Yuguo Tao

Fully Ion-Implanted and Screen-Printed 20.2% Efficient Front Junction Silicon Cells on 239 cm

In this study, we present fully ion-implanted screen-printed high-efficiency 239 cm2 n-type silicon solar cells that are fabricated on pseudosquare Czochralski wafers. Implanted boron emitter and phosphorous back-surface field (BSF) were optimized to produce n-type front junction cells with front and back SiO2 /SiNx surface passivation and rear point contacts. Average efficiency of 19.8%, with the best efficiency of 20.2%, certified by Fraunhofer ISE, Freiburg, Germany, was achieved. In addition, the planarized rear side gave better surface passivation, in combination with optimized BSF profile, raised the average efficiency to ~20% for the fully implanted and screen-printed n-type passivated emitter, rear totally diffused cells.

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In this paper, the role of Al content in Ag/Al paste used for making screen printed contacts to B emitter is investigated. Five different Ag/Al pastes with varying Al content below <;5% Al were formulated. It is found that contact resistance decreased monotonically with the increase in Al content. In addition, a slight decrease in effective sheet resistance of boron emitter was observed for higher Al content paste, possibly due to some Al incorporation underneath the grid during contact formation. These two effects resulted in an increase in fill factor for higher Al content paste. However, increased Al content also resulted in wider grid line and lower aspect ratio, resulting in a slight decrease in Jsc and increase in grid line resistance. In addition, higher Al tends to increase emitter saturation current density (J0e) and degrade junction quality. The competition between the fill factor and Jsc led to an optimum Al content, which produced basic n-type front junction cells with an average cell efficiency of 19.8% in this study.

n-Type CZ Substrate

Front metal contact induced recombination and resistance are major efficiency limiting factors of large-area screen-printed n-type front junction Si solar cells with homogeneous emitter and tunnel oxide passivated back contact (TOPCON). This paper shows the development of a selective boron emitter (p+/p++) formed by a screen-printed resist masking and wet chemical etch-back process, which first grows a porous Si layer and subsequently removes it. Various wet-chemical solutions for forming porous Si layer are investigated. An industrial compatible process with sodium nitrite (NaNO2) catalyst is developed to uniformly etch-back the ∼47 Ω/◻ atmospheric pressure chemical vapor deposited heavily doped boron emitter to ∼135 Ω/◻ by growing a 320 nm porous Si layer within 3 min and subsequently removing it. After etching back, the boron emitter was subjected to a thermal oxidation to lower the surface concentration and the emitter saturation current density J0e. Various etched-back emitters were evaluated by meas...

Effect of Al content on the performance of Ag/Al screen printed N-type Si solar cells

This chapter aims to provide students/workers in the field of photovoltaics with the valuable information and knowledge needed to understand the physics and operation of high‐efficiency front junction n‐type crystalline silicon solar cells. The surface recombination and passivation mechanisms, and several promising passivation schemes for front and back cell surfaces, are addressed and reviewed. The advanced cell structures and their fabrication schemes to achieve higher efficiency are described and discussed, including selective emitter on the front and locally doped back surface filed or carrier selective rear contact composed of tunnel oxide and phosphorus‐doped polycrystalline silicon thin film. These advanced cell design features have become highly active areas of investigations in the photovoltaic industry for next‐generation production cells.