Showing papers on "Thin film published in 2021"

Perovskite solar cells with atomically coherent interlayers on SnO2 electrodes.

Abstract: In perovskite solar cells, the interfaces between the perovskite and charge-transporting layers contain high concentrations of defects (about 100 times that within the perovskite layer), specifically, deep-level defects, which substantially reduce the power conversion efficiency of the devices1–3. Recent efforts to reduce these interfacial defects have focused mainly on surface passivation4–6. However, passivating the perovskite surface that interfaces with the electron-transporting layer is difficult, because the surface-treatment agents on the electron-transporting layer may dissolve while coating the perovskite thin film. Alternatively, interfacial defects may not be a concern if a coherent interface could be formed between the electron-transporting and perovskite layers. Here we report the formation of an interlayer between a SnO2 electron-transporting layer and a halide perovskite light-absorbing layer, achieved by coupling Cl-bonded SnO2 with a Cl-containing perovskite precursor. This interlayer has atomically coherent features, which enhance charge extraction and transport from the perovskite layer, and fewer interfacial defects. The existence of such a coherent interlayer allowed us to fabricate perovskite solar cells with a power conversion efficiency of 25.8 per cent (certified 25.5 per cent)under standard illumination. Furthermore, unencapsulated devices maintained about 90 per cent of their initial efficiency even after continuous light exposure for 500 hours. Our findings provide guidelines for designing defect-minimizing interfaces between metal halide perovskites and electron-transporting layers. An atomically coherent interlayer between the electron-transporting and perovskite layers in perovskite solar cells enhances charge extraction and transport from the perovskite, enabling high power conversion efficiency.

Two-dimensional Ruddlesden–Popper layered perovskite solar cells based on phase-pure thin films

Abstract: Two-dimensional Ruddlesden–Popper layered metal-halide perovskites have attracted increasing attention for their desirable optoelectronic properties and improved stability compared to their three-dimensional counterparts. However, such perovskites typically consist of multiple quantum wells with a random well width distribution. Here, we report phase-pure quantum wells with a single well width by introducing molten salt spacer n-butylamine acetate, instead of the traditional halide spacer n-butylamine iodide. Due to the strong ionic coordination between n-butylamine acetate and the perovskite framework, a gel of a uniformly distributed intermediate phase can be formed. This allows phase-pure quantum well films with microscale vertically aligned grains to crystallize from their respective intermediate phases. The resultant solar cells achieve a power conversion efficiency of 16.25% and a high open voltage of 1.31 V. After keeping them in 65 ± 10% humidity for 4,680 h, under operation at 85 °C for 558 h, or continuous light illumination for 1,100 h, the cells show <10% efficiency degradation. Two-dimensional Ruddlesden–Popper layered metal-halide perovskites show better performance over three-dimensional versions, but are typically based on quantum wells with random width distribution. Liang et al. show that introducing molten salt spacers gives phase-pure quantum wells and improved solar cell performance.

Thin-Film Silicon Solar Cells

Abstract: This chapter covers the current use and challenges of thin-film silicon solar cells, including conductivities and doping, the properties of microcrystalline silicon (the role of the internal electric field, shunts, series resistance problems, light trapping), tandem and multijunction solar cells (a-Si:H/a-Si:H tandems, triple-junction amorphous cells, microcrystalline–amorphous or “micromorph” tandems), module production (deposition of thin-film layers, substrate materials, laser scribing, cell interconnection, and module encapsulation), and module performance.

Interfacial toughening with self-assembled monolayers enhances perovskite solar cell reliability

Abstract: Iodine-terminated self-assembled monolayer (I-SAM) was used in perovskite solar cells (PSCs) to achieve a 50% increase of adhesion toughness at the interface between the electron transport layer (ETL) and the halide perovskite thin film to enhance mechanical reliability. Treatment with I-SAM also increased the power conversion efficiency from 20.2% to 21.4%, reduced hysteresis, and improved operational stability with a projected T80 (time to 80% initial efficiency retained) increasing from ~700 hours to 4000 hours under 1-sun illumination and with continuous maximum power point tracking. Operational stability-tested PSC without SAMs revealed extensive irreversible morphological degradation at the ETL/perovskite interface, including voids formation and delamination, whereas PSCs with I-SAM exhibited minimal damage accumulation. This difference was attributed to a combination of a decrease in hydroxyl groups at the interface and the higher interfacial toughness.

Distribution control enables efficient reduced-dimensional perovskite LEDs.

Abstract: Light-emitting diodes (LEDs) based on perovskite quantum dots have shown external quantum efficiencies (EQEs) of over 23% and narrowband emission, but suffer from limited operating stability1. Reduced-dimensional perovskites (RDPs) consisting of quantum wells (QWs) separated by organic intercalating cations show high exciton binding energies and have the potential to increase the stability and the photoluminescence quantum yield2,3. However, until now, RDP-based LEDs have exhibited lower EQEs and inferior colour purities4–6. We posit that the presence of variably confined QWs may contribute to non-radiative recombination losses and broadened emission. Here we report bright RDPs with a more monodispersed QW thickness distribution, achieved through the use of a bifunctional molecular additive that simultaneously controls the RDP polydispersity while passivating the perovskite QW surfaces. We synthesize a fluorinated triphenylphosphine oxide additive that hydrogen bonds with the organic cations, controlling their diffusion during RDP film deposition and suppressing the formation of low-thickness QWs. The phosphine oxide moiety passivates the perovskite grain boundaries via coordination bonding with unsaturated sites, which suppresses defect formation. This results in compact, smooth and uniform RDP thin films with narrowband emission and high photoluminescence quantum yield. This enables LEDs with an EQE of 25.6% with an average of 22.1 ±1.2% over 40 devices, and an operating half-life of two hours at an initial luminance of 7,200 candela per metre squared, indicating tenfold-enhanced operating stability relative to the best-known perovskite LEDs with an EQE exceeding 20%1,4–6. The efficiency and operating lifetimes of perovskite light-emitting diodes is improved by using a fluorinated triphenylphosphine oxide additive to control the cation diffusion during film deposition and passivate the surface.

One-Step Synthesis of SnI 2·(DMSO) x Adducts for High-Performance Tin Perovskite Solar Cells

Abstract: Contemporary thin-film photovoltaic (PV) materials contain elements that are scarce (CIGS) or regulated (CdTe and lead-based perovskites), a fact that may limit the widespread impact of these emerging PV technologies. Tin halide perovskites utilize materials less stringently regulated than the lead (Pb) employed in mainstream perovskite solar cells; however, even today's best tin-halide perovskite thin films suffer from limited carrier diffusion length and poor film morphology. We devised a synthetic route to enable in situ reaction between metallic Sn and I2 in dimethyl sulfoxide (DMSO), a reaction that generates a highly coordinated SnI2·(DMSO)x adduct that is well-dispersed in the precursor solution. The adduct directs out-of-plane crystal orientation and achieves a more homogeneous structure in polycrystalline perovskite thin films. This approach improves the electron diffusion length of tin-halide perovskite to 290 ± 20 nm compared to 210 ± 20 nm in reference films. We fabricate tin-halide perovskite solar cells with a power conversion efficiency of 14.6% as certified in an independent lab. This represents a ∼20% increase compared to the previous best-performing certified tin-halide perovskite solar cells. The cells outperform prior earth-abundant and heavy-metal-free inorganic-active-layer-based thin-film solar cells such as those based on amorphous silicon, Cu2ZnSn(S/Se)4 , and Sb2(S/Se)3.

GaN and Related Materials

Abstract: 1. Plate Type Exchangers 2. Dynamic Systems 3. A Historical Survey of Research on Gallium Nitride 4. Growth of Group III Nitrides from Molecular Beams 5. Ternary Alloys 6. Optical Characterization of GaN and Related Materials 7. Theoretical Studies in GaN 8. GaAsN Alloys and GaN/GaAs Thin Layer Structures 9. The Contribution of Defects to the Electrical and Optical Properties of GaN 10. Growth of GaN Single Crystals Under High Nitrogen Pressure 11.Ion Implantation Doping and Isolation of III-Nitride Materials 12. High-Density ECR Etching of Group-III Nitrides 13. Contacts on III-Nitrides 14. III-V Nitride Based LEDs 15. III-V Nitride Electronic Devices 16. Physical Properties of the Bulk GaN Crystals Grown by the High-Pressure, High Temperature Method 17. Microstructure of Epitaxial III-V Nitride Thin Films 18. The Role of Hydrogen in GaN and Related Compounds

Chemical vapour deposition

Abstract: Chemical vapour deposition (CVD) is a powerful technology for producing high-quality solid thin films and coatings Although widely used in modern industries, it is continuously being developed as it is adapted to new materials Today, CVD synthesis is being pushed to new heights with the precise manufacturing of both inorganic thin films of 2D materials and high-purity polymeric thin films that can be conformally deposited on various substrates In this Primer, an overview of the CVD technique, including instrument construction, process control, material characterization and reproducibility issues, is provided By taking graphene, 2D transition metal dichalcogenides (TMDs) and polymeric thin films as typical examples, the best practices for experimentation involving substrate pretreatment, high-temperature growth and post-growth processes are presented Recent advances and scaling-up challenges are also highlighted By analysing current limitations and optimizations, we also provide insight into possible future directions for the method, including reactor design for high-throughput and low-temperature growth of thin films This Primer on chemical vapour deposition summarizes current and emerging experimental set-ups as well as common characterization approaches used to determine thin film formation and quality as applied to graphene and other novel 2D materials

Flexible and efficient perovskite quantum dot solar cells via hybrid interfacial architecture.

Abstract: All-inorganic CsPbI3 perovskite quantum dots have received substantial research interest for photovoltaic applications because of higher efficiency compared to solar cells using other quantum dots materials and the various exciting properties that perovskites have to offer These quantum dot devices also exhibit good mechanical stability amongst various thin-film photovoltaic technologies We demonstrate higher mechanical endurance of quantum dot films compared to bulk thin film and highlight the importance of further research on high-performance and flexible optoelectronic devices using nanoscale grains as an advantage Specifically, we develop a hybrid interfacial architecture consisting of CsPbI3 quantum dot/PCBM heterojunction, enabling an energy cascade for efficient charge transfer and mechanical adhesion The champion CsPbI3 quantum dot solar cell has an efficiency of 151% (stabilized power output of 1461%), which is among the highest report to date Building on this strategy, we further demonstrate a highest efficiency of 123% in flexible quantum dot photovoltaics

Defect Passivation in Lead-Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar cells

Abstract: Lead-halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next-generation, efficient light-emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge carriers into light and vice versa. However, despite the defect-tolerance of LHPs, defects at the surface of colloidal NCs and grain boundaries in thin films play a critical role in charge-carrier transport and nonradiative recombination, which lowers the PLQYs, device efficiency, and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes are critical for achieving advances in performance. This Review presents the current understanding of defects in halide perovskites and their influence on the optical and charge-carrier transport properties. Passivation strategies toward improving the efficiencies of perovskite-based LEDs and solar cells are also discussed.

Single-crystal hexagonal boron nitride monolayer epitaxially grown on Cu (111) thin film across a wafer

Abstract: We demonstrate single crystal growth of wafer-scale hexagonal boron nitride (hBN), an insulating atomic thin monolayer, on high-symmetry index surface plane Cu(111). The unidirectional epitaxial growth is guaranteed by large binding energy difference, ~0.23 eV, between A- and B-steps edges on Cu(111) docking with B6N7 clusters, confirmed by density functional theory calculations.

Room-temperature intrinsic ferromagnetism in epitaxial CrTe2 ultrathin films

Abstract: While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 $${\mu }_{{\rm{B}}}$$ /Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices. The emergence of two dimensional ferromagnetism suffers from an inherent fragility to thermal fluctuations, which typically restricts the Curie temperature to below room temperature. Here, Zhang et al present CrTe2 thin films grown via molecular beam epitaxy with a Curie temperature exceeding 300 K.

Tin Halide Perovskite Solar Cells: An Emerging Thin-Film Photovoltaic Technology

Abstract: ConspectusPerovskite semiconductors are regarded as next-generation photovoltaic materials owing to their superb optoelectronic properties, including an excellent carrier diffusion length, strong l...

Identifying the origin of the Voc deficit of kesterite solar cells from the two grain growth mechanisms induced by Sn2+ and Sn4+ precursors in DMSO solution

Abstract: Kesterite Cu2ZnSn(S,Se)4 solar cells fabricated from DMSO molecular solutions exhibit very different open circuit voltage (Voc) when the tin precursor has a different oxidation state (Sn2+vs. Sn4+). Here, the grain growth mechanism of the two absorbers was used as a platform to investigate the large voltage deficit issue that limits kesterite solar cell efficiency. The secondary sulfide composed Sn2+ precursor film took a multi-step phase fusion reaction path with secondary SnSe2 existing on the film surface during the whole grain growth, which forms in a very defective surface whereas a uniform kesterite structured Sn4+ precursor film took a direct transformation reaction path along with a top down and bottom up bi-direction grain growth that forms a uniform and less defective surface. Characterizations show that both absorber films exhibit similar bulk electronic properties with comparable band and potential fluctuations, Cu–Zn disorder level and tail states, and the much lower Voc of the Sn2+ device than the Sn4+ device primarily comes from the serious recombination near the junction as revealed by the large ideality factor and reverse saturation current. Our results demonstrate that the large Voc deficit of the kesterite solar cell mainly comes from surface deep defects that originated from the multi-phase fusion grain growth mechanism. The high efficiency (>12%) and low Voc deficit (<300 mV) of Sn4+ processed CZTSSe solar cells highlight that direct phase transformation grain growth is a new strategy to fabricate high quality kesterite absorbers, which can also be applied to other multi-element thin film semiconducting materials.

Atomic/molecular layer deposition for energy storage and conversion.

Abstract: Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this review, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

Supersaturation-Controlled Growth of Monolithically Integrated Lead-Free Halide Perovskite Single-Crystalline Thin Film for High-Sensitivity Photodetectors.

Abstract: Monolithical integration of the promising optoelectronic material with mature and inexpensive silicon circuitry contributes to simplifying device geometry, enhancing performance, and expanding new functionalities. Herein, a lead-free halide perovskite Cs3 Bi2 I9 single-crystalline thin film (SCTF), with thickness ranging from 900 nm to 4.1 µm and aspect ratio up to 1666, is directly integrated on various substrates including Si wafer, through a facile and low-temperature solution-processing method. The growth kinetics of the lead-free halide perovskite SCTF are elucidated by in situ observation, and the solution supersaturation is controlled to reduce the inverse-temperature crystallization nucleation density and elongate the evaporation growth. The excellent lattice match and band alignment between Si(111) and Cs3 Bi2 I9 (001) facets promote photogenerated charge dissociation and extraction, resulting in boosting the photoelectric sensitivity by 10-200 times compared with photodetectors based on other substrates. More importantly, this silicon-compatible perovskite SCTF photodetector exhibits a high switching ratio of 3000 and a fast response of 1.5 µs, which are higher than most reported state-of-the-art lead-free halide perovskite photodetectors. This work not only gives an in-depth understanding of the perovskite precursor solution chemistry, but also demonstrates the great potential of monolithical integration of lead-free halide perovskite SCTF with a silicon wafer for high-performance photodetectors.

Thin films of tungsten oxide materials for advanced gas sensors

Abstract: Thin film technology shows high promise in fabrication of electronic devices such as gas sensors. Tungsten trioxide (WO3), as one of the best-known metal oxide semiconductors (MOS) sensing materials, has attracted significant interest for application in gas sensors. In this review, WO3 thin films and their promising utilization as the sensing layers are overviewed to highlight their potential in gas sensors. First, the sensing mechanism for WO3 materials is briefly discussed. Then, several methods for WO3 film preparation are summarized. Following we discuss the specific gas sensing performances of WO3 film sensors to NO2, H2, NH3, and H2S. Strategies to improve the sensor properties such as sensitivity, response-recovery speed and selectivity are also discussed. Finally, the future perspectives and challenges of WO3 thin film sensors are addressed.

Wafer-scale heterostructured piezoelectric bio-organic thin films

Abstract: Piezoelectric biomaterials are intrinsically suitable for coupling mechanical and electrical energy in biological systems to achieve in vivo real-time sensing, actuation, and electricity generation. However, the inability to synthesize and align the piezoelectric phase at a large scale remains a roadblock toward practical applications. We present a wafer-scale approach to creating piezoelectric biomaterial thin films based on γ-glycine crystals. The thin film has a sandwich structure, where a crystalline glycine layer self-assembles and automatically aligns between two polyvinyl alcohol (PVA) thin films. The heterostructured glycine-PVA films exhibit piezoelectric coefficients of 5.3 picocoulombs per newton or 157.5 × 10-3 volt meters per newton and nearly an order of magnitude enhancement of the mechanical flexibility compared with pure glycine crystals. With its natural compatibility and degradability in physiological environments, glycine-PVA films may enable the development of transient implantable electromechanical devices.

Bright and stable light-emitting diodes made with perovskite nanocrystals stabilized in metal–organic frameworks

Abstract: Perovskite nanocrystals are exceptional candidates for light-emitting diodes (LEDs). However, they are unstable in the solid film and tend to degrade back to the bulk phase, which undermines their potential for LEDs. Here we demonstrate that perovskite nanocrystals stabilized in metal–organic framework (MOF) thin films make bright and stable LEDs. The perovskite nanocrystals in MOF thin films can maintain the photoluminescence and electroluminescence against continuous ultraviolet irradiation, heat and electrical stress. As revealed by optical and X-ray spectroscopy, the strong emission originates from localized carrier recombination. Bright LEDs made from perovskite-MOF nanocrystals are demonstrated with a maximum external quantum efficiency of over 15% and a high brightness of over 105 cd m−2 after the device reaches stabilization. During LED operation, the nanocrystals can be well preserved, free of ion migration or crystal merging through protection by the MOF matrix, leading to a stable performance over 50 hours. The use of metal–organic frameworks helps protect perovskite nanocrystals, resulting in bright, stable light-emitting diodes.

A magnetron sputtered Mo3Si thin film: an efficient electrocatalyst for N2 reduction under ambient conditions

Abstract: Industrially, large-scale NH3 production mainly depends on the Haber–Bosch process, which is accompanied by heavy greenhouse gas emission and serious energy consumption. Electrochemical N2 reduction is considered a sustainable strategy to solve this problem. Herein, we report for the first time that a Mo3Si thin film sputtered on graphite paper is a favorable electrocatalyst for NH3 synthesis under ambient conditions. Electrochemical tests suggest a large NH3 yield rate of 2 × 10−10 mol s−1 cm−2 and a high Faraday efficiency of 6.69% at −0.4 V and −0.3 V vs. a reversible hydrogen electrode, respectively, in 0.1 M Na2SO4. It also demonstrates the high electrochemical and structural stability of such a catalyst as well as excellent selectivity for NH3 generation. Density functional theory calculation reveals that the synergy of the metallic conductivity of Mo3Si and the high chemical activity of the exposed Mo ions benefits the adsorption and activation of N2, and a further proton–electron transfer reaction to produce NH3.

Efficient Wide-Bandgap Mixed-Cation and Mixed-Halide Perovskite Solar Cells by Vacuum Deposition.

Abstract: Vacuum deposition methods are increasingly applied to the preparation of perovskite films and devices, in view of the possibility to prepare multilayer structures at low temperature Vacuum-deposited, wide-bandgap solar cells based on mixed-cation and mixed-anion perovskites have been scarcely reported, due to the challenges associated with the multiple-source processing of perovskite thin films In this work, we describe a four-source vacuum deposition process to prepare wide-bandgap perovskites of the type FA1-n Cs n Pb(I1-x Br x )3 with a tunable bandgap and controlled morphology, using FAI, CsI, PbI2, and PbBr2 as the precursors The simultaneous sublimation of PbI2 and PbBr2 allows the relative Br/Cs content to be decoupled and controlled, resulting in homogeneous perovskite films with a bandgap in the 17-18 eV range and no detectable halide segregation Solar cells based on 175 eV bandgap perovskites show efficiency up to 168% and promising stability, maintaining 90% of the initial efficiency after 2 weeks of operation