Enhanced Light Trapping in Thin Silicon Solar Cells using Effectively Transparent Contacts (ETCs)

We report on the light trapping properties of densely spaced microscale triangular cross-section effectively transparent contacts (ETCs). Optical simulations of thin silicon with closely spaced ETCs were performed and the absorption within the silicon was determined. We found that with a metal coverage of 62.5% the short circuit current density would only be decreased by 0.25%. Such low value of parasitic reflection and transmission is obtained due to the excellent reflection properties of silver microstructures. In the interval 700 nm-1100 nm the short circuit current density is even enhanced by around 1 mA/cm
²
compared to a structure without any metal contact. This results from nearly loss free in-coupling in combination with internal reflection at the bottom of the metal lines which increases the path length of light. These results are particularly interesting for 4-terminal silicon tandem devices as the bottom cell only receives the spectrum between around 850 nm and 1100 nm.