Implications of Electron Transport Layer and Back Metal Contact Variations in Tin-Lead Perovskite Solar Cells Assessed by Spectroscopic Ellipsometry and External Quantum Efficiency

Alexander Bordovalos; Biwas Subedi; Lei Chen; Zhaoning Song; Yanfa Yan; Nikolas J Podraza

doi:10.1021/acsami.3c01849

Implications of Electron Transport Layer and Back Metal Contact Variations in Tin-Lead Perovskite Solar Cells Assessed by Spectroscopic Ellipsometry and External Quantum Efficiency

ACS Appl Mater Interfaces. 2023 Apr 19;15(15):19730-19740. doi: 10.1021/acsami.3c01849. Epub 2023 Apr 6.

Authors

Alexander Bordovalos¹, Biwas Subedi¹, Lei Chen¹, Zhaoning Song¹, Yanfa Yan¹, Nikolas J Podraza¹

Affiliation

¹ Department of Physics and Astronomy & Wright Center for Photovoltaics Innovation and Commercialization, University of Toledo, Toledo, Ohio 43606, United States.

PMID: 37022937
DOI: 10.1021/acsami.3c01849

Abstract

The structural and optical properties of hybrid organic-inorganic metal halide perovskite solar cells are measured by spectroscopic ellipsometry to reveal an optically distinct interfacial layer among the back contact metal, charge transport, and absorber layers. Understanding how this interfacial layer impacts performance is essential for developing higher performing solar cells. This interfacial layer is modeled by Bruggeman effective medium approximations (EMAs) to contain perovskite, C₆₀, BCP, and metal. External quantum efficiency (EQE) simulations that consider scattering, electronic losses, and the formation of nonparallel interfaces are created with input derived from ellipsometry structural-optical models and compared with experimental EQE to estimate optical losses. This nonplanar interface causes optical losses in short circuit current density (J_SC) of up to 1.2 mA cm^-2. A study of glass/C₆₀/SnO₂/Ag or Cu and glass/C₆₀/BCP/Ag film stacks shows that C₆₀ and BCP mix, but replacing BCP with SnO₂ can prevent mixing between the ETLs to prevent contact between C₆₀ and back contact metal and enable the formation of a planar interface between ETLs and back contact metals.

Keywords: external quantum efficiency modeling; interfacial layers; optical and electronic losses; optical properties; perovskite solar cells; spectroscopic ellipsometry.