The ${\bf ALU}^{+}$ Concept: $N$-Type Silicon Solar Cells With Surface-Passivated Screen-Printed Aluminum-Alloyed Rear Emitter

Robert Bock,Bram Hoex,Jan Schmidt,Susanne Mau,Rolf Brendel

doi:10.1109/ted.2010.2050953

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 (Al 2 O 3 ) as well as Al 2 O 3 /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 0 e of 246 fA/cm 2 , the Al 2 O 3 /SiN x double layers result in emitter saturation current densities as low as 160 fA/cm 2 , which is the lowest J 0 e reported so far for screen-printed Al-doped p + emitters. Moreover, the Al 2 O 3 as well as the Al 2 O 3 /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 cm 2 , clearly demonstrating the high-efficiency potential of our ALU + cell concept.

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