Abstract
Interfacial oxide layer plays a crucial role in a MoOx/ n -Si heterojunction (MSHJ) solar cell; however, the nature of this interfacial layer is not yet clarified. In this study, based on the experimental results, we theoretically analyzed the role of the interfacial oxide layer in the charge carrier transport of the MSHJ device. The interfacial oxide layer is regarded as two layers: a quasi p -type semiconductor interfacial oxide layer (SiOx(Mo))1 in which numerous negatively charged centers existed due to oxygen vacancies and molybdenum–ion-correlated ternary hybrids and a buffer layer (SiOx(Mo))2 in which the quantity of Si-O bonds was dominated by relatively good passivation. The thickness of (SiOx(Mo))1 and the thickness of (SiOx(Mo))2 were about 2.0 nm and 1.5 nm, respectively. The simulation results revealed that the quasi p -type layer behaved as a semiconductor material with a wide band gap of 2.30 eV, facilitating the transport of holes for negatively charged centers. Additionally, the buffer layer with an optical band gap of 1.90 eV played a crucial role in passivation in the MoOx/ n -Si devices. Furthermore, the negative charge centers in the interfacial layer had dual functions in both the field passivation and the tunneling processes. Combined with the experimental results, our model clarifies the interfacial physics and the mechanism of carrier transport for an MSHJ solar cell and provides an effective way to the high efficiency of MSHJ solar cells.
Highlights
As a novel structure for a silicon-based solar cell, selective passivated contact has attracted much attention in recent years due to its successful transport of majority charge carriers and the reduction of the recombination rate of minority charge carriers [1,2,3,4,5,6,7]
We found that a 3.5 nm ternary-like hybrid layer of a-SiOx(Mo) formed between the MoOx and the n-Si substrate, and that the hybrid layer might have played a vital role in the good performance of the MoOx/n-Si heterojunction (MSHJ) solar cells
The subsequent simulation results demonstrated that this interfacial layer SiOx(Mo)1 was a Mo-based semiconductor material with a wide optical band gap of ~2.30 eV and negative charge centers with densities in the range of 1011-1012 cm-2
Summary
As a novel structure for a silicon-based solar cell, selective passivated contact has attracted much attention in recent years due to its successful transport of majority charge carriers and the reduction of the recombination rate of minority charge carriers [1,2,3,4,5,6,7]. It has been reported that a 7 nm-thick MoOx film has been used to replace the a-Si:H(p) layers in SHJ devices, resulting in a conversion efficiency of 22.5% [13]. We demonstrated a different MoOx/n-Si SHJ solar cell with an efficient hole collection and simple fabrication process by evaporating MoO3 powder onto an n-type silicon. The high work function of the MoOx layer induced an interfacial inversion layer in the surface of the n-Si substrate, forming the build-in-potential, it was not negligible that the 3.5 nm interfacial oxide layer played a significant role in the transport of carriers. The simulation results help us achieve an effective way to the high efficiency from the clarification of the interfacial physics in the MSHJ solar cells
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