Growth of amorphous Zn–Sn–O thin films by RF sputtering for buffer layers of CuInSe2 and SnS solar cells

Abstract

We propose using amorphous Zn–Sn–O (α-ZTO) deposited by RF sputtering as an alternative n-type buffer layer for Cu(In,Ga)Se2 and SnS solar cells. The order of the carrier density, n, is increased from the order of 1015 to 1017cm−1 as the Sn/(Sn+Zn) atomic ratio increases from 0.29 to 0.40. On the other hand, the order of n decreased from 1017 to 1011cm−1 as the oxygen partial pressure increased from 0 to 10%. Further, for the α-ZTO film with the Sn/(Sn+Zn) atomic ratio at 0.38 and the oxygen partial pressure at 0%, valence band discontinuities of α-ZTO/CuInSe2 and α-ZTO/SnS were determined using photoelectron yield spectroscopy measurements. The band discontinuities of each of these interfaces form a spike structure in the conduction band offset, which enables a high-performance solar cell to be obtained.