Effects of residual copper selenide on CuInGaSe2 solar cells

Large grain and copper-poor CuInGaSe
₂
(CIGS) film is preferred to fabricate high efficiency solar cells. However, the degradation caused by excess copper selenide (Cu
_2-x
Se) is still a problem. This study investigates the formation and behavior of excess CuxSe and further compares the cell performances between typical copper-poor and copper-rich solar cells. As the excess Cu
_2-x
Se can not be exhaust during the growth, the excess Cu
_2-x
Se fully surrounded by the polycrystalline CIGS grain. The CIGS film with excess Cu
_2-x
Se would result in serious shunt paths and poor PN junction. A short circuit in the copper-rich CIGS solar cells can be attributed to the conductive Cu
_2-x
Se. For high efficiency cells, the best way is to exhaust Cu
_2-x
Se during the growth. Or otherwise a dense CIGS film with chemical treatments is necessary to avoid the negative effects of the excess Cu
_2-x
Se.