高性能的准二维钙钛矿发光二极管(quasi-2D PeLEDs)是钙钛矿光电器件领域中的一个热点研究课题。由于准二维钙钛矿晶体由八面体和大有机阳离子交替平面组成，其相分布（n）决定了八面体层内的量子约束效应以及与有机间隔阳离子的相互作用。通常情况下n由前驱体溶液的化学计量控制，但在后续的薄膜加工过程中，受晶体生长动力学和热力学因素的影响，会形成从n=1到n=∞的宽相分布。低维相的大量聚集，不连续的相分布以及高缺陷浓度都极大限制了器件的效率。为了实现准二维钙钛矿薄膜的高质量发光，必须调整相的均匀分布并减少缺陷。然而，钙钛矿n值的调控一直是该领域的难点，且在不同的化学组分中，n调控具有极大的差异性，这意味着钙钛矿薄膜的相分布调控面临困难，且调控策略的普适性也是一个难题。因此，本团队提出使用苄基磷酸添加剂来研究钙钛矿的相分布调节过程，从薄膜相分布变化趋势和高效的器件发光视角为调节quasi-2D 钙钛矿的相分布和钝化缺陷提供了可行的策略，且在多个化学组分配方的蓝绿发光波段得到了普适性验证。

本工作提出引入苄基磷酸（BPA）来调控钙钛矿相分布不均匀问题。研究过程中我们以PEA₂Cs_n−1Pb_nBr_3n+1绿光和[(PEA)_0.75(GA)_0.25]₂CsPb₂X₇蓝光为研究对象，通过在钙钛矿前驱体溶液中掺杂不同化学浓度的BPA添加剂，调控准二维薄膜的相分布和减少薄膜缺陷态密度。研究表明，含有多个P=O和P-OH位点的BPA分子在钙钛矿膜形成过程中可以吸引和锚定PEA⁺/Pb²⁺，使其充分成核生长。这种相互作用抑制了低维相(n=1)的形成，促进了以n≥2相为主的中间相连续生长，使得能量由低n相向高n相的转移更加通畅。这种有效的相分布调控不仅优化了绿光钙钛矿器件性能(e.g., luminance @ 24,352 cd/m²，EQE @ 20.6 %)，同时在蓝光钙钛矿器件中也有很好的表现(e.g., luminance @ 5264 cd/m²，EQE @ 8 %)，这说明了BPA对PEA⁺/Pb²⁺的锚定效应及其相位分布规律具有普适性，为实现高性能quasi-2D PeLEDs提供了一种可行的策略。

Figure 1 The effect of BPA on the phase distribution of perovskite films. (a) A schematic diagram of the energy transfer process of typical perovskite films and (b) the crystallization process of perovskite after adding BPA. (c) The normalize UV-vis absorption spectra of quasi-2D perovskite films with and without addition of BPA. (d-e) Infrared spectra of quasi-2D perovskite films with and without addition of BPA. (f) ¹H NMR spectra of BPA, BPA+PbBr₂, and BPA+PEABr dissolved in DMSO-d₆.

Figure 2 Research on PL of perovskite films. (a) Steady state PL spectra and (b) TRPL curves of perovskite films treated with different concentrations of BPA. (c) Schematic diagram of PL Mapping treated with pristine film and different concentrations of BPA, including pristine, BPA 2.5 mg/ml, BPA 5 mg/ml, and BPA 10 mg/ml from top to bottom. (d) Statistical diagram of the corresponding spatial steady-state fluorescence lifetime distribution.

Figure 3 Characterization of surface morphology of perovskite films. (a) AFM schematic diagram of the pristine film and (b) BPA 2.5 mg/ml, (c) BPA 5 mg/ml, and (d) BPA 10 mg/ml treated films. (e) The normalize XRD spectra of perovskite films.

Figure 4 Study on the electrical properties of perovskite films. (a) Hole-only perovskite device structure and (b) J-V curve. (c) Schematic diagram of perovskite film LED and (d) low-frequency 1/ noise treated with pristine films and different concentrations of BPA. (e) Schematic diagram of device capacitance-frequency curve changes and (f) corresponding carrier dynamics processes at different stages.

Figure 5 Study on EL of perovskite films. (a) Device energy level diagram. (b) Current density-voltage (J-V) curves of PeLED devices. (c) The normalize EL spectra of PeLED devices treated with pristine and BPA (5 mg/ml) at the voltage of 6.8 V. (d) Voltage-EQE and (e) Current density-luminance (J-L) curves of PeLED devices. (f) T50 of PeLEDs with an initial luminance of 100 cd/m². 

Tang J, Wang Y, Xiang H, et al. Multi-site anchoring lead-halide octahedral by benzylphosphonic acid to regulate phase distribution for efficient PeLEDs. Nano Research, 2024, https://doi.org/10.1007/s12274-024-6914-9.