A heterojunction is the interface that occurs between two layers or regions of dissimilar crystalline semiconductors. These semiconducting materials have unequal band gaps as opposed to a homojunction. Silicon heterojunction technology (Si-HJT) is a popular topic in crystalline silicon photovoltaic as it allows for solar cells with energy conversion efficiencies above 20 %, even at industrial-production level. These solar cell consist of thin amorphous silicon layers on monocrystalline silicon wafers.