Investigation of surface features for 17.2% efficiency multi-crystalline silicon solar cells

Abstract

Maskless reactive ion etching (RIE) texturing using a gas mixture of sulfur hexafluoride–oxygen (SF6/O2) and sulfur hexafluoride–oxygen–chlorine (SF6/O2/Cl2) was investigated to reveal the proper shape in surface features for higher efficiency multi-crystalline silicon (mc-Si) solar cells; hence, needle-like and round-top cone (RT cone) shapes were formed by RIE texturing with SF6/O2 gas, and pyramid and inverted pyramid shapes by RIE texturing with SF6/O2/Cl2 gas. RIE-textured mc-Si solar cells were fabricated on these surface features except for an inverted pyramid structure in the industrial production line. Performances of cells with RT cone and pyramid shapes were enhanced, whereas those with a needle-like cone were degraded, compared to the reference cells. Among these cells, those with RT cones represented the highest efficiency at 17.22%. By considering diode characteristics and electroluminescence images of fabricated solar cells, the proper shape for surface features was intimately related to control of the formation of a stable emitter layer as well as the reduction of surface reflectance.