on surface and grain boundaries in organic-inorganic halide perovskite films are detrimental to both the performance and stability of perovskite solar cells (PVSCs). Here, an additive of Glucosamine hydrochloride (D-GH) is introduced into the perovskite precursor solution to achieve high power conversion efficiency (PCE) and long-term stability. It is found that D-GH additive can significantly improve of the quality of perovskite film with enhanced crystallinity, compact and smooth surface and slightly enlarged grain size, leading to reduced grain boundaries, trap densities and thus negligible hysteresis in the resultant PVSCs. The optimized devices with 0.05 mg/ml D-GH additive show the best device performance with an enhanced PCE of 20.30%, as compared to the control devices with the highest PCE of 17.77%. In addition, the stability of PVSCs with 0.05 mg/ml D-GH modification is much better than that of the reference one. Overall, this work demonstrates a green and cheap additive to fabricate highly efficient and stable PVSCs. • Glucosamine hydrochloride (D-GH) was introduced into perovskite precursor solution to improve the performance of PVSCs. • The D-GH additive can significantly improve the quality of perovskite film and reduced trap densities. •. The device with D-GH as additive shows enhanced performance with PCE of 20.30%. •The stability of PVSCs with D-GH modification is much better than that of the reference one.

Revealing and Controlling Energy Barriers and Valleys at Grain Boundaries in Ultrathin Organic Films.

In organic electronics, local crystalline order is of critical importance for the charge transport. Grain boundaries between molecularly ordered domains are generally known to hamper or completely suppress charge transfer and detailed knowledge of the local electronic nature is critical for future minimization of such malicious defects. However, grain boundaries are typically hidden within the bulk film and consequently escape observation or investigation. Here, a minimal model system in form of monolayer-thin films with sub-nm roughness of a prototypical n-type organic semiconductor is presented. Since these films consist of large crystalline areas, the detailed energy landscape at single grain boundaries can be studied using Kelvin probe force microscopy. By controlling the charge-carrier density in the films electrostatically, the impact of the grain boundaries on charge transport in organic devices is modeled. First, two distinct types of grain boundaries are identified, namely energetic barriers and valleys, which can coexist within the same thin film. Their absolute height is found to be especially pronounced at charge-carrier densities below 1012 cm- 2 -the regime at which organic solar cells and light emitting diodes typically operate. Finally, processing conditions by which the type or energetic height of grain boundaries can be controlled are identified.

Microstructure and properties of La-doped Er2O3 anti-reflection films on CVD diamond

The composition and microstructure consisting of anti-reflection films was obtained by the power of magnetron sputtering. X-ray photoelectron spectroscopy (XPS) and High-resolution transmission electron microscopy (HRTEM) provided evidence to support that the doping La element exists as oxide in the grain boundaries of the matrix Er2O3 films. The undoped and La-doped Er2O3 films show a columnar crystal structure of the main cubic (222) plane. Twinning and a large number of dislocations show up in the undoped Er2O3 films due to the competitive growth of the columnar crystal. In addition, the La-doped Er2O3 films show a lower roughness (RMS) value in comparison with undoped Er2O3 films. The grain size of columnar crystals decreases significantly with increasing La concentration in the La-doped Er2O3 films. The fine grains resulted in the La-doped Er2O3 films developing high mechanical and impact resistance properties, with an increase in hardness from 12.6 ± 2.1 GPa to 26.1 ± 3.4 GPa and the eroding area rate decreasing from 38.9 % to 1.9 %. Moreover, the La-doped Er2O3 anti-reflection films on the chemical vapor deposition (CVD) diamond substrate maintained 74 % transmittance in the long-wavelength infrared range of 8–12 μm after sand eroding.

Carbazole-Containing Polymer-Assisted Trap Passivation and Hole-Injection Promotion for Efficient and Stable CsCu2 I3 -Based Yellow LEDs.

Perovskite light‐emitting diodes (LEDs) are emerging light sources for next‐generation lighting and display technologies; however, their development is greatly plagued by difficulty in achieving yellow electroluminescence, environmental instability, and lead toxicity. Copper halide CsCu2I3 with intrinsic yellow emission emerges as a highly promising candidate for eco‐friendly LEDs, but the electroluminescent performance is limited by defect‐related nonradiative losses and inefficient charge transport/injection. To solve these issues, a hole‐transporting poly(9‐vinlycarbazole) (PVK)‐incorporated engineering into CsCu2I3 emitter is proposed. PVK with carbazole groups is permeated at the grain boundaries of CsCu2I3 films by interacting with the uncoordinated Cu+, reducing the CuCs and CuI antisite defects to increase the radiative recombination and enhancing the hole mobility to balance the charge transport/injection, resulting in substantially enhanced device performances. Eventually, the yellow LEDs exhibit an 8.5‐fold enhancement of external quantum efficiency, and the half‐lifetime reaches 14.6 h, representing the most stable yellow LEDs based on perovskite systems reported so far.

Ionic Liquid-Assisted Crystallization and Defect Passivation for Efficient Perovskite Solar Cells with Enhanced Open-Circuit Voltage.

Perovskite materials have demonstrated many excellent properties in next-generation photovoltaic devices, but the intrinsic defects and the quality of perovskite film still limit the performance and stability of PSCs. Here, 1,3-dimethylimidazolium iodide (DMII) ionic liquid was employed as an additive to passivate the various defects and produce the high-quality perovskite film with enlarged grain sizes. DMII could act as an "ionic stabilizer" for passivating the point defects including the vacancies defects of organic cations and halogen anions of perovskite. At the same time, the extra problematic PbI2 on surfaces and at grain boundaries of the perovskite film could also be reacted by DMII, leading to the reduction of recombination centers and trap states. On the other hand, the DMII ionic liquid with a "Ostwald ripening effect" could retard the crystallization process of perovskite crystals and yield better film quality with higher crystallinity, smoother morphology and larger grains. As a result, the optimal device achieved a champion power conversion efficiency (PCE) of 20.4 %. Particularly, the modified devices demonstrated a significant elevation in open-circuit voltage from 1.03 to 1.10 V. The hydrophobicity of perovskite films modified by DMII was enhanced and the un-encapsulated DMII devices retained 91 % of their initial PCE after aging 60 days under 15±5 % relative humidity.

Impact of Halide Anions in CsX (X = I, Br, Cl) on the Microstructure and Photovoltaic Performance of FAPbI3‐Based Perovskite Solar Cells

The key role of Cs cation and X halide anions (X = I, Br, Cl) on the microstructure, crystal structure, structural defects, optoelectronic properties, and photovoltaic parameters of FAPbI3‐based perovskite solar cells is investigated. The CsCl–FAPbI3 perovskite film shows the highest photoluminescence (PL) intensity, longest PL lifetime, and highest power conversion efficiency compared with the CsI–FAPbI3 and CsBr–FAPbI3 perovskite films. The morphology and crystallography of c nanotwins and stacking faults of perovskite films are studied using transmission electron microscopy and selected‐area electron diffraction. The microstructure, crystallography, and atomic structure model of intersecting twin boundaries are presented. Finally, the degradation pathways and the mechanism behind the formation of FAPbI3‐based perovskites under ambient conditions are systematically studied. The grain boundaries of the perovskite films are nonuniformly damaged, resulting in many black nanoparticles after 4 weeks. Electron diffraction analyses of the black nanoparticles confirm the hexagonal PbI2 phase formation in all CsX–FAPbI3 perovskite samples after 4 weeks of aging.

Non-blockage of atomic-scale active sites in photocatalytic TiO2 thin films deposited on silica-based substrates

The present work delivers an in-depth analysis on contamination and active site blockage of anatase thin films deposited on three types of SiO2-based glass substrates using high-resolution XPS and ICP-MS. Further, the photocatalytic performance of the thin films before and after purification were analysed by UV–Vis spectrophotometry. The results reveal that ionic contaminants including alkalies (Na), alkaline earths (Mg, Ca), Al, Si, and F (and probably B) diffuse from the substrates into the grain boundaries of the thin films and represent potential sources of active site blockage. The long-term leaching in aqueous-based medium showed the entire removal of the contaminants. It was also revealed that the kinetics of leaching are controlled not by the ionic sizes or valences of the contaminant ions but by their solubilities, which are confirmed by theoretical thermodynamic study and speciation diagrams for soluble species deriving from the three types of substrates.