H OW EFFICIENT MODERN SOLAR CELLS WORK. Yuichi Irisawa

S OLAR CELLS Solar cells convert sunlight to electricity directly Solar cells are classified some types Silicon Inorganic compound semiconductor Mono crystal Poly crystal Amorphous HIT CdTe CIGS

M ECHANISM OF SOLAR CELLS 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 Sunlight Current N-type silicon P-type silicon P-N junction Front electrode Back electrode Load ElectronProton

H OW 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% Module typeEfficiency Crystal silicon13~17% Thin film silicon15% Compound13% Crystal silicon (in lab)More than 24%

F ACTOR OF THE SOLAR CELLS EFFICIENCY Spectral responseTransmittance and reflectivity of cover glass 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 Wave length (nm) Si sensibility CIS sensibility Sunlight spectrum Spectral response Sunlight Reflected light Transmitted light Solar cell Cover glass

I MPROVE THE SOLAR CELLS EFFICIENT 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 Middle layer Cover glass Back electrode Amorphous cell Front electrode Microcrystal Si cell Short wave length Long wave length

C ONCLUSION 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

W HAT DEFINITION OF EFFICIENT IS ? The efficient of photovoltaic is defined by Out put power [W] Sunlight energy [W/m 2 ] * Module area [m 2 ] * 100 (%)