Screen-printed reflector pastes for back passivated crystalline silicon solar cells

Solar cell manufacturers across the world are working to find innovative ways to reduce cost per installed watt of photovoltaic energy generation in order to achieve grid parity. Some of these approaches involve the use of revolutionary cell architectures such as metal wrap-through (MWT) [1], PERC cells, local back surface field (BSF) [2] and selective emitter among others. Many of these new approaches call for development of special back Al pastes that can either fire-through passivation stacks such as Al₂O₃/SiNx [3] or form local BSF in laser opened vias. In other designs, the Al paste needs to act as a reflective surface below the SiNx layer, without firing through the dielectric layer (reflector paste). In this paper we discuss the requirements for reflector paste in back-passivated cell applications. The paper will also present the various attributes of these pastes such as non firethrough properties, adhesion to SiO₂, Al₂O₃ or SiNx passivation layers, excellent reflectance and low electrical resistance.