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

Abstract

Point contacts provide an interesting approach for reducing the buffer layer/Cu(In,Ga)Se2 interface recombination that typically limits Cu(In,Ga)Se2 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 Al2O3 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 Al2O3 and ZnO point contact buffer layers demonstrate successful application of this scheme, yielding a higher conversion efficiency ( $6.58\,\pm \,0.58\% $ ) than either of the binary buffer layers Al2O3 (0%) and ZnO ( $5.15\,\pm \,0.57\% $ ). The improvement over ZnO is mainly due to an increased open circuit voltage, which is an indication of a reduced surface recombination.