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CIGS Solar Batteries Bring New Possibilities to Wearables

By Ding Yu Shan
Published: Aug 14,2015

People all around the world are considerably enthusiastic about developing eco-friendly resources, and governments of all nations hope to be able to increase the proportion of renewable energy sources. Of all the feasible renewable energy sources, such as solar power, hydroelectric power, geothermal power, and tidal power, solar energy is currently recognized as the cleanest renewable energy source, not to mention the most ubiquitous and commonly encountered.

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Even though solar rays appear to be inexhaustible, solar energy usually requires batteries to store electricity. At this stage a number of scientists are engaged in research into solar battery systems and attempting to use various materials to manufacture solar batteries in order to attain the most efficient methods of photovoltaic power generation.

At this stage, the most common types of materials used in solar batteries are silicon chips, CdTe film, CIGS film, dye-sensitized film, and organic materials; however, the most commonly encountered materials for solar batteries are silicon chips and types of thin films.

Solar batteries with thin films have received the most attention of these two types because they are flexible, foldable, and can be used for a wide range of purposes.

At Taiwan’s Industrial Research Institute (ITRI), the team led by Project Manager Chien-Chih Chiang of the Green Energy and Environment Research Laboratories has developed a thin film solar battery using Copper Indium Gallium Diselenide (CIGS).

The two main types of CIGS solar batteries are vacuum manufactured and non-vacuum manufactured. The CIGS solar battery developed by ITRI is manufactured using a non-vacuum process based on the principle of placing a layer of Molybdenum electrode sputter beneath the ultra-thin and flexible stainless steel base plate.

Using the CIG (copper, indium and gallium) nano paste, which was independently researched and developed by ITRI, as an applicant blade and silt coating and then after using a layer of CIG precursor to coat the stainless steel base plate, it will undergo a 500℃ heat treatment to make the CIG precursor form into a metal alloy.

It is worth noting that ITRI uses Taiwan’s first hydrogen selenide laboratory to introduce a specific proportion of Se into the CIG alloy in order to form the CIGS compound. This action produces the key absorption layer for when the solar batteries absorb light energy and convert it into electrical energy. Finally, there is also the coated buffer layer, the transparent conductive layer, and the metal electrodes and protection layer.

Figure 1 :   Film solar batteries are flexible, foldable, and can be used for a wide range of purposes.
Figure 1 : Film solar batteries are flexible, foldable, and can be used for a wide range of purposes.

The performance of CIGS batteries in terms of energy conversion efficiency are excellent, and they can be used in limitless categories of applications. In addition, they have numerous other advantages, such as low manufacturing costs and requiring only modest amounts of energy and materials.

As for energy conversion efficiency, currently international research has produced an energy conversion efficiency rate of 21.7% for vacuum manufactured batteries, which is competitive with the energy capacity and transformation efficiency rate of 20.4% found in many silicon chip solar batteries. However, ITRI’s non-vacuum manufactured batteries are capable of reaching a rate of 14.6%.

Chien-Chih Chiang stated that at first it had a worthless capacity efficiency of only 2%, but after passing through several barriers, it rose to 9%. Upon the discovery of new manufacturing processes, the rate rose to 12%, and after it received more attention and became a focal point of development, it won the 26th and 27th annual EU PVSEC awards for top thesis posters in the category of thin film solar batteries.

Although non-vacuum manufactured batteries have a lower capacity efficiency than vacuum manufactured batteries and the technology poses greater difficulties, compared to vacuum manufactured batteries, which have a material utilization rate of only 30%, non-vacuum manufactured batteries have a material utilization rate of over 95%. In addition, they require less time to manufacture, and they only require 30% of the investment in instruments and equipment needed to produce vacuum manufactured batteries.

The cost of producing electricity with non-vacuum manufactured batteries is expected to drop down to 0.5 to .65 US$ per Watt, which makes the cost of producing non-vacuum manufactured CIGS solar batteries extremely competitive with other technologies.

Figure 2 :   CIGS solar batteries have numerous advantages, including better energy conversion efficiency and low productions costs.
Figure 2 : CIGS solar batteries have numerous advantages, including better energy conversion efficiency and low productions costs.

In addition to having ideal production costs, the special properties of the thin film enable CIGS solar batteries to be used in soft and flexible panels. Therefore, the scope of applications can be expanded into areas that were impossible for the hard silicon solar cells of the past, such as wearable electronic products, clothing, and backpacks.

At the same time, the unique characteristics of soft and flexible panels make them more flexible and suitable for applications on the surfaces of architectural structures or combined awnings and curtains, and they are capable of increasing the effectiveness of solar battery installations. In addition to this, CIGS solar batteries can also be incorporated into roll-to-roll printing processes in order to lower both their production costs and the amount of time required to manufacture them.

With the constantly increasing demand for renewable energy, solar power has already become a major growth driver, and with their plethora of strong points, the development prospects and potential are limitless for non-vacuum manufactured CIGS solar batteries. Therefore, it is to be expected that they will be of great assistance in the future development of renewable energy sources.

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