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Amorphous tin-gallium oxide buffer layers in (Ag,Cu)(In,Ga)Se2 solar cells

DOI: 10.1016/j.solmat.2020.110647 DOI Help

Authors: F. Larsson (Uppsala University) , J. Keller (Uppsala University) , J. Olsson (Uppsala University) , O. Donzel-Gargand (Uppsala University) , N. M. Martin (Uppsala University) , M. Edoff (Uppsala University) , T. Torndahl (Uppsala University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Solar Energy Materials And Solar Cells , VOL 215

State: Published (Approved)
Published: September 2020
Diamond Proposal Number(s): 21742

Open Access Open Access

Abstract: Amorphous tin-gallium oxide (a-SGO) grown with atomic layer deposition was evaluated as a buffer layer in (Ag,Cu)(In,Ga)Se2 thin-film solar cells in search for a new material that is compatible with a variety of absorber band gaps. Hard and soft X-ray photoelectron spectroscopy on absorber/a-SGO stacks combined with J–V characterization of solar cells that were fabricated, showed that the conduction band alignment at the absorber/a-SGO interface can be tuned by varying the cation composition and/or growth temperature. Here, the surface band gap was 1.1 eV for the absorber. However, optical band gap data for a-SGO indicate that a suitable conduction band alignment can most likely be achieved even for wider absorber band gaps relevant for tandem top cells. A best efficiency of 17.0% was achieved for (Ag,Cu)(In,Ga)Se2/a-SGO devices, compared to η = 18.6% for the best corresponding CdS reference. Lower fill factor and open-circuit voltage values were responsible for lower cell efficiencies. The reduced fill factor is explained by a larger series resistance, seemingly related to interface properties, which are yet to be optimized. Some layer constellations resulted in degradation in fill factor during light soaking as well. This may partly be explained by light-induced changes in the electrical properties of a-SGO, according to analysis of Al/SGO/n-Si metal-oxide-semiconductor capacitors that were fabricated and characterized with J–V and C–V. Moreover, the introduction of a 1 nm thick Ga2O3 interlayer between the absorber and a-SGO improved the open-circuit voltage, which further indicates that the absorber/a-SGO interface can be improved.

Journal Keywords: CIGS; ACIGS; Buffer layers; Atomic layer deposition; Band gap engineering; Interfaces

Diamond Keywords: Photovoltaics; Semiconductors

Subject Areas: Materials, Physics, Energy

Instruments: I09-Surface and Interface Structural Analysis

Added On: 23/06/2020 15:31


Discipline Tags:

Surfaces Earth Sciences & Environment Sustainable Energy Systems Energy Physics Climate Change Energy Materials Materials Science interfaces and thin films

Technical Tags:

Spectroscopy X-ray Photoelectron Spectroscopy (XPS) Hard X-ray Photoelectron Spectroscopy (HAXPES)