Making Perovskite Solar Cells More Stable

Researchers at  Xi’an Jiaotong University and Uppsala University have created a new film that sticks better to perovskite solar cells, making them more stable and efficient.

Photovoltaic (PV) technologies have become increasingly common in recent years, aiding efforts to reduce greenhouse gas emissions. While most solar cells are silicon-based, alternative materials like perovskites are gaining attention for their potential to create cheaper solar cells with high power conversion efficiencies. However, perovskite solar cells (PSCs) are less stable than their silicon counterparts, with performance often declining under high temperatures and fluctuating environmental conditions. A key challenge lies in their reliance on hole-selective self-assembled monolayers (SAMs). These thin molecular films attract positive charge carriers but often fail to adhere well to the cell surface, contributing to thermal instability.

Researchers from Xi’an Jiaotong University, Uppsala University, and other institutions have developed a self-assembled bilayer film to address this. Their study shows that this bilayer structure adheres better to PSCs, improving their thermal stability and performance.

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The newly designed self-assembled bilayer improves conventional SAMs by adding an organic compound triphenylamine upper layer. This layer forms covalent bonds with the phosphonic acid-based SAM, creating a polymerized network.

The polymerized network, formed through Friedel–Crafts alkylation, demonstrated resistance to thermal degradation at temperatures up to 100 °C for 200 hours. The upper layer’s face-on orientation enhanced adhesion to perovskite surfaces, increasing the adhesion energy by 1.7 times compared to the standard SAM–perovskite interface.

In tests, the bilayer adhered better to perovskite surfaces than traditional monolayer SAMs. The production method is versatile, allowing it to be applied to various SAM-forming molecules and alkylating agents.

When applied to inverted PSCs, the bilayer improved performance, achieving high power-conversion efficiencies while reducing efficiency loss over time. The bilayer also enhanced stability under high-temperature conditions. The devices achieved power conversion efficiencies exceeding 26%. They demonstrated less than 4% and 3% efficiency loss after 2,000 hours of damp heat exposure (85 °C and 85% relative humidity) and over 1,200 thermal cycles between −40 °C and 85 °C, meeting international temperature stability standards.

This approach could pave the way for developing other self-assembled bilayer films to improve PSC stability. Such advancements could accelerate the adoption of perovskite-based photovoltaics.

Reference: Bitao Dong et al, Self-assembled bilayer for perovskite solar cells with improved tolerance against thermal stresses, Nature Energy (2025). DOI: 10.1038/s41560-024-01689-2.