Buffer Layer Point Contacts for CIGS Solar Cells Using Nanosphere Lithography and Atomic Layer Deposition

Point contacts provide an interesting approach for reducing the buffer layer/Cu(In,Ga)Se
₂
interface recombination that typically limits Cu(In,Ga)Se
₂
solar cell performance when nontoxic alternatives to CdS buffer layers are used. In this study, we implement a scheme to create a point contact buffer layer on Cu(In,Ga)Se
₂
solar cells using a combination of atomic layer deposition and nanosphere lithography. While we showcase these buffer layers using Al
₂
O
₃
as the passivating material, ZnO as the conductive material, and a silica nanosphere size of 310 nm in diameter, this scheme is general and could readily be applied for other materials and other sphere sizes. The resulting solar cells with Al
₂
O
₃
and ZnO point contact buffer layers demonstrate successful application of this scheme, yielding a higher conversion efficiency (6.58 ± 0.58%) than either of the binary buffer layers Al
₂
O
₃
(0%) and ZnO (5.15 ± 0.57%). The improvement over ZnO is mainly due to an increased open circuit voltage, which is an indication of a reduced surface recombination.