An Oxford researcher has found that transparent conductive electrodes can reduce the efficiency of perovskite-silicon tandem solar cells by more than 2%, with losses related to electrical resistance, optical effects and geometric trade-offs. Using a unified optical-electrical model, the scientist showed how careful optimization of TCE stacks, coatings and cell design is critical to closing the gap to the 37%-38% efficiency limit.
A University of Oxford researcher has investigated the impact of transparent conductive electrodes (TCEs) on the performance of perovskite-silicon tandem solar cells and found that they can significantly reduce the device’s efficiency.
It is expected that TCEs will play a decisive role in determining whether tandem cells can close the remaining gap between the current efficiency of 34% and the expected efficiency limit of 37%-38%.
“Our study provides the first framework to quantify these losses in tandem PV, showing how the performance of even the best tandem designs can drop by more than 2.5% due to TCE-related effects,” the study’s lead author Sebastian Bonilla told pv magazine. “These insights are crucial for manufacturers and researchers who want to scale tandems from laboratory cells to commercial modules.”
“The use of transparent conductive electrodes (TCEs), While this is often assumed to be ideal, it can introduce electrical resistance and optical losses that significantly reduce the efficiency of tandem modules in practice,” he continued.Their practical efforts still encounter underappreciated barriers.”
In the newspaper “The impact of transparent conductive electrodes on the efficiency of tandem solar cells”, published in JouleBonilla explained that current optical modeling is unable to quantify the lateral resistance of TCEs, especially in bifacial or front-illuminated configurations. Furthermore, the geometric interdependence between TCE plate resistance, finger spacing, and metal shading creates trade-offs that fundamentally limit power but are rarely reflected in practical efficiency calculations.
With this in mind, Bonilla outlined a unified optical-electrical model that takes these factors into account in two-terminal perovskite-silicon tandem solar cell designs. Various TCE stacks were considered to assess potential transmission losses, while anti-reflective coatings, sputtered buffer layers and optimized finger spacing were also included.
Using PySpice, a Python-based simulation framework for electronic circuits, the scientist implemented a circuit model that enables flexible parametric measurements of material properties, including saturation current densities, recombination diode parameters and resistive losses. “This modeling is valid for two solar absorbers, but I apply it to perovskite-silicon tandem cells because of their maturity and commercial relevance,” says Bonilla.
The analysis showed that tandem devices with only one TCE can suffer an efficiency loss of up to 2%. However, tandem cells usually use center and rear TCEs, which further reduce performance. These losses, according to Bonilla, are consistent with experimental findings showing that small adjustments in indium tin oxide (ITO) deposition, anti-reflective coatings, or atomic-deposited barrier layers directly lead to measurable performance improvements in state-of-the-art tandem cells.
“These insights are crucial for manufacturers and researchers who want to scale tandems from laboratory cells to commercial modules,” Bonilla concludes. “The findings also highlight opportunities for material innovation and design co-optimization to ensure future high-efficiency tandems reach their full potential in real-world applications.”
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