Two-dimensional (2D) perovskites have emerged as promising optoelectronic materials due to their excellent environmental stability. Tuning the dipole moment of organic spacers has the potential to lower the exciton binding energy (Eb) of 2D perovskites and improve their photovoltaic performance.
Liu Yongsheng and others from Nankai University developed two azetidine secondary ammonium spacers with different electron-withdrawing groups, namely 3-hydroxyazetidine (3-OHAz) and 3,3-difluoroazetidine. Butane (3,3-DFAz) spacer for 2D Ruddlesden-Popper (RP) perovskites.
The study found that the large dipole moment of the fluorinated dipole spacer can effectively enhance the interaction between the organic spacer and the inorganic layer, thereby improving the charge dissociation in the two-dimensional RP perovskite. 2D perovskites using 3,3-DFAz as spacers also exhibit improved film quality, optimized energy level alignment, and reduced exciton binding energy compared to 3-OHAz spacers.
Therefore, the efficiency of 2D perovskite (n = 4 ) devices based on 3,3-DFAz is as high as 19.28%, exceeding that of 3-OHAz-Pb devices (PCE = 11.35%). When mixed A-site cations of MA0.95FA0.5 are used, the efficiency is further increased to 19.85%. This work provides an effective strategy to adjust the energy level alignment and reduce Eb by adjusting the dipole moment of the organic spacer, ultimately achieving the development of high-performance two-dimensional perovskite solar cells .
Hao Zhang, Rui Wang, Liu Yang, Ziyang Hu, Hang Liu, Yongsheng Liu, Angew. Chem. Int. Ed. 2024, e202318206.
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