Microcrystalline Silicon Tunnel Junction for Monolithic Tandem Solar Cells Using Silicon Heterojunction Technology

Abstract

In this study, we developed a microcrystalline silicon tunnel junction to be used as a tunnel recombination junction between a large-gap top-cell and a silicon heterojunction bottomcell, in a monolithic tandem integration. This junction is composed of a p-type layer on the top of an n-type layer, deposited by plasma-enhanced chemical vapor deposition at low temperature (200°C). Microcrystalline phase percentage was controlled with Raman spectroscopy and ellipsometry measurements. The total stack has a thickness of 40 nm and an average conductivity around 10 S/cm. Minority carrier lifetime measurements showed an improvement of the field effect and the passivation with the addition of this junction on top of silicon heterojunction solar cells. Moreover, implementation of microcrystalline layer on top of reference rear emitter silicon heterojunction solar cells improved the fill factor and did not induce parasitic absorption above 700 nm. Simple tests structures were fabricated in order to characterize the tunnel junction and optimize it. Then, we carried out dark temperature-dependent I-V measurements on those test structures and observed peaks and valleys, characteristic of the junction tunnel behavior. The developed tunnel junction shows low contact resistivity and activation energies these are promising results for the complete integration on the tandem device.

A Contactless Patterned Plasma Processing for Interdigitated Back Contact Silicon Heterojunction Solar Cells Fabrication

“…After oxide removal via 30 seconds HF dip, uniform layers are deposited on the entire substrate surface: on the rear, a 15 nm intrinsic hydrogenated amorphous silicon ((i)a-Si:H) passivation layer. On the front, the same passivation layer is followed by a 13nm n-type ((n)a-Si:H) back surface field layer, and a 55 nm n-type/p-type hydrogenated microcrystalline silicon ((n)µc-Si:H/(p)µc-Si:H) recombination junction (the use of which in multitechnology multijunctions [6] and micromorph thin film silicon [7] designs is well documented).…”

Controlling Diffusion in Poly-Si Tunneling Junctions for Monolithic Perovskite/Silicon Tandem Solar Cells

“…An alternative are Si-based tunneling junctions (SiTJs), as first demonstrated in a perovskite/Si tandem cell by Mailoa et al [9], which have the benefit of better refractive index matching between the subcells and thus reducing reflection losses [10]. Additionally, they have the potential to be directly integrated in the processing of the bottom cell's passivating contact [11]- [15]. Compared to silicon heterojunction (SHJ)-based SiTJ, poly-Si-based passivating TJs [11], [14] have the benefit of higher thermal stability, making them compatible with the mainstream Si solar cell structure, i.e., the passivated emitter and rear cell (PERC) technology [16] [see Fig.…”

Monolithic Perovskite/Silicon-Heterojunction Tandem Solar Cells with Nanocrystalline Si/SiOx Tunnel Junction

“…The combination of thin TCO and an optical interlayer with higher refractive index (~2.6 at 800 nm) has been recently proposed for improved infrared light management and applied also in record tandem solar cells [5,10]. Alternatively, the integration of a p/n recombination junction made of higher-index doped nanocrystalline Si has been proposed as a replacement of the TCO recombination layer [9,19].…”

“…In this work, we focus on a p/n tunnel junction based on doped nanocrystalline silicon/silicon-oxide layers deposited by plasma enhanced chemical vapor deposition (PECVD), building on the approaches of references [9,10,19]. This component is meant to act as an interband tunnel junction [15].…”