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 (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
_0e
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
_0e
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.