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

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/SiN_x stacks, where the silicon nitride (SiN_x) layer is deposited by PECVD. While the a-Si passivation of the Al-p⁺ emitter results in an emitter saturation current density J_0e of 246 fA/cm², the Al₂O₃/SiN_x double layers result in emitter saturation current densities as low as 160 fA/cm², which is the lowest J_0e reported so far for screen-printed Al-doped p⁺ emitters. Moreover, the Al₂O₃ as well as the Al₂O₃/SiN_x 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.