On the Electron Transport in Simplified IBC-SHJ Solar Cells With MoOx Blanket Layer

Abstract

Interdigitated-back-contacted silicon heterojunction (IBC-SHJ) solar cells with molybdenum oxide (MoO_x) as a hole transport layer and a novel (n)-type hydrogenated nanocrystalline silicon (nc-Si:H)/MoO_x electron transport stack use ultra-thin MoO_x as a full-area blanket layer. This solar cell architecture is realized with a simplified fabrication process and ensures high shunt resistances, attributed to the low lateral conductivity of the MoO_x layer. Here we investigate the electron transport mechanisms through the electron collection contact to improve the understanding and performance of the IBC-SHJ solar cells. For this evaluation, we first introduce plasma treatments between (n)nc-Si:H and MoO_x and assess their role in passivation, charge carrier transport and MoO_x growth. Temperature-dependent current–voltage (I–V) measurements of front/back-contacted (FBC) solar cells with (n)nc-Si:H/MoO_x stack, supported by high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX) imaging and numerical simulations, reveal that plasma treatment (PT) and plasma treatment with boron (PTB) enable electron transport based on direct energy transitions. Next, we perform thickness sensitivity analysis to find the optimal layer thicknesses of (n)nc-Si:H and MoO_x. While FBC-SHJ devices exhibit stable performance across a broad range of (n)nc-Si:H thicknesses (10–50 nm), IBC-SHJ devices are more sensitive to such a thickness variation, with thinner (n)-layers limiting final device efficiency. The combination of 50-nm thick (n)nc-Si:H, PTB, and 1.7-nm thick MoO_x enables the best performance of IBC-SHJ solar cells. When metallized with electroplated Cu, our champion IBC-SHJ solar cell with MoO_x blanket layer reaches an efficiency of 23.59%. Further advancements in (n)nc-Si:H properties, passivation, transparent conductive oxide selection, and front-side light management are expected to drive efficiencies well above 24%.