Month: July 2022

Evaporation Coating Experiment: Principle, Purpose & Results

Introduction

In recent years, the rapid economic development and the continuous improvement of people’s living standards have led to the continuous emergence of high-tech thin-film products, especially in the field of electronic materials and components. Vacuum coating technology has also gained significant application in this field.

At present, the common film-forming methods include vapor-phase film-forming method, oxidation method, ion implantation method, diffusion method, electroplating method, coating method, liquid-phase growth method, etc. The vapor generation method can be further subdivided into physical vapor deposition, chemical vapor deposition, and discharge polymerization.

Principle

The experiments listed in this article are related to physical vapor deposition coatings. This method is basically carried out under vacuum, so it is called vacuum coating technology.

Vacuum evaporation, sputter coating, and ion plating are commonly referred to as basic physical vapor deposition thin film preparation techniques. The vacuum evaporation coating method is a method in which the evaporation material of a film to be formed in a vaporization chamber is heated in a vacuum chamber, and atoms or molecules are vaporized from the surface to form a vapor stream, which is incident on the surface of the substrate and condensed to form a solid film.

Evaporation Coating

Purposes

  1. To familiarize yourself with the operating procedures and methods obtained by vacuum;
  2. In order to understand the principle and method of evaporation coating;
  3. To learn how to use evaporation coating technology.

Results

(1) Vacuum conditions during evaporation

When the average free path of the vapor molecules in the vacuum vessel is greater than the distance between the evaporation source and the substrate (called the steaming distance), sufficient vacuum conditions are obtained. For this reason, it is necessary to increase the mean free path of the residual gas to reduce the collision probability of the vapor molecules with the residual gas molecules, and to evacuate the vacuum chamber to a high vacuum.

(2) How to choose evaporation source selection

1 It should have good thermal stability, chemical inactivity; the vapor pressure of the heater itself is sufficient to reach the evaporation temperature.

2 Its melting point should be higher than the evaporation temperature of the evaporated material. The heater should have a large enough heat capacity.

3 The mutual melting of the evaporated material and the evaporation source material must be very low, and it is difficult to form an alloy.

4 The material used for the coil-shaped evaporation source is required to have a good wetting with the evaporation material and a large surface tension.

5 For a case where it is difficult to form a filament, or when the surface tension of the evaporation material and the filament evaporation source is small, a boat-shaped evaporation source can be used.

(3) Main physical processes of thermal evaporation coating

1 Using various forms of thermal energy conversion to vaporize or sublimate the coating material into gaseous particles (atoms, molecules or atomic groups) with certain energy (0.1~0.3eV);

2 Gaseous particles are transported to the substrate by a substantially collision-free linear motion;

3 Particles are deposited on the surface of the substrate and agglomerated into a film.

(4) Factors affecting the quality and thickness of vacuum coating

There are many factors affecting the quality and thickness of the vacuum coating, including the degree of vacuum, the shape of the evaporation source, the position of the substrate, and the temperature of the evaporation source. The solid matter has very low evaporation at normal temperature and normal pressure. The higher the degree of vacuum, the easier it is for the molecules of the evaporation source material to scatter away from the surface of the material. The fewer molecules in the vacuum chamber, the lower the probability that the evaporating molecules will collide with the gas molecules, so that the surface of the substrate can be reached unobstructed straight.

For more information, please visit https://www.samaterials.com/.

Solar Thin Film and Its Technical Advantages

Thin-film solar cells refer to thin films with thicknesses ranging from a few nanometers to tens of microns attached to the solar surface, which make thin-film cells lighter in weight. Thin-film solar cells are used in building-integrated photovoltaics as translucent photovoltaic glass materials that can be laminated to windows.

As a second-generation solar technology, thin-film technology is more affordable than the traditional first-generation c-Si technology, but is less efficient. Therefore, in recent years, people have also paid more attention to the development of sputtering materials and thin film coating technology, and are committed to improving the efficiency of thin film technology. And now it has improved significantly. Laboratory cell efficiencies for CdTe and CIGS are now over 21%, better than polysilicon, the main material currently used in most solar photovoltaic systems. And the life expectancy of thin-film solar cells is also extended to 20 years or more.

Thin film solar cells are made by depositing one or more thin layers or thin films of photovoltaic materials on a substrate such as glass, plastic or metal. In the deposition process, the coating source material used are usually sputtering targets or evaporation materials. Commonly used thin-film solar cell categories include cadmium telluride (CdTe) thin films, copper indium gallium selenide (CIGS) thin films, and gallium arsenide (GaTe) thin films.

The target materials corresponding to the three thin films mentioned above are important materials for the thin film coating of solar cells. Among them, cadmium telluride targets account for 50% of the solar market. On a life cycle basis, CdTe PV has the smallest carbon footprint, lowest water usage, and shortest energy payback time of all solar technologies. With an energy payback period of less than a year, CdTe can reduce carbon emissions faster without short-term energy shortages.

The CIGS sputtering target is composed of four metal elements, namely copper (Cu), indium (In), gallium (Ga) and selenium (Se), and it is also one of the representatives of commonly used targets in the solar industry. CIGS thin film has the advantages of strong light absorption, good power generation stability and high conversion efficiency, which can enable solar cells to generate electricity for a long time during the day and generate a large amount of electricity. CIGS has great advantages in photovoltaic building-integrated applications. At the same time, with the improvement of CIGS conversion efficiency, the self-sufficiency rate of CIGS as a photovoltaic building power supply built with glass curtain walls is also increasing.

GaAs thin-film solar cells have an efficiency of up to 28.8%, which is considered the highest efficiency of all thin films. Gallium arsenide is also resistant to damage from moisture, radiation and UV light. These properties make GaAs thin films an excellent choice for aerospace applications with increased UV and radiation.

For more information, please visit https://www.sputtertargets.net/.