Effect of the Vertical Transportation Component of the TCO Layer on the Electrical Properties of Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells that consist of thin amorphous silicon layers and crystalline silicon substrate are known as the high-efficiency class of solar cells. To collect the charge carriers, transparent conductive oxide (TCO) layers are inserted in which the charge carriers are being either vertically or both laterally and vertically transported. In this study, we have investigated the effect of the vertical transportation component of aluminum-doped zinc oxide (AZO) layers on the electrical properties of the fabricated SHJ solar cells and its contribution to the total series resistance of the obtained devices. In order to separate the vertical from the lateral transportation, we have employed an AZO/Ag/AZO multilayer structure, which only allows the vertical transportation of the charge carriers within the AZO layers. Our results show that with increase in O₂ flow, the reduction rate of the FF is about three times higher when both lateral and vertical conductions take place, compared with when only vertical conduction occurs. Moreover in the latter case, a reduction of ~ 6% in the FF value per unit increase of vertical resistivity is obtained. Finally, we validate our procedure by comparing the obtained experimental results with the theoretically modeled values. The validation delivered a good agreement.