High-mobility Hydrogenated Indium Oxide without Introducing Water During Sputtering

AbstractThe key role of water to obtain high-mobility IO:H (hydrogenated indium oxide) layers has been well documented, but introducing the required tiny amount of water is technologically challenging. We first use simulations to evidence the key role of high mobility for the transparent conductive oxide for high-efficiency crystalline silicon solar cells. Then, we investigate an approach to fabricate high-mobility IO:H that circumvent the introduction of water vapor, relying on water vapor from ambient air. A sputtering tool equipped with a residual gas analyzer allows partial pressure monitoring of hydrogen and water in the system, and to link the gas composition to the properties of the deposited films. To vary the residual water pressure, we varied the pumping time after opening the chamber and before starting the deposition to reach different base pressures (1. 10-5 mbar to 3. 10-7 mbar), which are mostly composed of residual water. An optimum base pressure around 3. 10-6 mbar—and not lower pressures—was found to yield the highest mobility values after annealing. An alternative approach by introducing a small flow of hydrogen together with argon and oxygen is also shown to provide promising results

Tin(IV) Oxide Electron Transport Layer via Industrial-Scale Pulsed Laser Deposition for Planar Perovskite Solar Cells

Electron transport layers (ETL) based on tin(IV) oxide (SnO2) are recurrently employed in perovskite solar cells (PSCs) by many deposition techniques. Pulsed laser deposition (PLD) offers a few advantages for the fabrication of such layers, such as being compatible with large scale, patternable, and allowing deposition at fast rates. However, a precise understanding of how the deposition parameters can affect the SnO2 film, and as a consequence the solar cell performance, is needed. Herein, we use a PLD tool equipped with a droplet trap to minimize the number of excess particles (originated from debris) reaching the substrate, and we show how to control the PLD chamber pressure to obtain surfaces with very low roughness and how the concentration of oxygen in the background gas can affect the number of oxygen vacancies in the film. Using optimized deposition conditions, we obtained solar cells in the n¿i¿p configuration employing methylammonium lead iodide perovskite as the absorber layer with power conversion efficiencies exceeding 18% and identical performance to devices having the more typical atomic layer deposited SnO2 ETL

Pulsed Laser Deposition of Cs2AgBiBr6: from Mechanochemically Synthesized Powders to Dry, Single-Step Deposition

Cs2AgBiBr6 has been proposed as a promising lead-free and stable double perovskite alternative to hybrid and lead-based perovskites. However, the low solubility of precursors during wet synthesis, or the distinct volatility of components during evaporation, results in complex multistep synthesis approaches, hampering the widespread employment of Cs2AgBiBr6 films. Here, we present pulsed laser deposition of Cs2AgBiBr6 films as a dry, single-step and single-source deposition approach for high-quality film formation. Cs2AgBiBr6 powders were prepared by mechanochemical synthesis and pressed into a solid target maintaining phase purity. Controlled laser ablation of the double perovskite target in vacuum and a substrate temperature of 200 °C results in the formation of highly crystalline Cs2AgBiBr6 films. We discuss the importance of deposition pressure to achieve stoichiometric transfer and of substrate temperature during PLD growth to obtain high-quality Cs2AgBiBr6 films with grain sizes > 200 nm. This work demonstrates the potential of PLD, an established technique in the semiconductor industry, to deposit complex halide perovskite materials while being compatible with optoelectronic device fabrication, such as UV and X-ray detectors

Chalcohalide Antiperovskite Thin Films with Visible Light Absorption and High Charge-Carrier Mobility Processed by Solvent-Free and Low-Temperature Methods

Silver chalcohalide antiperovskites represent a rather unexplored alternative to lead halide perovskites and other semiconductors based on toxic heavy metals. All synthetic approaches reported so far for Ag3SI and Ag3SBr require long synthesis times (typically days, weeks, or even months) and high temperatures. Herein, we report the synthesis of these materials using a fast and low-temperature method involving mechanochemistry. Structural and optical properties are examined experimentally and supported by first-principles calculations. Furthermore, we deposit Ag3SI as thin films by pulsed laser deposition and characterize its optoelectronic properties using optical-pump-terahertz-probe measurements, revealing a high charge-carrier mobility of 49 cm2 V-1 s-1. This work paves the way to the implementation of chalcohalide antiperovskites in various optoelectronic applications

Amorphous gallium oxide grown by low-temperature PECVD

Owing to the wide application of metal oxides in energy conversion devices, the fabrication of these oxides using conventional, damage-free, and upscalable techniques is of critical importance in the optoelectronics community. Here, the authors demonstrate the growth of hydrogenated amorphous gallium oxide (a-GaOx:H) thin-films by plasma-enhanced chemical vapor deposition (PECVD) at temperatures below 200 °C. In this way, conformal films are deposited at high deposition rates, achieving high broadband transparency, wide band gap (3.5-4 eV), and low refractive index (1.6 at 500 nm). The authors link this low refractive index to the presence of nanoscale voids enclosing H2, as indicated by electron energy-loss spectroscopy. This work opens the path for further metal-oxide developments by low-temperature, scalable and damage-free PECVD processes

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Scalable Vacuum-Based Deposition Methods for Halide Perovskites

A thesis on four distinct vacuum-based deposition technqiues for halide perovskites, being pulsed laser deposition, co-sublimation, flash evaporation, and close-space sublimation

Incremental Feeding of Perovskite Powders: Angstrom-Precision Growth for Single-Source Solar Cell Fabrication

Vacuum-based deposition of halide perovskites receives a lot of attention for its proven scalability and conformal depositions. Co-evaporation has remarkable success, but efficiencies continue to lag behind their solution-based counterparts. This is in part attributed to the complex sublimation behavior of some organic ammonium precursor salts and the increased complexity of the absorber materials, requiring the use of four or more sources in a conventional co-evaporation setup. The latter has driven work into single-source methods with flash evaporation presented as one such method. However, flash evaporation processes typically evaporate all material in a single batch, leading to short deposition times at high temperatures. Particle sputtering effects seen at these high temperatures drive processes toward low temperatures where prolonged exposure causes degradation. Here, a pulse-driven incremental powder feeding system is presented. This method is capable of stable flash evaporation rates for >1 h, with controlled rates as low as 1.5 Å per pulse (±0.89). The feasibility of this method is demonstrated for three different perovskite compositions: FAPbBr3, MAPbI3, and FA1−xMAxPbSnI3:SnF2. Furthermore, FAPbBr3 and MAPbI3 are integrated into all vacuum-processed thin-film solar cells leading to power conversion efficiencies (PCE) of ~4% and 10%, respectively