Front-side Ag contacts enabling superior recombination and fine-line performance

Abstract

The standard silicon solar cell process continues on an evolutionary improvement path. High quality monocrystalline cells are now able to reach 19.2 % conversion efficiencies in industrial production. A key enabler for these high efficiencies has been the front-side Ag contact. This paper will discuss recent developments in this technology on two parallel fronts: reduced recombination and fine line printing. Front-side Ag can reduce solar cell recombination currents directly through reduced metal contact saturation current. In addition front-side Ag can indirectly lower recombination through improved contact formation to low saturation current emitters (lightly doped emitters, or LDE). Through improvements in the frit chemistry a superior recombination performance was enabled, yielding a 3 mV Voc gain and 0.1 % efficiency gain over the control. Improvements in the Ag particle dimensions and paste rheology reduced the optimum finger width approximately 10 μm, increasing Jsc by 0.3 mA/cm2 improving the efficiency gain another 0.1 % over the incumbent technology. In net we are able to demonstrate a next generation front-side Ag paste that can improve efficiency 0.2 %, from 18.8 % to 19.0 %.