How efficient modern solar cells work.

1. How efficient modern solar cells work. Yuichi Irisawa

2. Solar cells • Solar cells convert sunlight to electricity directly • Solar cells are classified some types Mono crystal Poly crystal Silicon Amorphous HIT CdTe Inorganic compound semiconductor CIGS

3. Mechanism of solar cells Sunlight • Silicon solar cells made by 2 types of silicon • When solar cells are received sunlight, electron and proton moves to front electrode and back electrode • Difference of potential is occurred, So electric current is produced Front electrode N-type silicon Load P-N junction P-type silicon Back electrode Current Proton Electron

4. How efficient solar cells work • The efficiency of solar cells is about 13~17% • The efficiency of solar cells which are developed in laboratory is more than 24%

5. Factor of the solar cells efficiency • Transmittance and reflectivity of cover glass • Spectral response CIS sensibility Sunlight Reflected light Si sensibility Spectral response Cover glass Transmitted light Sunlight spectrum Solar cell Wave length (nm) • Sunlight wave length is mainly distributed from 300nm to 1300nm • Solar cells are more efficient as much as cells receive wide range wave • Cover glass makes sunlight weaken and reflected • Improve to high transmittance and low reflectivity

6. Improve the solar cells efficient Long wave length • Other way, solar cell made from 2 type layer is developing • The cells can receive both short and long wave length sunlight • So “hybrid” solar cells are more efficient than the cells which made from 1 type layer Short wave length Cover glass Front electrode Amorphous cell Middle layer Microcrystal Si cell Back electrode

7. Conclusion • Sunlight moves electron and proton to electrode, so electricity is produced • The solar cells efficiency is about 13~17% • In order to improve efficiency, • Receive more sunlight wave for wide range • High transmittance and low reflectivity of cover glass • “Hybrid” solar cells are effective