Impact of Texture Roughness on the Front-Side Metallization of Stencil-Printed Silicon Solar Cells

Abstract

Realizing narrow contact fingers with low lateral resistance is a major goal for the front-side metallization of silicon solar cells. The formation of screen-or stencil-printed contact fingers is governed by a variety of influencing factors. One of these factors is the surface roughness of the textured silicon wafer. However, only a few investigations have been carried out to investigate this impact in detail. In this study, the influence of arithmetical mean roughness R a of four differently textured wafer surfaces on contact finger geometry and lateral finger resistance, as well as optical and electrical losses, has been investigated. It will be shown that texture roughness has a considerable impact on the properties of the front-side grid. Narrower contact fingers could be realized on the smoothest texture, leading to a current density gain of Δj sc = +0.27 mA/cm 2 . On the other hand, increasing texture roughness has affected the amount of transferred paste and, thus, has led to a lower lateral finger resistance R L . Thus, contact fingers on the roughest texture have benefited from a fill factor gain of ΔFF = +0.24 % ab s . A sensitivity analysis of both impacts has shown that the current density gain has overcompensated the fill factor loss. Thus, textures with a small roughness are beneficial with respect to the formation and electrical properties of stencil-printed front-side grids.

The Link between Ag‐Paste Rheology and Screen‐Printed Solar Cell Metallization

“…All wafers had an alkaline texture made out of square‐based pyramids with an angle of 50°–52° and a size in the range of 0.5–1.1 µm. [ 42,43 ] Directly after the printing step, all wafers were dried for 90 s at a temperature of T = 220 °C. Afterward, paste sintering was performed through an industrial firing process with a peak temperature of T = 835 °C for 60 s. More information on the firing profile can be found in ref.…”

High‐Throughput Indirect Gravure Printing Applied to Low‐Temperature Metallization of Silicon‐Based High‐Efficiency Solar Cells

“…The solar cell wafers' impact on the measurement and potential finger interruptions were neglected and r f was calculated. [43] r f ¼ R bb  n finger  p bb À1…”

Printing technologies for silicon solar cell metallization: A comprehensive review

“…Several parameters affect the effectivity of the edge sealing and thus the extent of paste spreading along the channel edges. The morphology of the surface (roughness of the texture) obviously has a strong impact on the sealing quality of the channels and thus paste spreading 260,261 . Texturing the wafer surface with small random pyramids or using new approaches like plasma etching 262 can help to increase the quality of the metallization without deteriorating the optical properties.…”

“…The morphology of the surface (roughness of the texture) obviously has a strong impact on the sealing quality of the channels and thus paste spreading. 260,261 Texturing the wafer surface with small random pyramids or using new approaches like plasma etching 262 can help to increase the quality of the metallization without deteriorating the optical properties. The effectivity of the edge sealing is further influenced by material properties (softness) and surface roughness (typically specified with the R z value) of the emulsion and the printing parameters-predominately the squeegee pressure.…”