High-efficient Cd-free CZTS solar cells achieved by nanoscale atomic layer deposited aluminium oxide

Kesterite Cu
₂
ZnSnS
₄
(CZTS) solar cells are considered as the promising alternative candidate for thin film solar cells, but still being hampered by the relative low V
_OC.
Here, we propose a heterojunction modification strategy by applying atomic layer deposited aluminium oxide (Al
₂
O
₃
) as a passivation layer. Through post-treatment of CZTS absorber by nanoscale ALD Al
₂
O
₃
, the effective lifetime of the minority carrier at the heterojunction improved, indicating a better passivation effects from nanoscale alumina. With a significant gain of Voc by 50 mV, we achieved a device efficiency of 9.9 %, the highest efficiency ever reported for Cd-free CZTS solar cells.