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

Year: 2017

Journal: IEEE J. Photovolt., Volume 7, JAN, page 322–328

Authors: Hultqvist, Adam; Sone, Takero; Bent, Stacey F.

Organizations: Center on Nanostructuring for Efficient Energy Conversion, Stanford University; U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0001060]; Marcus and Amalia Wallenberg Foundation through the Stig Hagstrom Stipend; Vice Provost for Under graduate Education at Stanford through the Chemical Engineering Summer Research Program

Keywords: Atomic layer deposition; buffer layer; Cu(In, Ga)Se-2 (CIGS) thin film solar cell; nanosphere lithography; point contacts

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 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 +/- 0.58%) than either of the binary buffer layers Al2O3 (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.