Halide perovskites are a family of materials that have shown potential for high performance and low production costs in solar cells. In particular, cesium lead iodide (CsPbI3) is one of the perovskites used for photovoltaic applications. It has been extensively studied in recent years due to its excellent photovoltaic performance and thermal stability, especially the tetragonal phase in which the highest efficiency (~20%) has been achieved compared to the cubic and orthorhombic phases [1]. In perovskite solar cells, there is a commonly observed increase in device performance, especially in the open-circuit voltage, after subsequent current density–voltage (J–V) measurements under 1 sun illumination. This phenomenon is described as a light-soaking effect [2]. Various interpretations of the underlying physical mechanics have been proposed, and recent works attribute light-soaking to ion migration [3]. Typically, ion migration is associated with negative impacts such as hysteresis or device degradation, and considerable efforts have been made to suppress ionic movement in perovskite solar cells. However, this work demonstrates that ionic migration can actually have a positive impact on the performance of perovskite solar cells. The positive impact can be explained by ions migrating and subsequent trapping at the CsPbI3/electron transport layer interface, which induces band bending, thus increasing the built-in potential, the open-circuit voltage of the device, and its overall efficiency. 

References

[2] S.Tan, C. Tan, Y. Cui, B. Yu, Y. Li, H. Wu, J. Shi, Y. Luo, D. Li, Q. Meng Adv. Mater., 2023, 35, 2301879

[2] C. Yang; Z. Hu; C. Gao; Y. Wang; H. Zhang; X. Zhou; Y. Zhu J. Phys. Chem. C, 2020, 124 (3), 1851–1860.

[3] J.A., Kress; C. Quarti; A. Qingzhi; S. Bitton; N. Tessler; D. Beljonne; J. Vaynzof ACS Energy Lett. 2022, 7(10): 3302–3310.