Halide perovskites: stability, interfaces, and internal dynamics

This section presents selected highlights from our research on halide perovskites.

Solution-processed halide perovskites have emerged as key materials for next-generation photovoltaics, owing to their strong optical absorption, high defect tolerance, and compatibility with low-temperature fabrication processes. However, their performance and long-term durability remain strongly influenced by complex internal phenomena, such as ionic dynamics, local thermal effects, and the critical role of interfaces.

Our research aims to understand and control these internal mechanisms by combining interfacial engineering with advanced diagnostic techniques, with the goal of improving both the performance and the operational stability of perovskite-based devices.

I. In situ access to internal dynamics and degradation mechanisms

One of recent works introduced an original in situ approach to directly probe inside functional perovskite solar cells under illumination. By integrating upconversion nanoparticles (UCNPs) at buried interfaces, we developed a nanoscale local thermometry technique enabling real-time monitoring of the temperature evolution at the perovskite/hole transport layer interface during accelerated ageing experiments.

This approach revealed the existence of distinct degradation regimes, arising from the competition between local heat accumulation and structural and optical transformations of the absorber material. These results provide new insight into the physical mechanisms governing device degradation and pave the way toward a more mechanistic understanding of perovskite solar cell stability.

Figure caption: (Left) Schematic of the device architecture and strategy for integrating upconversion nanoparticles (UCNPs) as nanothermometers at the buried perovskite/HTL interface; (Right) Evolution of the interfacial temperature during accelerated degradation under illumination. The measurements reveal competing mechanisms, including thermal accumulation and material decomposition, whose relative dominance depends on both the applied stress intensity and the perovskite composition.

Publication :
Nie, J. ; Zhang, D. ; Xiang, H. ; Pons, T. ; Aigouy, L. ; Chen, Z. Nanothermometry-Guided in Situ Decoding of Perovskite Solar Cell Degradation under Optical Stress. Nano Energy 2025, 144, 111405. https://doi.org/10.1016/j.nanoen.2025.111405.

Highlights for scientific and non-scientific public :
https://www.pepr-tase.fr/2025/12/05/temperature-perovskites/

II. Functional interfaces for enhanced operational stability

In parallel, we have investigated the role of interfaces as key initiation sites for instability processes in perovskite solar cells. In particular, we demonstrated that the controlled integration of colloidal carbon quantum dots (CQDs) at strategic interfaces enables the combination of efficient UV screening and downshifting with favorable modifications of the electronic interfaces. This multifunctional approach leads to a significant improvement in stability under UV illumination, without compromising photovoltaic performance.

These results highlight the interest of interfacial engineering strategies that act simultaneously on multiple optical and electronic levers.

Figure caption: (Left) Schematic of the perovskite solar cell architecture integrating fluorescent carbon quantum dots (CQDs) selectively deposited on different device surfaces and interfaces; (Right) Comparative evolution of the power conversion efficiency (PCE) of non-encapsulated perovskite solar cells with and without CQDs, for different integration configurations, under continuous UV illumination in air (RH ∼ 40%).

Publication :

Zhang, D. ; Hu, Z. ; Vlaic, S. ; Xin, C. ; Pons, S. ; Billot, L. ; Aigouy, L. ; Chen, Z. Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV. Small 2024, 20 (35), 2401505. https://doi.org/10.1002/smll.202401505.

III. Engineering of active layers and interfaces for high-performance and robust solar cells

Our earlier work focused on interface engineering in perovskite solar cells, with the aim of identifying and controlling the mechanisms limiting device performance and stability. We notably showed that residual phases such as PbI₂ at the perovskite/hole transport layer interface, often considered benign, can instead play a decisive role. Their controlled removal leads to a simultaneous improvement in photovoltaic efficiency and stability, underlining the importance of precise interfacial quality control.

Within the same interfacial engineering framework, we investigated the impact of nanostructured electron transport layers, in particular TiO₂ nanocolumn arrays. This approach modifies the optical management of the device by enhancing local electromagnetic field concentration and increasing ultraviolet absorption, while also improving charge transport properties. The integration of TiO₂ nanocolumns results in higher short-circuit current and power conversion efficiency, together with a marked improvement in storage stability (shelf life) of the solar cells, demonstrating the potential of nanostructured interfaces for enhancing the robustness of perovskite devices.

Figure caption: (a) Evolution of the power conversion efficiency over 100 h for non-encapsulated triple-cation perovskite solar cells CsMAFAPb(I_1-xBr_x)₃, whose active layer was treated with MAI (blue), FAI (orange), MABr (violet), or MACl (pink), compared with an untreated reference cell (green). Measurements were performed under continuous AM 1.5G illumination (100 mW cm^-2) in an inert atmosphere (Ar glovebox). The inset shows SEM images of the active layer before and after MAI treatment, illustrating the removal of excess interfacial PbI₂. (b) Left: SEM image of vertically aligned TiO₂ nanocolumns. Right: degradation behavior of triple-cation perovskite solar cells using either a planar or nanostructured (TiO₂ nanocolumn) electron transport layer. The inset shows an optical image of two devices fabricated on the same substrate after air ageing, without (left) and with (right) nanocolumns.

Publications :

Hu, Z. ; An, Q. ; Xiang, H. ; Aigouy, L. ; Sun, B. ; Vaynzof, Y. ; Chen, Z. Enhancing the Efficiency and Stability of Triple-Cation Perovskite Solar Cells by Eliminating Excess PbI₂ from the Perovskite/Hole Transport Layer Interface. ACS Appl Mater Interfaces 2020, 12 (49), 54824–54832. https://doi.org/10.1021/acsami.0c17258.

Hu, Z. ; García-Martín, J. M. ; Li, Y. ; Billot, L. ; Sun, B. ; Fresno, F. ; García-Martín, A. ; González, M. U. ; Aigouy, L. ; Chen, Z. TiO₂ Nanocolumn Arrays for More Efficient and Stable Perovskite Solar Cells. ACS Appl Mater Interfaces 2020, 12, 5979–5989. https://doi.org/10.1021/acsami.9b21628.