Abstract to NIPHO9

It was reported that the use of inorganic cations affects the long-term stability of perovskite solar cells (PSCs), which remains a major impediment for its industrial application¹. As a result, there have been several attempts to replace the organic cations with inorganic elements to improve the cells’ stability ²_’³ .CsPbI₃ is considered one of the most promising candidates to achieve a stable perovskite structure.

The perovskite’s dimensionality is determined by using a barrier molecule between the inorganic perovskite framework. The barrier molecule is too big to fit into the cage formed by the perovskite octahedrons and therefore, it creates confined inorganic perovskite layers. This low-dimensional perovskite creates a quantum-well structure, where the inorganic framework and the long organic molecules act as wells and barriers, respectively.

Unlike the three dimensional (3D) perovskite, the low-dimensional perovskite has shown promising stability, but it has a much lower power conversion efficiency. The relatively low efficiency of two-dimensional (2D) perovskite solar cells (PSCs) is mainly due to the barrier molecules, which could inhibit charge transport through the film. However, it is likely that combining the high efficiency of 3D perovskite with the enhanced stability of 2D perovskite could be an elegant way to achieve specific requirements from a photovoltaic solar cell⁴.

In this work we demonstrated how the black phase of CsPbI₃ can be stabilized when its dimensionality is reduced. Low-dimensional CsPbI₃ perovskites were fabricated using two different barrier molecules: linear and aromatic barrier molecules. XRD and SEM show the degradation process of these films, where the low-dimensional perovskite, using an aromatic barrier molecule, displays better stability than does the low-dimensional perovskite, using a linear barrier molecule. Both barrier molecules display enhanced photostability under continuous 1 sun illumination compared with 3D CsPbI₃ film, which degrades rapidly. However, the aromatic barrier molecule displays superior photostability compared with the linear barrier. Theoretical calculations explain this observation by the point and extended defects, which increase the time for degradation. Here, we have shown the potential of stabilizing the black phase of CsPbI₃, which provides the possibility to use it efficiently and stably in PV solar cells.