Fine line printed silicon solar cells exceeding 20% efficiency



Silicon solar cells with passivated rear side and laser-fired contacts were produced on float zone material. The front side contacts are built up in two steps, seed and plate. The seed layer is printed using an aerosol jet printer and a silver ink. After firing this seed layer through the silicon nitride layer, the conductive layer is grown by light induced plating. The contact formation is studied on different emitter sheet resistances, 55 Ω/sq, 70 Ω/sq, and on 110 Ω/sq. These emitters are passivated with a PECVD silicon nitride layer which also acts as an anti-reflection coating. Even on the 110 Ω/sq emitters it was possible to reach a fill factor of 80·1%. The electrical properties i.e., the contact resistance of the front side contacts are studied by transfer length model (TLM) measurements. On a cell area of 4 cm2 and emitter sheet resistance of 110 Ω/sq, a record efficiency of 20·3% was achieved. Excellent open-circuit voltage (Voc) and short-circuit current (jsc) values of 661 mV and 38·4 mA/cm2 were obtained due to the low recombination in the 110 Ω/sq emitter and at the passivated rear surface. These results show impressively that it is possible to contact emitter profiles with a very high efficiency potential using optimized printing technologies. Copyright © 2008 John Wiley & Sons, Ltd.