Light management in highly-textured perovskite solar cells: From full-device ellipsometry characterization to optical modelling for quantum efficiency optimization

• Published in: Solar energy materials and solar cells Vol. 230
• Main Authors: Ma, Chenxi, Zheng, Daming, Demaille, Dominique, Gallas, Bruno, Schwob, Catherine, Pauporté, Thierry, Coolen, Laurent
• Format: Journal Article
• Language: English
• Published: Elsevier 01.05.2021
• Subjects: Physics
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2021.111144

As perovskite solar cells (PSC) are now reaching high power conversion efficiencies, further performance improvement requires a fine management and harvesting optimization of light in the cells. These request an accurate understanding, characterization and modelling of the optical processes occurring within these complex, often textured, multi-layered systems. We consider here a typical methylammonium lead iodide (MAPI) solar cell built on a fluorine-doped tin oxide (FTO) electrode of high roughness. We used variable-angle spectroscopic ellipsometry (VASE) to design a one-dimensional (1D) optical model of the stacked layers describing the rough texture as layers of effective-medium index. While most previous reports on PSC optical models performed ellipsometry only on single layers of each material independently deposited on glass, our model was obtained by an extensive ellipsometric analysis of the full stratified PSC structure at each deposition step. We support the 1D model using data extracted from scanning electron microscopy, diffuse spectroscopy and photovoltaic efficiency measurements and compare its results with full 3D simulations. Although the 1D model is insufficient to describe scattering by the FTO plate alone, it gives an accurate description of the full device optical properties. By comparison with the experimental external quantum efficiency (EQE), we estimate the internal quantum efficiency (IQE) and the effect of the losses related to electron transfer. We finally discuss the optical losses mechanisms and possible strategies to improve light management and further increase PSC performances.