Perovskite solar cells are among the most promising and rapidly advancing solar cell technologies. Over the past decade, they have undergone significant performance improvements. By adjusting the composition of the perovskite layer, it is possible to optimize its electrochemical properties to achieve maximum efficiency. However, the primary drawback of perovskite solar cells is their sensitivity to moisture and oxygen, which can lead to the degradation of the perovskite layer and the formation of defects in its crystalline structure. These defects can also occur during the crystallization process, leading to a decrease in the longevity and efficiency of the final device [1,2].
Charge-transporting materials are crucial in determining the effectiveness and stability of perovskite solar cells. The presence of incompatible functional groups or electrochemically unstable compounds can negatively impact device performance. However, certain functional groups have the opposite effect—they can passivate existing defects in the perovskite layer and prevent the formation of new imperfections. One of the most effective functional groups for passivating the perovskite layer is the phosphine oxide fragment, which easily coordinates with free lead ions in the crystal. Such passivating compounds are often used to form interlayers, as they typically exhibit poor electron-transporting properties [3].
Currently, the most commonly used electron-transporting materials are fullerenes and their modified derivatives, such as PC\(_{61}\)BM and PC\(_{71}\)BM. These compounds possess excellent electrochemical properties, demonstrate high performance in solar cells, and can effectively passivate the perovskite layer’s surface. However, fullerenes have several drawbacks, including expensive and complex synthesis and low solubility in most organic solvents. The availability of suitable alternatives is limited, and most existing alternatives perform worse than fullerenes in solar cells [4].
The aim of this work was to synthesize aromatic phosphine oxide compounds capable of both transporting electrons and passivating the surface of the perovskite crystal. The synthesized compounds were characterized by investigating their thermal stability, ability to sublimate under vacuum, and performance in triple halide 1.68 eV perovskite solar cells of a p-i-n architecture. These compounds were tested both as an interlayer along with fullerene and as a standalone electron-transporting layer.