The research group led by Prof. HAN Keli from Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has made a progress in the study of the dynamic mechanism of two-dimensional lead-free perovskite materials. This work has been published in The Journal of Physical Chemistry Letters.

Structural illustration of the layered 2D perovskite (PEA)₂GeI₄ and room-temperature PL spectrum of 2D (PEA)₂GeI₄ and 3D MAGeI₃

Organic-inorganic hybrid perovskites are widely used in the photovoltaic field, in view of their high absorption coefficients, long charge carrier diffusion lengths, and simple manufacturing processes.

However, the heavy metal lead in these materials is toxic to organisms and the environment, and the stability of these material needs to be improved. Accordingly, it is important to develop lead-free and stable perovskite materials.

This group reported a lead-free, two-dimensional perovskite, (PEA)₂GeI₄ (PEA =C₆H₅(CH₂)₂NH₃⁺). Structural characterization demonstrated that this 2D perovskite structure is formed with inorganic germanium iodide planes separated by organic PEAI layers.

(PEA)₂GeI₄ has a direct band gap of 2.12 eV, in agreement with 2.17 eV obtained by density functional theory (DFT) calculations, implying that it is suitable for a tandem solar cell. (PEA)₂GeI₄ luminesces at room-temperature with a moderate lifetime, exhibiting good potential for photovoltaic applications.

In addition, 2D (PEA)₂GeI₄ is more stable than 3D CH₃NH₃GeI₃ in air, owing to the presence of a hydrophobic organic long chain.

This work provides a direction for the development of 2D Ge-based perovskites with potential for photovoltaic applications.

Previously, this group has achieved a series of research results on the mechanism of luminescence dynamics of lead-free perovskite nanocrystals (Angew. Chem. Int. Ed.) and lead-free double perovskite (New J. Chem.). (Text and Image by CHENG Pengfei)