ALD ZnSnO buffer layer for enhancing heterojunction interface quality of CZTS solar cells

Kesterite $Cu_{2}ZnSnS_{4}$(CZTS) solar cells have emerged as a promising candidate for scalable thin-film solar cells development, mainly due to its outstanding performance and compatibility with CuInGaSe
₂
and CdTe solar cells while only consisting of earth-abundant and non-toxic constituents. Here we present a method to address the relative low $V_{OC}$of CZTS solar cells by applying atomic layer deposited $Zn{}_{1-x}Sn_{x}O$(ZTO) as a Cd-free buffer layer. X-ray photoelectron spectroscopy measurement is implemented to study the band alignment at the CZTS $/ZTO$ hetero-interface. It shows that the favorable conduction band alignment of CZTS $/ZTO$ resulted in increasing $V_{OC}$by up to 10 %. By optimizing the treatment of CZTS absorber before ZTO deposition, we finally obtained an efficiency of 9.3 % which is the highest efficiency so far reported for Cd- free pure sulphide CZTS solar cells to the best of our knowledge.