Selective Isolation of Surface Grain Boundaries by Oxide Dielectrics Improves Cd(Se,Te) Device Performance

Sartor, B. Edward; Muzzio, Ryan; Jiang, Chun-Sheng; Lee, Chungho; Perkins, Craig L.; Taylor, André D.; Reese, Matthew O.

doi:10.1021/acsami.4c16902

Title: Selective Isolation of Surface Grain Boundaries by Oxide Dielectrics Improves Cd(Se,Te) Device Performance

Journal Article · 23 January 2025 · ACS Applied Materials and Interfaces

DOI: https://doi.org/10.1021/acsami.4c16902 · OSTI ID:2506831

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National Renewable Energy Laboratory (NREL), Golden, CO (United States)
First Solar, Santa Clara, CA (United States)
New York University, Brooklyn, NY (United States)

Cd(Se,Te) photovoltaics (PV) are the most widely deployed thin-film solar technology globally, yet continued efficiency improvements are stymied by challenges at the device hole contacts. The inclusion of solution-processed oxide layers such as AlGaO_x in the contact stack has yielded improved device open-circuit voltages (V_OC) and fill factors (FF). However, contradictory mechanisms by which these layers improve the device properties have been proposed by the research community. We demonstrate in this work that an underappreciated property of such spin-coated layers is the preferential deposition at grain boundaries, a process that isolates the grain boundaries during contact metallization. The effects of grain-boundary isolation are probed by varying the coverage of solution-processed AlGaO_x “barrier” layers on the Cd(Se,Te) surface, quantified by scanning Auger microscopy. Examining coverage-dependent V_OC and FF, it was observed that isolating the grain boundaries during metallization is sufficient to prevent damage to the absorber that occurs in devices lacking a barrier layer, while additional coverage contributes to the increased series resistance. Such an effect is agnostic to the material used as a barrier layer, as long as the material does not itself damage the absorber. Spin-coated SiO_x was used in place of AlGaO_x for an equally beneficial effect. This grain-boundary isolation phenomenon is also observed during Mo deposition and in absorbers that have been contacted with a nitrogen-doped ZnTe layer. The mechanisms by which metallization may degrade the absorber are discussed, as are contact design strategies leveraging barrier layers, which may lead to improved device efficiencies.

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Research Organization:: National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Organization:: USDOE; USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: AC36-08GO28308

OSTI ID:: 2506831

Journal Information:: ACS Applied Materials and Interfaces, Journal Name: ACS Applied Materials and Interfaces Journal Issue: 5 Vol. 17; ISSN 1944-8244

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CdTe
adsorption
contacts
deposition
grain boundaries
layers
metallization
oxides
photovoltaics
solution-processing

Title: Selective Isolation of Surface Grain Boundaries by Oxide Dielectrics Improves Cd(Se,Te) Device Performance

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