Insulator Materials for Interface Passivation of Cu(In,Ga)Se2 Thin Films

In this work, metal–insulator–semiconductor structures were fabricated in order to study different types of insulators, namely, aluminum oxide (Al
₂
O
₃
), silicon nitride, and silicon oxide (SiO
_x
) to be used as passivation layers in Cu(In,Ga)Se
₂
(CIGS) thin-film solar cells. The investigated stacks consisted of SLG/Mo/CIGS/insulator/Al. Raman scattering and photoluminescence measurements were done to verify the insulator deposition influence on the CIGS surface. In order to study the electrical properties of the CIGS–insulator interface, capacitance versus conductance and voltage (
C–G–V
) measurements were done to estimate the number and polarity of fixed insulator charges (
Q_f
). The density of interface defects (
D
_it
) was estimated from capacitance versus conductance and frequency (
C–G–f
) measurements. This study evidences that the deposition of the insulators at high temperatures (300 °C) and the use of a sputtering technique cause surface modification on the CIGS surface. We found that, by varying the SiO
_x
deposition parameters, it is possible to have opposite charges inside the insulator, which would allow its use in different device architectures. The material with lower
D
_it
values was Al
₂
O
₃
when deposited by sputtering.