To enhance the thermal stability of perovskite solar cells (PSCs)
Several materials and strategies are being employed that address the key issues of ion migration, thermal stress, and degradation of organic components within the cells. The main materials and approaches include:
Polymer Additives and Encapsulation
- Polystyrene-co-polyacrylonitrile (SAN) Copolymer: Incorporating SAN into methylammonium lead iodide (MAPI) perovskite layers significantly suppresses the migration of organic cations (methylammonium, MA⁺), which is a major cause of thermal degradation. SAN creates an immiscible environment that limits MA⁺ out-diffusion and reduces ionic currents at the grain boundaries, thereby enhancing thermal stability at elevated temperatures (e.g., showing only 5–15% performance loss after 24 hours at 100 °C).
- Thermoplastic Additives such as Polyethylene Glycol (PEG) and Polyethylene Oxide (PEO): These crystalline polymers have been used to improve the thermal stability of perovskite films by stabilizing the crystal structure and inhibiting ion migration, although details were briefly noted without extensive elaboration in the available context.
Engineering of Hole Transport Layers (HTLs)
- Polymeric Hole Transport Layers Based on TPT-T (MB/C6): Synthesized polymers with specific side chains (e.g., 2-methylbutyl and hexyl groups) show improved thermal stability compared to the commonly used spiro-OMeTAD. These polymers exhibit no thermal transitions below 200 °C, preventing cracking and preserving hole mobility under thermal stress (tested at 65 °C), thereby improving stability of the perovskite solar cells.
- Avoidance of Spiro-OMeTAD Additives That Crystallize at Elevated Temperatures: Spiro-OMeTAD with additives tends to crystallize around 85 °C, causing degradation of hole mobility and device performance. Replacing spiro-OMeTAD with more thermally robust HTLs like NiO or the aforementioned polymers improves thermal endurance of PSCs.
Crystallinity and Buffer Layers
- Improving Crystalline Quality of Perovskite Films: Enhancing the crystal quality reduces defects and ion migration pathways, making the perovskite layer more resilient to thermal cycling.
- Use of Suitable Buffer Layers: Buffer layers can mitigate thermal stress caused by differences in thermal expansion and contraction between dissimilar adjacent materials. This reduces mechanical degradation and maintains good interlayer contact during temperature fluctuations experienced in outdoor conditions (from -40 °C to +100 °C or beyond).
Summary Table
| Material / Strategy | Role in Enhancing Thermal Stability | Key Benefits |
|---|---|---|
| Polystyrene-co-polyacrylonitrile (SAN) | Suppresses organic cation (MA⁺) migration in perovskite layer | Reduces ionic currents, limits degradation at 100 °C |
| Polyethylene Glycol (PEG) & Polyethylene Oxide (PEO) | Crystalline thermoplastic additives stabilizing precursor | Improved film stability under heat |
| TPT-based conjugated polymer HTLs | Thermally robust hole transport layers without low-temp transitions | Maintains hole mobility, prevents cracking at 65 °C |
| NiO HTLs | Stable inorganic hole transport layer | Improved PCE retention after thermal cycling |
| Enhanced perovskite crystallinity | Improves structural integrity | Mitigates ion migration and thermal degradation |
| Suitable buffer layers | Mitigates interlayer thermal stress | Maintains layer contact, reduces mechanical failure |
In essence, enhancing the thermal stability of perovskite solar cells involves a combination of polymer additives within the perovskite itself to reduce ion migration, the use of stable polymeric or inorganic hole transport layers that resist thermal transitions and degradation, and structural improvements such as better crystallinity and buffer layers to manage thermal stress between different materials. These strategies collectively contribute to longer-term operational stability of perovskite solar cells under real-world thermal cycling conditions.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/what-materials-are-being-used-to-enhance-the-thermal-stability-of-perovskite-solar-cells/
