The Institute for Solar Energy Research Hamelin (ISFH) increases the conversion efficiency of industrial p-type silicon solar cells with screen-printed metal contacts from today's typical 17.5% to 19.5% to a record value of 21.2%, using leading-edge front-side metallization pastes supplied by the Photovoltaics Business Unit of Heraeus Precious Metals.

21.2% is the highest efficiency reported so far for industry typical silicon solar cells using screen-printed metal contacts. The measurements were confirmed by the independent institute Fraunhofer ISE CalLab.

A combination of different technologies enabled this great result on an industrial PERC solar cell. As opposed to conventional solar cells, PERC cells have a passivated rear-side, which increases the amount of energy captured from the cell. ISFH's cell design incorporates a narrow front-side grid design using a dual printing process and an advanced five busbar design.

This special layout enables the reduction of finger line widths to 46 micrometre, which decreases shadowing losses and serial resistance. The narrower finger lines were printed with an industry-leading front-side silver metallization paste of Heraeus that processes a high fill factor and low series resistance. The busbars were printed using Heraeus' newest low activity paste.

This paste does not fire through the passivation layer, which results in an additional boost in Voc. The excellent properties of both pastes and the finely tuned process parameters have contributed to this great result.

"A 21.2% conversion efficiency for a PERC cell using standard production equipment is a true breakthrough. With the excellent processing knowledge and solar cell expertise of the ISFH, the front-side silver-pastes of Heraeus unfolded their cells' peak performance," states Dr. Weiming Zhang, Vice President of Technology of the Photovoltaics Business Unit.

"Cooperation with partners within the PV industry such as the ISFH is essential for us. It's an ideal platform to exchange state-of-the-art knowledge in cell technology and processing know-how for advancing solar energy."