Silicon is the second abundant element on earth. The energy gap for silicon is very suitable to absorb energy in solar spectrum. Since as early as the year of 1954 when Bell Lab published the first application of P/N junction subject to light irradiation to generate electric current in solar cell, silicon solar cell has always been the mainstream technology in the market. Commercial silicon solar cell includes single crystal silicon type and poly crystal silicon type. Solar cell manufacturing comprises diffusion process to form P-N junction on silicon wafer, PECVD to produce antireflective layer, and screen printing to produce conductive metal. Upon light irradiation, solar cell can generate photocurrent. Current commercial products have efficiency as high as 14%~17%. Present silicon solar cell technology is developing towards high conversion efficiency and low wafer thickness to save material cost. However, the increased capital cost for process and equipment and the breakage due to thinning wafer are the challenges that must be overcome in the future.
Crystalline Solar Cell
Monocrystalline c-Si Solar Cell
Multicrystalline c-Si Solar Cell
Process Flow of c-Si Solar Cell
Thin film solar cell only requires a very small amount of raw material and has advantages in light weight, thinness and being manufactured as large area and low cost integrated module on flexible substrate. Currently, it is commonly considered as the solar energy technology of most development potential.
CIGS compound semiconductor thin film solar cell has the highest photoelectric conversion about 20%, closet to currently market mainstream crystal silicon efficiency level. It is the highest in thin film technology and has no decay issue. Because it has both advantages in low cost and high efficiency, it is one of the highly anticipated technologies. CIGS is a semiconductor compound that comprises elements of I-III-VI family such as copper, indium, gallium and selenium. By adjusting ratio of each element in the manufacturing process, broad energy band distribution is attained for light absorbing layer. So it can fully absorb light of different wavelengths in solar spectrum and achieve the highest conversion efficiency.
Currently, various technologies can be employed in CIGS manufacturing process and they include vapor co-deposition, sputtering and selenization, wet coating and plating …et al. More and more companies and institutes are attracted to this development field. Thus, breakthrough in CIGS development can be expected soon.
Process Flow of Monolithic interconnection CIGS module
CIGS compound structure
CIGS Spectrum Response
CIGS has wide solar spectrum response and is capable of fully utilizing incident light.
Silicon thin film solar module is thought to be the solar module technology of most development potential because it only needs very small amount of silicon material and has advantages in light weight, thinness, low manufacturing cost and flexibility. Chemical vapor deposition enables the formation of 0.3~2μｍ silicon thin film on glass or flexible substrate. By adjusting thin film deposition parameters or adding different elements, we can obtain silicon thin film material with different energy band gaps to absorb solar light in different wavelengths and attain high photoelectric conversion efficiency. The initial efficiency for current device can reach 15%. Due to excellent temperature coefficient and low irradiance response, under the same solar module system capacity, the silicon thin film solar module produces 10~20% more power every year and provides higher economic benefit. On the other hand, its energy consumption in the manufacturing process is much lower than that for silicon crystal solar module. The energy pay-back time is only about 1.5 years. It is truly an environment-friendly renewable energy technology.
Si Thin Film Tandem Solar Module
By stacking silicon thin film solar module with different energy bands, it is able to fully utilize solar spectrum and increase device efficiency. This device structure is also considered a potentially commercializable technology for high efficiency silicon thin film solar module.
Si Thin Film Solar Cell Process
Silicon thin film solar cell module process is fairly simple. In the front-end process, laser scribing connects every silicon thin film solar cell and forms serial structure. It also increases module voltage. Thus, each silicon thin film solar cell module contains a series of several dozens to several hundreds of silicon thin film solar cells. In the back-end process, the module process is similar to that for silicon crystal solar cell module.