The ALU+ concept: N-type silicon solar cells with surface-passivated screen-printed aluminum-alloyed rear emitter

Abstract

Aluminum-doped p-type (Al- p+) silicon emitters fabricated by means of screen-printing and firing are effectively passivated by plasma-enhanced chemical-vapor deposited (PECVD) amorphous silicon (a-Si) and atomic-layer-deposited (ALD) aluminum oxide (Al2O3) as well as Al2O3/SiNx stacks, where the silicon nitride (SiNx) layer is deposited by PECVD. While the a-Si passivation of the Al-p+ emitter results in an emitter saturation current density J0e of 246 fA/cm2, the Al 2O3/SiNx double layers result in emitter saturation current densities as low as 160 fA/cm2, which is the lowest J0e reported so far for screen-printed Al-doped p+ emitters. Moreover, the Al2O3 as well as the Al 2O3SiNx stacks show an excellent stability during firing in a conveyor belt furnace at 900 °C. We implement our newly developed passivated Al-p+ emitter into an n+np + solar cell structure, the so-called ALU+cell. An independently confirmed conversion efficiency of 20% is achieved on an aperture cell area of 4 cm2, clearly demonstrating the high-efficiency potential of our ALU+ cell concept. © 2006 IEEE.