Organic Cation Alloying on Intralayer A and Interlayer A’ sites in 2D Hybrid Dion–Jacobson Lead Bromide Perovskites (A’)(A)Pb2Br7

Hybrid layered halide perovskites have achieved impressive performance in optoelectronics. New structural types in the two-dimensional (2D) halide system such as the Dion–Jacobson phases have attracted wide research attention due to the short interlayer distance and unique layer orientation that facilitate better charge-transport and higher stability in optoelectronic devices. Here, we report the first solid solution series incorporating both A and A’ cations in the 2D Dion–Jacobson family, with the general formula (A’)­(A)­Pb2Br7 ((A’ = 3-(aminomethyl)­piperidinium (3AMP) and 4-(aminomethyl)­piperidinium) (4AMP); A = methylammonium (MA) and formamidinium (FA)). Mixing the spacing A’ cations and perovskitizer A cations generates the new (3AMP)a(4AMP)1–a(FA)b(MA)1–bPb2Br7 perovskites. The crystallographically refined crystal structures using single-crystal X-ray diffraction data reveal that the distortion of the inorganic framework is heavily influenced by the degree of A’ and A alloying. A rising fraction of 4AMP in the structure, decreases the Pb–Br–Pb angles, making the framework more distorted. On the contrary, higher FA fractions increase the Pb–Br–Pb angles. This structural evolution fine-tunes the optical properties where the larger the Pb–Br–Pb angle, the narrower the band gap. The photoluminescence emission energy mirrors this trend. Raman spectroscopy reveals a highly dynamical lattice similar to MAPbBr3 and consistent with the local distortion environment of the [Pb2Br7] framework. Density functional theory (DFT) calculations of the electronic structures reveal the same trend as the experimental results where (3AMP)­(FA)­Pb2Br7 has the smallest band gap while (4AMP)­(MA)­Pb2Br7 has the largest band gap. The structural effects from solely the organic cations in the 2D system highlight the importance of understanding the high sensitivity of the optoelectronic properties on the structural tuning in this broad class of materials.

杂化层状卤化物钙钛矿（hybrid layered halide perovskites）在光电子学领域已展现出优异性能。二维（two-dimensional，2D）卤化物体系中的新型结构类型——如Dion–Jacobson相（Dion–Jacobson phases）——因层间距较短、层取向独特，可在光电子器件中实现更优异的电荷传输性能与更高稳定性，因此受到了广泛的研究关注。本文首次报道了二维Dion–Jacobson家族中同时包含A与A’阳离子的固溶体系列，其通式为(A’)­(A)­Pb₂Br₇，其中A’为3-(氨甲基)哌啶鎓（3-(aminomethyl)piperidinium，3AMP）与4-(氨甲基)哌啶鎓（4-(aminomethyl)piperidinium，4AMP），A为甲胺鎓（methylammonium，MA）与甲脒鎓（formamidinium，FA）。通过间隔阳离子A’与钙钛矿-forming阳离子（perovskitizer）A的混合，可制备得到新型(3AMP)ₐ(4AMP)₁₋ₐ(FA)ᵦ(MA)₁₋ᵦPb₂Br₇钙钛矿。利用单晶体X射线衍射（single-crystal X-ray diffraction）数据解析得到的晶体精修结构显示，无机骨架的畸变程度受A’与A的合金化程度影响显著。结构中4AMP占比的提升会减小Pb–Br–Pb键角，使骨架畸变程度加剧；与之相反，FA占比的提升则会增大Pb–Br–Pb键角。这种结构演化可对光学性能进行精准调控：Pb–Br–Pb键角越大，带隙（band gap）越窄。光致发光（photoluminescence）发射能量也遵循这一变化趋势。拉曼光谱（Raman spectroscopy）分析显示，该体系具有与MAPbBr₃相似的高动态晶格特性，且与[Pb₂Br₇]骨架的局部畸变环境相符。密度泛函理论（density functional theory，DFT）电子结构计算结果与实验趋势一致：(3AMP)­(FA)­Pb₂Br₇的带隙最小，而(4AMP)­(MA)­Pb₂Br₇的带隙最大。二维体系中仅由有机阳离子带来的结构效应，凸显了理解此类广泛材料体系的光电子性能对结构调控的高敏感性的重要性。