The exploration of 2D perovskites and chiral nonlinear optical materials has drawn significant interest due to their structural tunability and strong optical responses. However, the development of quasi-2D perovskites has long been constrained by the limited choice of A-site cations imposed by the traditional tolerance factor. In this study, we present a new 2D tri-layered lead bromide perovskite (4AM)4Pb3Br10 (n = 3) with the general formula (A')2(A)n -1MnX3 n +1, in which 4-aminomonpholine cations (4AM) that act simultaneously as A-site and spacer components, exhibiting an ultrahigh tolerance factor of 1.74-far beyond conventional limits. Crystallizing in the polar space group Cc, the compound shows an order-disorder ferroelectric phase transition at 418 K. Interestingly it also exhibits notable chiral nonlinear optical properties, including strong second-harmonic generation circular dichroism (gSHG-CD ≈ 0.63). This work breaks the classic tolerance factor constraint and opens a pathway for designing new chiral nonlinear optical materials in low-dimensional perovskites.
Fan et al. (Sun,) studied this question.