Large-grained Films Research Articles

Thermal-triggered healing strategy for efficient and stable perovskite solar cells with efficiency over 25 %

The power conversion efficiency (PCE) of organic-inorganic hybrid perovskite solar cells (PSCs) is hindered by the abundant defects within the grain boundaries (GBs) of perovskite films. Herein, a directed thermal-triggered healing strategy based on phthalide-3-acetic acid (P3AC) is proposed, aiming to mitigate GBs defects and optimize energy level arrangement by utilizing the strong polarity effect of P3AC and its thermal-triggered interaction with perovskite. The introduced dual-sites molecular (P3AC) anchors at the GBs of perovskite, which can passivate the uncoordinated Pb2+ and form hydrogen bonds with FA+, yielding dense, uniform and low-defects and large-grain perovskite film. Compared to the pristine devices, the P3AC-modified devices achieved a champion PCE of 25.28 % (certified PCE of 24.46 %) and impressive operational stability. This work provides an effective and direct solution for enhancing the performance of PSCs.

Simultaneously Enhancing the Efficiency and Stability of Perovskite Solar Cells by Using P3HT/PEDOT:PSS as a Double Hole Transport Layer.

The stability issue of perovskite solar cells (PSCs) has long been of concern to researchers. Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is commonly used as a hole transport layer (HTL) in the inverted PSCs to achieve efficient and stable performance. However, PEDOT:PSS can corrode ITO, affecting device efficiency. Moreover, the hydrophilic nature of PEDOT:PSS compromises device stability. In this work, Poly (3-hexylthiophene-2,5-diyl) (P3HT), known for its good hydrophobicity, was used to modify the surface of PEDOT:PSS, reducing its water absorption and thereby enhancing the efficiency and stability of PSCs. The results reveal that incorporating P3HT effectively enhances the hydrophobicity of PEDOT:PSS. Furthermore, it fosters the development of large-grain perovskite film on the PEDOT:PSS/P3HT bilayer. This enhancement leads to a power conversion efficiency (PCE) of 19.78% for PSCs, with an increase by 16% than that of reference cells (17.04% of PCE). Following a duration of 1000 h, the PCE for the device modified with P3HT remains above 90%, while the PCE of the reference device is below 70%. These findings suggest that using P3HT in conjunction with PEDOT:PSS as a bilayer HTL can concurrently and proficiently improve the efficiency and stability of PSCs.

A novel Se-diffused selenization strategy to suppress bulk and interfacial defects in Sb2Se3 thin film solar cell

In recent years, vacuum-based deposition of antimony selenide (Sb2Se3) thin films has garnered significant attention owing to its easy and impurity-free fabrication, along with exceptional power conversion efficiency (PCE). However, the necessary post-selenization process comes with a shortcoming of instigating buried Sb2Se3/molybdenum (Mo) back-contact interface defects. This study introduces a novel Se-diffusion post-selenization technique to precisely regulate the selenium reaction atmosphere, preventing void formation on the Sb2Se3 thin film surface and maintaining film quality for enhanced device efficiency. An optimized selenization condition with a precise Se precursor film thickness led to obtaining highly crystalline, preferentially (hk1) oriented, and large-grained Sb2Se3 films. Furthermore, a meticulous Se diffusion in Sb2Se3 film reduced the inevitable MoSe2 layer thickness at the Mo surface, thereby enhancing the quality of the back contact interface. The Sb2Se3 solar cell that was selenized to optimal level showed significant enhancements, raising the fill factor from 40.06 % to 45.12 % and improving the device efficiency from 2.89 % to 3.57 %. Our newly developed selenization strategy establishes a successful approach to regulate the Sb2Se3 film quality by addressing a crucial challenge in improving the efficiency of antimony chalcogenide solar cells.

Low-Temperature Deposition of Diamond Films by MPCVD with Graphite Paste Additive

Modern integrated circuits (ICs) take advantage of three-dimensional (3D) nanostructures in devices and interconnects to achieve high-speed and ultra-low-power performance. The choice of electrical insulation materials with excellent dielectric strength, electrical resistivity, strong mechanical strength, and high thermal conductivity becomes critical. Diamond possesses these properties and is recently recognized as a promising dielectric material for the fabrication of advanced ICs, which are sensitive to detrimental high-temperature processes. Therefore, a high-rate low-temperature deposition technique for large-grain, high-quality diamond films of the thickness of a few tens to a few hundred nanometers is desirable. The diamond growth rate by microwave plasma chemical vapor deposition (MPCVD) decreases rapidly with lowering substrate temperature. In addition, the thermal conductivity of non-diamond carbon is much lower than that of diamond. Furthermore, a small-grain diamond film suffers from poor thermal conductivity due to frequent phonon scattering at grain boundaries. This paper reports a novel MPCVD process aiming at high growth rate, large grain size, and high sp3/sp2 ratio for diamond films deposited on silicon. Graphite paste containing nanoscale graphite and oxy-hydrocarbon binder and solvent vaporizes and mixes with gas feeds of hydrogen, methane, and carbon dioxide to form plasma. Rapid diamond growth of diamond seeds at 450 °C by the plasma results in large-grained diamond films on silicon at a high deposition rate of 200 nm/h.

Fabrication of phase-pure and large-grained Cu3BiS3 films by a two-stage process for thin film solar cells

Copper-bismuth-sulfide (Cu3BiS3) has gained great interest as solar cell absorber owing to the advantages of being cheap, abundant, and non-toxic. Fabrication of phase-pure and large-grain absorbers are desirable for their integration in solar cells. Herein, we have used a sequential evaporation and chalcogenization (350–450 oC) process to fabricate phase-pure and large-grain Cu3BiS3 films. X-ray diffraction indicated a CuS secondary phase at 350 °C and single-phase Cu3BiS3 at 400 and 450 °C in the sulfurized films. Elemental analysis revealed a near-stoichiometric Cu3BiS3 composition for all the films. X-ray photoelectron spectroscopy was used to assess the valence states of elements. Microstructural analysis confirmed the formation of compact and large-grained Cu3BiS3 films with an average grain size of 5 μm at 350 °C. The grain size decreased with increasing sulfurization temperature (400–450 °C). The direct bandgap decreases from 1.42 eV to 1.32 eV with increasing sulfurization temperature from 350 to 450 °C. Hall measurements indicated decreased electrical resistivity and increased hole mobility and carrier concentration with increasing the sulfurization temperature. From this study, the Cu3BiS3 absorbers produced at 400 oC exhibited superior phase purity and good quality suitable for the solar cells.

Microstructural, electrical, and optoelectronic properties of BaSi2 epitaxial films grown on Si substrates by close-spaced evaporation

BaSi2, an earth-abundant photovoltaic material with a limiting efficiency of 32 %, has the interesting property that grain boundaries do not significantly degrade the film properties. In this study, we investigated the microstructure and its effect on the electrical and optoelectronic properties of the BaSi2 films grown by close-spaced evaporation. Microstructural analysis confirmed the (100)-oriented epitaxial growth on both Si(100) and Si(111) substrates. In addition to conventional epitaxial relationships, lattice matching with the BaSi2(01¯3) plane parallel to Si(110) was observed on Si(100) substrates. The density of the epitaxial domain boundary was found to decrease with increasing film thickness, increasing growth temperature, and using Si(100) substrates instead of Si(111). Hall effect measurements revealed the conductivity type transition at a temperature between 900 and 1000 ∘C and a decreasing tendency of carrier density with film thickness. There was no obvious correlation between mobility and grain boundary density, consistent with previous reports. Carrier recombination kinetics were evaluated by the microwave-detected photoconductivity decay method and the photoconductivity measurement under constant optical irradiation. Both analyses revealed weak negative correlations between excess carrier lifetime and grain boundary density, which clarified the superiority of large-grained BaSi2 films for photovoltaic applications.

Highly strained and heavily doped germanium thin films by non-equilibrium high-speed CW laser annealing for optoelectronic applications

The integration of light transmitters into electronic circuits is essential for the development of optical communication systems. A direct bandgap semiconductor with excellent electrical properties is preferable for a cost-effective and high-performance device. Germanium is considered a promising candidate for CMOS-compatible optoelectronics, even though the light emission is inefficient due to its indirect bandgap property. It has been reported that applying tensile strain modifies the energy band structure thus making quasi-direct bandgap emission possible. In addition, n-type doping has been expected to improve this emission. We have realized high tensile strain in polycrystalline germanium grown on a quartz substrate by employing continuous wave laser annealing (CWLA). In this study, we investigated the implementation of a similar annealing technique with antimony doped samples to combine both tensile strain and n-type doping in a Ge-on-insulator (GeOI) structure. We investigated various samples with different interfaces to achieve large-grained polycrystalline films on insulator. Characterizations of the CWLA processed samples revealed the successful introduction of both tensile strain and n-type doping in GeOI. The properties were confirmed by the enhancement of direct Γ-LH emission that observed even for room-temperature optical measurements. These results provide an important insight that will assist the feasible and large-scale development of germanium-based optoelectronic devices.

Combined effects of residual stress and microstructure on degradation of Cu thin films on Si

In this paper, combined effects of residual stress and microstructure on degradation of Cu thin films on Si have been investigated. Magnetron sputtering with different processing parameters produced cracked and non-cracked Cu films with various grain sizes and residual stresses. Phase transformation and the change in electrical resistance of the Cu thin films have been analyzed for different annealing conditions. It has been revealed that non-cracked and large-grained (25.2±8.9nm) Cu films with high tensile residual stress (186 MPa) result in the most significant degradation (sheet resistance increase of 894%) upon annealing at 300°C. Specimens with smaller grains (17.3±6.4 nm) and low residual stress (41.6 MPa) or cracks showed no increase in sheet resistance after annealing at 300°C. The microstructural evaluation showed that residual stress of Cu affects the grain growth rate during annealing, which is closely related to the Cu/Si interdiffusion behavior.

Metal-organic frameworks with mixed-ligands strategy as heterogeneous nucleation center to assist crystallization for efficient and stable perovskite solar cells

Deep-level defects and random oriented configuration in perovskite crystallization process would cause the nonradiative recombination and further affect the performance of perovskite solar cells (PSCs). Herein, two metal-organic frameworks (MOFs) with tunable Lewis-base passivation sites have been constructed (Cd-Httb and Cd-Httb-BDC, Httb = 5-(4-(1H-1,2,4-triazole-1-yl)benzyl)-1h-tetrazole, BDC = 1,4-dicarboxybenzene) to eliminate deep-level defects and simultaneously as nanostructured heterogeneous nucleation seed to assist the growth of large-grained perovskite films. Compared with the control and Cd-Httb, Cd-Httb-BDC designed with mix-ligands strategy exhibited the enhanced inducted effect on the crystallization and nucleation of high-quality perovskite films during annealing process. Consequently, the resultant Cd-Httb-BDC-modified device achieved higher power conversion efficiency (PCE) (22.18%) than the control (20.89%) and Cd-Httb (21.56%). Meanwhile, the unencapsulated Cd-Httb-BDC-modified device still maintained 90% of initial PCE after 1500 h in ambient conditions and exhibited enhanced thermal stability (85 °C in N2 atmosphere). This work presented a successful example of mix-ligands strategy on construction of high-quality MOF-assisted perovskite films for high-efficient and stable PSCs.

Large-area large-grain CsPbCl3 perovskite films by confined re-growth for violet photodetectors

CsPbCl3 perovskite is an attractive semiconductor material with characteristics such as a wide bandgap, high chemical stability, and excellent optoelectronic properties, which broaden its application prospects for ultraviolet (UV) and violet photodetectors (PDs). However, large-area CsPbCl3 films with high coverage, large grains, and controllable thickness are still difficult to prepare by using the solution method due to the extremely low solubility of their precursors in conventional solvents. Herein, a water-assisted confined re-growth method is developed, and a CsPbCl3 microcrystalline film with an area of 3 cm × 3 cm is grown, the thickness of which is controllable within a range of several microns. The as-prepared thin film exhibits a flat and smooth surface, large grains, and enhanced photoluminescence. Furthermore, the fabricated violet PDs based on the prepared CsPbCl3 film show a high responsivity of 2.17 A W−1, external quantum efficiency of 664%, on/off ratio of 2.58 × 103, and good stability. This study provides a prospective solution for the growth of large-area, large-grain, and surface-smooth CsPbCl3 films for high-performance UV and violet PDs.

Multifunctional interface modifier ammonium silicofluoride for efficient and stable all-inorganic CsPbBr3 perovskite solar cells

Through passivating interfacial defects and improving energy level alignment and perovskite quality, ASF as interface modifier helps all-inorganic CsPbBr 3 PSCs achieve a champion PCE of 10.08% and excellent moisture and heat tolerance. • The interface modification of ASF passivates the defects of TiO 2 and perovskite. • The energy level alignment at TiO 2 /CsPbBr 3 interface is improved by modifying ASF. • A large-grained perovskite film is formed on the ASF-modified TiO 2 ETLs. • The ASF-modified CsPbBr 3 PSCs achieve a best PCE of 10.08% and excellent stability. The interfacial modification has been considered as an effective strategy to build high-efficient and stable perovskite solar cells (PSCs) by reducing the loss of charge recombination and energy at electron transport layers (ETLs)/perovskite interface. Here, a multifunctional inorganic salt of ammonium silicofluoride (ASF) is utilized as an interfacial modifier to incorporate at TiO 2 ETLs/CsPbBr 3 perovskite interface, which decreases the surface oxygen vacancy defects of TiO 2 by its bonding with silicofluoride anion and adjusts the energy level of TiO 2 by dipole effect to minimize interfacial band difference, resulting in a promotion of electrons extraction and a reduction of energy loss. Simultaneously, the ASF modification affords a more hydrophobic TiO 2 substrate for the constitution of perovskite film with larger crystal and passivates anion defects of CsPbBr 3 film via the formation of hydrogen bonds between the H atom in ammonium cations and Br atom in perovskite, which dramatically inhibits the recombination of carriers. Finally, the all-inorganic CsPbBr 3 PSCs based on the ASF-modified TiO 2 ETL achieves a remarkable higher power conversion efficiency of 10.08%, compared to 6.84% efficiency of the control device. In addition, the long-term tolerance of the device without encapsulation towards high humidity and high temperature is significantly enhanced after interface modifying with ASF.

Improved electrical properties of cuprous thiocyanate by lithium doping and its application in perovskite solar cells

Perovskite solar cells have attracted extensive attention because of their photoelectric characteristics. Since 2009, the photoelectric conversion rate of the solar cells has soared from 3.8% to 25.7% now. Perovskite materials have become the focus of extensive academic research due to their advantages of high carrier mobility, low exciton binding energy, wide absorption spectrum and high optical absorption coefficient However, organic P-type semiconductor materials are usually used as the hole transport layer in high efficiency perovskite solar cells. For example, Spiro-OMeTAD, PEDOT: PSS, PTAA, etc. Because Spiro-OMeTAD is difficult to be purified, many hole transport materials containing triphenylamine like Spiro-OMeTAD have been synthesized, such as triphenylamine polymer PTAA. As the conjugate parts of these triphenylamine transport materials are not coplanar and the space is distorted, they cannot form ordered stacks by spin-coating method, so their charge properties are weak, and li-TFSI and tBP are often added to improve the hole transport, so as to achieve better device effects. Moreover, PTAA has the problem of infiltration, and it is difficult to form a completely covered perovskite film on it, which seriously affects the quality and surface morphology of perovskite film. PEDOT: PSS itself has an acidic and corrosive electrode, and is easy to absorb moisture, which will affect the stability of the solar cell. The performance of organic materials will deteriorate seriously under environmental factors such as humidity, temperature and UV irradiation, which will accelerate the aging of perovskite solar cells and become one of the main obstacles to their practical application. In this work, inorganic cuprous thiocyanate (CuSCN) was used as a hole transport material, CuSCN is a rich and stable P-type semiconductor material, which has the characteristics of abundant, low cost, high carrier mobility, appropriate energy level, low defect density, good thermal stability and excellent light transmittance. CuSCN is one of the few known compounds with both high optical transparency (its wide band gap is 3.7-3.9 eV) and significant P-type electrical conductivity. Most importantly, CuSCN is inexpensive and can be prepared by solution method at room temperature. And its hole transport properties were improved by lithium doping. On this basis, the surface of CuSCN was modified with PTAA to avoid the interaction between CuSCN and lead iodide (PbI<sub>2</sub>), and the preparation of large-grained and dense perovskite films was realized. Finally, the performance of perovskite solar cells was effectively improved. This work provides a reference strategy for the preparation of stable and efficient perovskite solar cells.

Improved electrical properties of cuprous thiocyanate by lithium doping and its application in perovskite solar cells

Perovskite solar cells have attracted extensive attention because of their photoelectric characteristics. Since 2009, the photoelectric conversion rate of the solar cells has soared from 3.8% to 25.7%. Perovskite material has become a focus of extensive academic research due to its advantages of high carrier mobility, low exciton binding energy, wide absorption spectrum and high optical absorption coefficient. However, organic P-type semiconductor material is usually used as a hole transport layer in high efficiency perovskite solar cells, for example, Spiro-OMeTAD, PEDOT:PSS, and PTAA. Because Spiro-OMeTAD is difficult to purify, many hole transport materials containing triphenylamine like Spiro-OMeTAD have been synthesized, such as triphenylamine polymer PTAA. As the conjugate parts of these triphenylamine transport materials are not coplanar and the space is distorted, they cannot form ordered stacks by spin-coating method, so their charge properties are weak, and li-TFSI and tBP are often added to improve the hole transport, so as to achieve better device effects. Moreover, the PTAA has the problem of infiltration, and it is difficult to form a completely covered perovskite film on it, which seriously affects the quality and surface morphology of perovskite film. The PEDOT:PSS itself has an acidic and corrosive electrode, and is easy to absorb moisture, which will affect the stability of the solar cell. The performance of organic material will deteriorate seriously under environmental factors such as humidity, temperature and UV irradiation, which will accelerate the aging of perovskite solar cells and become one of the main obstacles to their practical applications. In this work, the inorganic cuprous thiocyanate (CuSCN) is used as a hole transport material, the CuSCN is a rich and stable P-type semiconductor material, which has the characteristics of abundance, low cost, high carrier mobility, appropriate energy level, low defect density, good thermal stability, and excellent light transmittance. The CuSCN is one of the few known compounds with both high optical transparency (its wide band gap is 3.7–3.9 eV) and significant P-type electrical conductivity. Most importantly, CuSCN is inexpensive and can be prepared by solution method at room temperature. And its hole transport properties are improved by lithium doping. On this basis, the surface of CuSCN is modified with PTAA to avoid the interaction between CuSCN and lead iodide (PbI<sub>2</sub>), and the large-grained and dense perovskite films are prepared. Finally, the performance of perovskite solar cells is effectively improved. This work provides a reference for the preparation of the stable and efficient perovskite solar cells.

Vapor deposition of CsPbBr3 thin films by evaporation of CsBr and PbBr2

Thin films of the inorganic halide perovskite, CsPbBr3, find applications in various optoelectronic devices, including solar cells, radiation detectors, light-emitting diodes, photodetectors, and lasers. Physical vapor deposition (PVD) by coevaporation of CsBr and PbBr2 onto a substrate is a scalable solventless approach to forming high purity large-grained polycrystalline films. Herein, we investigate the effects of deposition temperature, between 26 and 162 °C, and postdeposition annealing, between 250 and 350 °C, on the structure, texturing, and morphology of orthorhombic CsPbBr3 films formed by PVD. All films, regardless of the stable phase at the deposition temperature, transform to orthorhombic upon cooling to room temperature. The films deposited as orthorhombic or tetragonal CsPbBr3 below 130 °C were textured in the orthorhombic structure's ⟨202⟩ direction, while cubic CsPbBr3 films deposited above 130 °C were textured in the orthorhombic structure's ⟨121⟩ direction. This texturing favors the growth of high cation density planes of the stable phase at the deposition temperature. The orthorhombic ⟨202⟩ texturing also dominates after annealing as long as the films have ⟨202⟩ aligned grains before annealing.

(Invited) Rational Strategies for Efficient Perovskite Solar Cells

The past decade has witnessed tremendous advances in organometal halide perovskite solar cells (PSCs) due largely to the stellar set of optoelectronic properties of perovskites such as high absorption coefficient, long carrier diffusion length, and low electron–hole recombination rate constant. Notably, the organolead halide PSC has reached a certified champion power conversion efficiency (PCE) of 25.2%. Rapid progress in PCE has been realized by structure design, materials chemistry, process engineering, and device physics. In this talk, I will first introduce a meniscus-assisted solution printing method (MASP) towards large-grained perovskite films for morphology and crystallinity control. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparted the diffusion of perovskite solutes, thus facilitating the growth of micrometer-scale perovskite grains, leading to perovskite film with good crystallization and preferred orientation. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics. Secondly, I will demonstrate an interesting interface engineering approach with 2D ambipolar black phosphorene (BP) for high-efficiency and stable PSCs. BP carries a stellar set of physical properties such as conveniently tunable bandgap and extremely high ambipolar carrier mobility. Concurrently enhanced carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces was achieved through judicious design and position of BP with tailored thickness as dual-functional nanomaterials. Thirdly, a spatial poling approach will be introduced for perovskite recrystallization towards preferred orientation, crystallinity, and morphology. Finally, the challenges facing the future development and commercialization of PSCs will be summarized and provided.

Grain size dependent photoresponsivity in GaAs films formed on glass with Ge seed layers

The strong correlation between grain size and photoresponsivity in polycrystalline GaAs films on glass was experimentally demonstrated using Ge seed layers with a wide range of grain sizes (1‒330 μm). The crystal evaluations using Raman spectroscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy revealed that 500-nm-thick GaAs films epitaxially grown from the Ge seed layers at 550 °C inherited the grain boundaries and crystal orientations in Ge. With increasing grain size, the photoresponsivity corresponding to GaAs increased from 0.01 to 3 A W−1 under a bias voltage of 0.3 V. The maximum value approached that of the GaAs film formed simultaneously on a single-crystal Ge wafer, indicating the high potential of the large-grained GaAs film. Knowledge gained from this study will be essential for designing advanced solar cells based on polycrystalline III–V compound semiconductors using inexpensive substrates.

Grains level evaluation and performance enhancement for piezoelectric energy harvester

The Internet of things (IoT) is gaining popularity due to diverse applications and market potential. They are pushed more into remote locations and developers look for a perpetual power source. The vibration energy harvester (EH) is capable to mitigate powering issues. Zinc oxide (ZnO), Polydimethylsiloxane (PDMS) and Silver (Ag) were used. However, it is observed that film grains size has a great impact i.e. large-grained films are superior to small-grained films. This work analyses impacting parameters and relevant empirical study. Scanning-Electron-Microscope (SEM), X-ray Diffraction (XRD), Electrical characterization were carried out for in-depth analysis. It is observed that 46.92 µWpeak/15.03 µWrms power is achieved in this work.

Tailoring the Optical Response of Pentacene Thin Films via Templated Growth on Hexagonal Boron Nitride.

The optoelectronic properties of organic thin films are strongly dependent on their molecular orientation and packing, which in turn is sensitive to the underlying substrate. Hexagonal boron nitride (hBN) and other van der Waals (vdW) materials are known to template different organic thin film growth modalities from conventional inorganic substrates such as SiO2. Here, the morphology and temperature-dependent optical properties of pentacene films grown on hBN are reported. Pentacene deposited on hBN forms large-grain films with a molecular π-face-on orientation unlike the dendritic edge-on thin-film phase on SiO2. Pentacene/hBN films exhibit a 40 meV lower free exciton emission than pentacene/SiO2 and an unconventional emission energy temperature dependence. Time-resolved photoluminescence (PL) decay measurements show a long-lived signal in the π-face-on phase related to delayed emission from triplet-triplet fusion. This work demonstrates that growth on vdW materials provides a pathway for controlling optoelectronic functionality in molecular thin films.

Low-Temperature Deposition of Large-Grained Polycrystalline AlN Using Trisdimethylamido Aluminum (TDMAA) and Anhydrous Hydrazine

High quality, large-grained AlN films are of interest for use as either heat spreading layers or as a buffer/templating layer for further film growth. As the typical deposition temperature for high-quality crystalline AlN is usually in excess of 800 oC, there is a large amount of thermal strain in the films and it is advantageous to develop processes to lower the deposition temperature so that it is compatible with back end of line (BEOL) processing. In this work, the low-temperature (<400 oC) deposition of polycrystalline AlN films is demonstrated by atomic layer annealing (ALA) which is a variant of ALD that utilizes a third pulse of low-energy inert gas ions in addition to the usual metal and co-reactant pulses [1].Using trimethyl aluminum (TMA) or tris(dimethylamido) aluminum (TDMAA) with the highly reactive nitrogen-containing precursor hydrazine (N2H4), AlN can be deposited at ~200 oC [2]; however, these films are amorphous and would have low thermal conductivity due to a high degree of phonon scattering. Using TDMAA with N2H4 or NH3 at temperatures >350 oC, polycrystalline films can be deposited in a purely thermal process; however, the reported grain sizes are small (<5 nm) or there is a mixture of polycrystalline and amorphous phases [3-4]. ALA has been used to deposit crystalline films such as AlN [1,5] and GaN [6] on a near lattice-matched substrate (sapphire) at low temperatures, but a nitrogen-containing plasma was used.In the present study of AlN ALA on Si (111) (a non-lattice matched substrate), two metal precursors (TMA and TDMAA) were compared using ultra-high purity anhydrous N2H4 as a co-reactant and argon ions with tuned energy for the third pulse. It was found that deposition using TDMAA as the Al precursor resulted in high-quality AlN films with large grain size (>20 nm) and low C/O contamination (<1.5%) whereas films deposited using TMA had much higher carbon content (>5%), owing to its thermal instability at 400 oC. Transmission electron micrographs for a 40 nm film grown using TDMAA and N2H4 show vertical grain structure with grains spanning the entire thickness of the film. As heat spreading layers often need to be in excess of 1 micron thick in order to be relevant for use in high volume manufacturing, it is also demonstrated that these 40 nm films successfully transfer the large grain size of the ALA film to a thick sputtered AlN film (which can be deposited relatively quickly) by acting as a template layer.[1] H-Y. Shih et al, Scientific Reports 7:39717.[2] M. Mizuta et al, Japanese J. Appl. Phys. 25(12), L945-L948 (1986).[3] R. G. Gordon, U. Riaz, and D. M. Hoffman, J. Mater. Res., 7(7) (1992).[4] A. I. Abdulagatov et al Russian Microelec. 47(2), 118-130 (2018).[5] W-C. Kao et al, RSC Adv. 9, 12226-12231 (2019).[6] W-H. Lee et al ACS Sustainable Chem. Eng. 7,1, 487-495 (2019).This work was supported in part by the Semiconductor Research Corporation. Figure 1

The effect of methyl ammonium chloride doping for perovskite solar cells on structure, crystallization and power conversion efficiency

The perovskite membrane with large particle size, uniform coverage and high quality is the prerequisite for the preparation of efficient and stable perovskite solar cells. Various additives have been used to increase the grain size and improve the film morphology and crystal quality. In this paper, methylammonium chloride (MACl) was proposed to obtain high crystalline quality of [Formula: see text] perovskite absorption layer. The results show that the adding ammonium methyl chloride into the precursor of tricationic perovskite not only passivates surface defects to form high-quality and large-grain perovskite films, but also facilitates the formation of pure [Formula: see text]-phase [Formula: see text]. Meanwhile, the designed perovskite precursor solutions were used to fabricate mesoporous perovskite solar cells (PSCs). Owing to the perovskite layer consisting of optimized MACl doping, the short-circuit current density [Formula: see text] of PSCs reaches 23.81 mA/cm2, which is 2.73 mA/cm2 higher than the primary [Formula: see text] based on PSCs. The obtained power conversion efficiency (PCE) increases from 13.67% to 17.59%.