Soft Deposition Research Articles

Soft Sputtering of Large-Area 2D MoS2 Layers Using Isolated Plasma Soft Deposition for Humidity Sensors.

2D transition-metal dichalcogenides are emerging as key materials for next-generation semiconductor technologies owing to their tunable bandgaps, high carrier mobilities, and exceptional surface-to-volume ratios. Among them, molybdenum disulfide (MoS2) has garnered significant attention. However, scalable wafer-level deposition methods that enable uniform layer-controlled synthesis remain a critical challenge. In this paper, a novel fabrication approach-isolated plasma soft deposition (IPSD) followed by sulfurization-for the scalable production of 2D MoS2 with precise layer control is introduced. The IPSD system employs a scanning-based deposition method combined with plasma surface pretreatment, achieving large-area, high-quality 2D MoS2 layers. Comprehensive characterizations using Raman, UV-vis, and photoluminescence spectroscopy, and transmission electron microscopy confirmed the successful synthesis of crystalline mono- to tetralayer 2D MoS2 on 6-inch SiO2/Si substrates. Furthermore, respiration sensors fabricated using the IPSD-grown 2D MoS2 layers demonstrated fast response times (≈1 s) and high response to relative humidity levels between 30% and 60%. This study offers significant advancements in the scalable synthesis of 2D MoS2 and opens new avenues for its application in advanced sensing and electronic devices.

Soft deposition of TCOs by pulsed laser for high-quality ultra-thin poly-Si passivating contacts

In this work, the applicability of pulsed laser deposition (PLD) of transparent conductive oxides (TCOs) on high-quality ultra-thin poly-Si based passivating contacts is explored. Parasitic absorption caused by poly-Si layers can be minimized by reducing the poly-Si layer thickness. However, TCO deposition on poly-Si contacts, commonly by sputtering, results in severe deposition-induced damage and further aggravates the surface passivation for thinner poly-Si layers (<20 nm). Although a thermal treatment at elevated temperature (∼350 °C) can be used to partially repair the surface passivation quality, the contact resistivity severely increases due to the formation of a parasitic oxide layer at the poly-Si/ITO interface. Alternatively, we show that PLD TCOs can be used to mitigate the damage on ultra-thin (∼10 nm) poly-Si layers. Further improvement in poly-Si contact passivation can be achieved by increasing the deposition pressure while low contact resistivities (∼45 mΩ cm2) and good thermal stability (up to 350 °C) are achieved with a PLD indium-doped tin oxide (ITO) layer on high-quality ultra-thin poly-Si(n+) contacts. This allows for the application of a highly transparent front side contact by combining the excellent opto-electrical properties of a PLD ITO film with a 10 nm thin poly-Si contact.

Soft Deposition of Organic Molecules Based on Cluster-Induced Desorption for the Investigation of On-Surface and Surface-Mediated Reactions.

Desorption/ionization induced by neutral clusters (DINeC) was employed for the soft transfer of organic and biomolecules, such as porphyrins and peptides, from a bulk sample onto any substrate of choice. Qualitative analysis of the deposition technique was performed by means of mass spectrometry, demonstrating that the deposited molecules remained intact due to the soft nature of the transfer process. Deposition rates were studied quantitatively using a quartz crystal microbalance; layers of intact biomolecules ranging from the submonolayer regime up to a few monolayers in thickness were realized. Mixed layers of molecules were deposited when two different sources of molecules were employed. The samples which were prepared based on this soft deposition method were used for the investigation of reactions of the deposited molecules with either coadsorbates on the surface or the surface itself. Examples include adduct formation of peptides with alkali metals on SiO2, the oxidation of peptides exposed to oxygen, as well as the metallization of porphyrins in interaction with the substrate.

Indigenous facility of the unipolar pulsed power generation for gas flow sputtering of titania films

Gas flow sputtering is a sputter deposition method that enables soft and high-rate deposition even for oxides or nitrides at high pressure (in the mbar range). A unipolar pulse generator with adjustable reverse voltage was used to optimize thin film growth by the hollow cathode gas flow sputtering system. In this regard, we describe our laboratory Gas Flow Sputtering (GFS) deposition system, which has been recently assembled at the Technical University of Berlin. Its technical facilities and suitability for various technological tasks are explored. The first experimental efforts are presented by the example of TiOx films on glass substrates obtained at various deposition conditions with forced Argon flow. The influence of pulsing parameters, power, and oxygen gas flow on the plasma generated is studied. The films were characterized by ellipsometry, scanning electron microscopy, x-ray diffraction, and x-ray reflectivity. Optical Emission Spectroscopy (OES) was also used to characterize the remote plasma, and the substrate temperature was measured. The pulsing frequency (f) is a significant factor that provides additional substrate heating by about 100 °C when the plasma regime changes from f = 0 (DC) to 100 kHz. Such a change in frequency provides a significant increase in the OES signals of Ti and Ar neutrals as well as of Ti+ ions. With pulsed operation at high power, the GFS plasma is capable of heating the glass substrate to more than 400 °C within several minutes, which allows for crystalline anatase TiOx film deposition without external heating. For deposition below 200 °C substrate temperature, low power DC operation can be used.

Plasma damage-free deposition of transparent Sn-doped In2O3 top cathode using isolated plasma soft deposition for perovskite solar cells

We developed an isolated plasma soft deposition (IPSD) technique for the plasma damage-free deposition of a Sn-doped In2O3 (ITO) top cathode on semi-transparent perovskite solar cells (PSCs). Unlike the directly faced plasma in conventional magnetron sputtering, the isolated plasma region in the IPSD process prevents the direct irradiation of plasma and facilitates plasma damage-free sputtering. Effective confinement of high-density plasma in isolated regions by using a specific Nd-Fe-B45 magnet array also prevents irradiation of energetic particles sputtered from faced ITO targets. In addition, linear scanning of the substrate in the isolated plasma region resulted in a low-temperature and large-area coating of the ITO top cathode without plasma damage for semi-transparent PSCs. Without intentional substrate heating, the IPSD-processed ITO film with a thickness of 100 nm under optimal conditions exhibited a low sheet resistance of 33.02 Ohm/square, high optical transmittance of 91.27%, root mean square roughness of 0.252 nm, and work function of 4.33 eV. To demonstrate the feasibility of IPSD, we fabricated PSCs with thermally evaporated perovskite active layers. Compared with the power conversion efficiency (PCE: 4.35%) of PSCs with magnetron-sputtered ITO cathode, the PSC with IPSD-processed ITO cathode exhibited a similar PCE (15.52%) because of the absence of plasma damage. Considering the commercialization of PSCs, the IPSD-based top cathode coating process possesses great potential as a key technique for bidirectional or semi-transparent PSCs.

Evaluation of Soft Mist Inhaler Aerosol Velocity, Size, and Deposition Inside the Mouth-A Computational Fluid Dynamics Study.

Respiratory diseases debilitate more than 250 million people around the world. Among available inhalation devices, the soft mist inhaler (SMI) is the most efficient at delivering drugs to ease respiratory disease symptoms. In this study, we analyzed the SMI performance in terms of the aerosol's velocity profiles, flow pattern, size distribution, and deposition by employing computational fluid dynamics (CFD) simulations. We modeled two different simplified mouth geometries, idealized mouth (IM), and standard mouth (SM). Three different locations (x = 0, x = 5, and x = 10 mm) for the SMI nozzle orifice were chosen along the mouth cavity centerlines, followed by two different SMI nozzle angles (10 deg and 20 deg) for IM geometry. A flowrate of 30 L/min was applied. The simulation results were evaluated against experimental data. It was found that the SMI could be simulated successfully with a level of error of less than 10%. The inhalation flowrate significantly impacted the aerosol's velocity profile and deposition efficiency on both the IM and SM walls. The lowest particle deposition on the mouth wall occurred when a fixed flowrate (30 L/min) was applied inside both geometries, and the SMI nozzle position moved forward to x = 10 mm from the IM and SM inlets. An increase in the SMI nozzle angle increased particle deposition and decreased the deposition fraction for particles with a diameter above 5 μm inside the IM.

Scratch adhesion evaluation of diamond like carbon coatings with alternate hard and soft multilayers

A series of four diamond like carbon coatings comprising alternating soft and hard layers was prepared by closed field unbalanced magnetron sputtering. A constant bias voltage of −40 V was used for soft layer deposition, while the hard layers were deposited at different bias voltages for different coatings in series. A uniform hard-to-soft layer thickness ratio of approximately 1:1.33 was maintained for all four coatings. Cross-sectional transmission electron microscopy of the coatings confirmed that these diamond like carbon coatings indeed exhibited distinct soft and hard layers. Moreover, increasing bias voltage during hard layer deposition also increased the residual stress in these coatings. The coatings were also subjected to scratch testing to determine the effect of increasing bias voltage on the scratch toughness. Scratch cracking mechanism changed from chevron tensile cracking at low bias voltages to buckle spallation at higher bias voltages. All the coatings exhibited substrate exposure at high normal loads beyond the upper critical load. The scratch crack propagation resistance parameter was reduced by ∼1.5 times when the bias voltage was increased to −140 V. It was demonstrated that coatings deposited at a hard layer bias voltage of −100 V demonstrated the best combination of mechanical properties, including the plastic deformation resistance (H3/E2 ratio) and elastic strain to failure (H/E ratio).

Stability of Cu2ZnSnSe4/CdS heterojunction based solar cells under soft post-deposition thermal treatments

The thermal stability of the Cu 2 ZnSnSe 4 (CZTSe) absorber and CdS buffer layers in SLG/Mo/CZTSe/CdS/i-ZnO/ITO devices is explored by performing a series of soft (∼200 °C) post deposition treatments (PDTs). A comprehensive analysis of a sample comprised by 56 individual devices by means of Raman and photoluminescence spectroscopies coupled with optoelectronic characterization is performed at different PDT steps. This allows isolating the effects of the PDT on the CZTSe absorber and CdS buffer layer separately and reveals clear evidences of: i) a degradation of the absorber due to Cu/Zn disorder that hinders device performance, and ii) an improvement of the buffer layer by the recrystallization of the CdS nanolayer that is the main responsible for the PDT-induced efficiency improvement. As such, it is concluded that CZTSe/CdS based PV devices present a low thermal stability under relatively low temperatures (in the 100–200 °C range), comparable to the temperatures employed at the final production stages of thin film PV devices or even during device operation, that leads to significant changes in solar cell performance and needs to be taken into consideration for the further development of the kesterite PV technology. These results are supported by a novel methodology for easily discerning between changes in Cu/Zn disorder and in point defects concentration in kesterites based on solely on Raman spectroscopy that is proposed in this work and developed through the analysis of a set of CZTSe powder samples with strong variation of the order parameter Q. • The CZTSe/CdS heterojunction is unstable under soft post deposition treatment (PDT). • Soft PDT induced performance improvement arises from a recrystallization of the CdS. • Soft PDT induces detrimental Cu/Zn disorder at the CZTSSe absorber layer. • Raman spectroscopy can discern between changes in disorder and defect concentration.

Dielectric behavior of curcuminoid polymorphs on different substrates by direct soft vacuum deposition.

Our work examines the structural-electronic correlation of a new curcuminoid, AlkCCMoid, as a dielectric material on different substrates. For this purpose, we show a homemade sublimation method that allows the direct deposition of molecules on any type of matrix. The electronic properties of AlkCCMoid have been evaluated by measurements on single crystals, microcrystalline powder, and sublimated samples, respectively. GIWAXS studies on surfaces and XRD studies on powder have revealed the existence of polymorphs and the effect that substrates have on curcuminoid organization. We describe the dielectric nature of our system and identify how different polymorphs can affect electronic parameters such as permittivity, all corroborated by DFT calculations.

Effective synthesis of limonene over mild alkali-modified 13X catalysts in α-pinene isomerization

The mild alkali-treated 13X was employed in the liquid phase isomerization reaction of α-pinene to increase the yield of limonene. A maximum α-pinene conversion of 100% and limonene yield of 59.1% could be achieved. Crystallinity could be well retained, and the amounts of medium-strong acid sites and the distribution of Brønsted and Lewis acid sites could be changed after the mild alkali treatment for 13X zeolite. Samples with higher micropore specific surface area were easier to obtain higher yields of limonene due to shape-selectivity. A proper amount of the medium-strong acid and the synergistic effect of Brønsted and Lewis acid sites were beneficial to enhance the catalytic activity and the yield of monocyclic product limonene. The main reason for catalyst deactivation could be the decrease in the active sites due to soft coke deposition. For the regeneration process, the conversions of α-pinene were between 95% and 99% during the first seven cycles and the conversion dropped to 90.6% after the eighth cycle, which demonstrated that the ethanol flushing and calcination could be an effective regeneration method for the 13X catalyst used in the α-pinene isomerization reaction.

Simulation analysis of Cd-free Cu(In,Ga)Se2 solar cells with novel BiOX (X=Cl, Br) buffer layers

Nowadays, cadmium sulfide (CdS) or zinc oxysulfide (Zn(O,S)) are the traditional buffer layer of Cu(In,Ga)Se2 (CIGS) solar cells. However, these buffer layers contain several disadvantages, such as the complicated synthesis problem and heavy metal toxicity. To solve the above problems, the potential of Bi-based (BiOX: X = Cl, Br) materials employed as buffer layers for efficient CIGS solar cells are investigated by using SCAPS simulation software in this contribution. It can be found that all BiOX materials fabricated from a soft liquid deposition process possess 2D nanosheet structures. A comparison of 2D nanosheet size reveals that BiOBr can form easily compared with BiOCl under the same growth conditions. Simultaneously, DRS and XPS determine the energy band distribution of BiOX materials. Further investigations on the simulated device performance suggest that conversion efficiency of the BiOBr sample is maximum, which is close to that of CdS and much larger than the BiOCl sample, mostly owning to the increased JSC and FF. The reason for this results is that the energy band distribution of BiOBr is similar to that of CdS buffer layer. It also indicates that BiOBr has the potential to serve as a buffer layer material for solar cells.

A novel soft deposition methodology for textured ZnO:Al thin films as efficient transparent conductive oxide layers

In this paper, a novel soft deposition methodology was developed for depositing Al-doped ZnO (AZO) thin films as Transparent Conducting Oxide (TCO) layer. The new proposed methodology could help in reducing the process time and cost that could subsequently be useful for industrial scalability purposes. In general, the effect of substrate distance (dTS), Ar gas flow (FAr), and sputtering power (PW) were analyzed on structural, morphological, optical, and electrical properties. Films exhibiting the best electrical values (3.2 × 10−4 Ω*cm, 21.3 cm2 V−1 s−1, and 9.2 × 1020 cm−3) were deposited at FAr of 5 sccm, PW of 45 W, and room temperature. Additionally, AZO thin films deposited inside the high-density zone (HDZ, dTS < 6 cm) of the plasma sputtering exhibited a textured surface with crater-like morphology, and it was found to be more evident in films deposited at reduced FAr (5 sccm) and low PW (45 W) values. The present methodology could be of great interest for the low-cost production of AZO thin films with a textured surface obtained in a one-step DC sputtering process for modern optoelectronic applications such as flexible solar cells and electroluminescent devices.

Determination of a quantitative relationship between deposition duration and magnetic performance of soft ferromagnetic composites via data-analysis and theoretical models

The industrial production of soft ferromagnetic composites demands a quantitative description of process parameters and magnetic performance. Here, Fe–Si/SiO2 soft ferromagnetic composites were prepared via a two-step method combining chemical vapour deposition and hot-pressed sintering. Investigations of surface and section morphology, phase composition and crystal structure were undertaken to characterise the deposition duration-dependence of SiO2 insulation coating thickness in Fe–Si/SiO2 soft ferromagnetic composites. A vibrating sample magnetometer, a resistivity tester and a B–H analyser were used to study the magnetic behaviours of Fe–Si/SiO2 soft ferromagnetic composites. Based on curves of deposition duration-dependence of SiO2 insulation coating thickness and other theoretical models, quantitative relationships between deposition duration and magnetic performance were determined for Fe–Si/SiO2 soft ferromagnetic composites. These results demonstrate that the coating and crystallisation of SiO2 insulation coatings had no influence on the crystal structure of Fe–Si substrate particles and that SiO2 insulation coating thickness increased linearly with deposition duration. Total core loss of Fe–Si/SiO2 soft ferromagnetic composites was strongly predicted by SiO2 insulation coating thickness. A quantitative equation relating magnetisation intensity to Fe–Si/SiO2 soft ferromagnetic composite deposition duration was derived on the basis of experimental data and subsequent model selection. Additional quantitative equations relating electrical resistivity and eddy current loss to Fe–Si/SiO2 soft ferromagnetic composite deposition duration were determined according to electromagnetic theory. These results establish a precise adjustment mechanism for magnetic behaviour in Fe–Si/SiO2 soft ferromagnetic composites and promote the industrialisation of a new preparation process combining chemical vapour deposition and hot-pressed sintering.

Mechanical, Electrochemical, and Osteoblastic Properties of Gradient Tantalum Coatings on Ti6Al4V by Prepared Plasma Alloying Technique

Plasma alloying technique capable of producing metallic coatings with metallurgical bonding has attracted much attention in dental and orthopedic fields. In this study, the effects of temperature and time of plasma tantalum (Ta) alloying technique on the mechanical, electrochemical, and osteoblastic properties of Ta coatings were systematically investigated. Ta coatings prepared at 800 °C possess better interfacial strengths than those prepared at 750 and 850 °C, and the interfacial strength increases with prolonged alloying time (30–120 min). At 800 °C, however, the increased proportion of the soft Ta deposition layer with alloying time in the whole coating impairs the surface mechanical properties of the entire coating, as convinced by decreased microhardness and wear resistance. Moreover, Ta coatings exhibit better corrosion resistance than the Ti6Al4V substrate in Dulbecco’s modified Eagle medium. The enhanced adhesion and extracellular matrix mineralization level of osteoblasts demonstrate the better cytocompatibility and osteogenic activity of the Ta coating. Ta30 (Ta coating prepared at 800 °C for 30 min) exhibits excellent mechanical, electrochemical, and osteoblastic behaviors and is promising in biomedical applications.

Seismic Performance Assessment of Velocity Pulse-Like Ground Motions Under Near-Field Earthquakes

As a part of the earthquake ground motion, large velocity pulses are probably one of the important factors leading to serious rock structural damage and geological disasters. It is vitally important to identify the response characteristics of large-scale structures under near-field pulse-like ground motions for earthquake prevention and disaster reduction. In this study, the pulse parameters from the 1999 Chi-Chi and 2018 Hualien earthquakes are extracted using the wavelet transform method, and the potential consequences of velocity pulses on the seismic response of the buildings are assessed. Our results show that the near-field ground motions affected by the directivity effect contain some rich large pulse contents in the velocity time histories. The Chi-Chi earthquake presents a more obvious directivity effect than the Hualien earthquake, and the near-field velocity pulses are closely related to the severely damaged structures. The potential damage of both earthquakes to high-rise buildings can be evaluated by the relationship between the characteristic period of the velocity pulse and the fundamental natural period of the engineering structure. By comparing the periods, it can be revealed that some long-period spectral values in the range of 0.8–3.0 s exceed the seismic design values in the vicinity of the causative faults, and the vulnerability of high-rise buildings against pulse-like ground motions in the Chi-Chi earthquake is stronger than that in the Hualien earthquake. Interestingly, the ratio of peak ground velocity to acceleration (PGV/PGA) and maximum pseudo response velocity (PSV) are suitable as seismic intensity indicators of pulse-like ground motions, which can reflect the rupture direction of source characteristic and site amplification of near-surface soft deposition area around the causative fault. This study provides some references for seismic hazard assessment and post-earthquake structural design.

Hyperparathyroidism Tumoral calcinosis: A case report

Tumoral calcinosis (TC) is a rare locally aggressive lesion characterised by extra-articular soft tissue deposition of the calcium phosphate around large joints & small joints. The exact aetiology is not known. A 11–year–old female presented with a painful progressive swelling around the medial aspect of 1st metatarsal right foot over a 6–month duration. Routine laboratory results showed a normal haemogram, and normal calcium and high phosphate levels & para thyroid level. Imaging showed a soft tissue calcified mass around 1st metatarsal medial aspect of right foot. The cut surface of the excised mass showed myxoid material with areas of calcification. On microscopy, there were typical features of Tumoral calcinosis.

Particle temperature effect in cold spray: A study of soft particle deposition on hard substrate

In cold spray, the interactions between feedstock particles and propellant gas control deposition outcome. The particle impact temperature, along with impact velocity, governs the deposition due to its effect on the impact deformation processes. As bonding mechanisms rely primarily on the particle/substrate plastic flow upon impact, particle impact temperature holds a predominant role in process optimization.The current work studies the effect of pure aluminum particle impact temperature on deposition phenomena when propelled onto a hard steel substrate. Particle impact temperature was varied while achieving the same particle impact velocity, using low and high-pressure cold spray systems. Three different particle diameters are studied, with varying resulting inherent impact temperatures, to provide size dependent insight on deposition/adhesion.Experimental results demonstrate that at low particle impact temperature, i.e. 50 °C, coating adhesion is controlled by in-situ peening. Adhesion shifts to particle in-flight characteristics dependent bonding, i.e. η = V/Vc, as particle temperature increases. At low particle impact temperatures, the coating bond strength increases with increasing in-situ impingement intensity and frequency, i.e. decreasing deposition efficiency with increasing particle size. At higher particle impact temperatures, in-situ peening rate decreases and the adhesion strength increases with decreasing particle size. In addition to affecting the impact process (DE, Vc and adhesion), the particle impact temperature also influences the coating mechanical properties through the creation of temperature-dependent crack propagation mechanisms, i.e. deflection, bridging and acceleration, and of particle-particle structural arrangement related to deformation processes, i.e. fish scale effect and pseudo-plasticity behavior.

290 Phosphorus and calcium requirements of growing pigs predicted by mechanistic modelling

Abstract Phosphorus (P) is a key element for the sustainability of pork production systems. The response of pigs to P intake is complex and optimize P utilization requires a multicriteria approach. A mechanistic mathematical model representing the P and Ca absorption and bone and soft tissues deposition was developed and used to optimize these minerals utilization. Model P and Ca requirements (g/kg) were also compared to those of INRA (Jondreville and Dourmad, 2005; apparent total tract digestible P, ATTD-P) and NRC (2012; standardized total tract digestible P, STTD-P) requirements in different bone mineralisation scenarios (100 and 85%). The proposed model showed lower ATTD-P and STTD-P requirements than INRA (6%) and NRC (7%), between 29 to about 98 kg of body weight (BW) and higher (up to 17%) at other weights. The proposed model Ca requirements increase after 95 kg BW unlike NRC and INRA Ca requirements that decrease. For 100 % of bone mineralisation, INRA show the highest Ca requirements (21%) while NRC requirements are similar between 35 to 65 kg and the model requirements are higher for other weights. For 85% objective, the model showed lower Ca requirements than NRC from 25 to 82 kg of BW (9%). The Ca:ATTD-P ratio increased curvilinearly with BW varying from 2.2 to 2.6. The differences observed with the current model and NRC and INRA are due to the structure of the model, that simulates the bone independently of the protein, the first evolving linearly with the weight while the second follows a Gompertz function. Therefore a non-fixed Ca:ATTD-P (or STTD-P) ratio could be consider to maximize bone mineralisation. By predicting bone and muscle growth independently the model offers greater allometric insight into nutrient requirements and their interactions. Studies such as this one will help to usher in a new era of sustainable and eco-friendly livestock production.

Role of nutritional history in the attachment and retention of green-lipped mussel spat

The global mussel aquaculture industry relies heavily on the use of wild seed mussels or spat to initiate aquaculture production. However, production efficiency is often compromised by the poor performance of spat following seeding onto aquaculture substrates such as grow ropes. A potential cause of poor performance of spat is compromised nutritional condition that can be associated with poor natural feeding conditions for wild spat immediately prior to harvest, as well as their subsequent inappropriate handling until seeding into aquaculture infrastructure. This study examines the importance of nutritional condition of spat to their subsequent attachment and retention after seeding into mussel aquaculture. Spat of the green-lipped mussel, Perna canaliculus, were experimentally starved for 0, 3, 6 and 9 days before being seeded into suspended culture in a coastal mussel farm. At the end of the laboratory starvation phase of the experiment the attachment, growth, soft tissue deposition and energy reserves (total carbohydrate content) of spat all tended to decrease with increasing starvation treatment. Fourteen days after seeding the spat to a mussel farm, there was a further general decrease in all of the observed variables in spat from their initial state at seeding out. The results suggests that after seeding to the mussel farm, the spat were subject to poor local feeding and environmental conditions and that conditions at mussel farms at the time of seeding spat may play an important role in determining early spat performance. While providing a short period of feeding for spat prior to seeding onto mussel farms will improve their immediate nutritional condition, growth and attachment, the subsequent performance of spat after seeding onto farms may be more dependent on ensuring favourable conditions at the farm site.

Strong performance enhancement in lead-halide perovskite solar cells through rapid, atmospheric deposition of n-type buffer layer oxides

Thin (approximately 10 nm) oxide buffer layers grown over lead-halide perovskite device stacks are critical for protecting the perovskite against mechanical and environmental damage. However, the limited perovskite stability restricts the processing methods and temperatures (<=110 C) that can be used to deposit the oxide overlayers, with the latter limiting the electronic properties of the oxides achievable. In this work, we demonstrate an alternative to existing methods that can grow pinhole-free TiOx (x = 2.00+/-0.05) films with the requisite thickness in <1 min without vacuum. This technique is atmospheric pressure chemical vapor deposition (AP-CVD). The rapid but soft deposition enables growth temperatures of >=180 {\deg}C to be used to coat the perovskite. This is >=70 {\deg}C higher than achievable by current methods and results in more conductive TiOx films, boosting solar cell efficiencies by >2%. Likewise, when AP-CVD SnOx (x ~ 2) is grown on perovskites, there is also minimal damage to the perovskite beneath. The SnOx layer is pinhole-free and conformal, which reduces shunting in devices, and increases steady-state efficiencies from 16.5% (no SnOx) to 19.4% (60 nm SnOx), with fill factors reaching 84%. This work shows AP-CVD to be a versatile technique for growing oxides on thermally-sensitive materials.