The long-term stability on perovskite surfaces limits the practical application of perovskite solar cells (PSCs). Adding multifunction ligand can deal with this issue, however, the structure diversity of ligand and perovskite surface leads to the complicated adsorptive interaction, affecting the improvement effect of the stability and photoelectric properties. In this work, strongly electronegative fluorine atoms and alkyl chain with different length are introduced into aromatic ligand dipole to modify the polarity, regulating the phase stability, energy state and photoelectric properties of formamidinium perovskite (FAPbI) surfaces. The results show the adsorption and interaction energy of positive ligand dipoles on the I-terminated surface decrease with the increase of polarity, which displays stronger ordered π-π stack and adsorption anchoring of ligand dipoles and thus decreasing the formation energy to improve the phase stability. The positive 4-Trifluoromethyl-phenethylammonium (CF3-PEA) with the highest polarity obtains the highest stability and shifts work function (WF) upward from 6.21 eV to the highest 6.46 eV. The negative CF3-PEA adsorbs on the PbI-terminated surface induced by CF3•••Pb and π•••I interaction, achieving the stable phase with lower formation energy and lowest WF 5.61 eV. This work provides tutorial for optimizing performance of PSCs by the addition of ligand dipoles.

中文翻译：

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在芳香配体偶极子上添加氟原子和烷基链以增强甲脒钙钛矿表面的稳定性和光电性能

钙钛矿表面的长期稳定性限制了钙钛矿太阳能电池（PSC）的实际应用。添加多功能配体可以解决这个问题，但配体和钙钛矿表面的结构多样性导致复杂的吸附相互作用，影响稳定性和光电性能的改善效果。该工作将强电负性的氟原子和不同长度的烷基链引入芳香配体偶极子中，以改变极性，调节甲脒钙钛矿（FAPbI）表面的相稳定性、能态和光电性能。结果表明，I端表面正配体偶极子的吸附和相互作用能随着极性的增加而降低，表现出更强的有序π-π堆积和配体偶极子的吸附锚定，从而降低形成能，提高相稳定性。极性最高的正4-三氟甲基苯乙基铵（CF3-PEA）获得最高的稳定性，并将功函数（WF）从6.21 eV向上移动到最高的6.46 eV。通过CF3•••Pb 和π•••I 相互作用诱导负性CF3-PEA 吸附在PbI 封端表面上，实现具有较低形成能和最低WF 5.61 eV 的稳定相。这项工作提供了通过添加配体偶极子来优化 PSC 性能的教程。