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.