立方α-CsPbI3相因其1.7eV的合适电子带隙而成为太阳能电池应用中最有前途的钙钛矿化合物之一。然而,它在运行条件下表现出结构不稳定性,经常转变为六方非钙钛矿δ-CsPbI3相,由于带隙大,不适合太阳能电池应用(例如,~2.9eV)。因此,人们对确定增加立方α-CsPbI3相稳定性的可能机制越来越感兴趣。这里,我们报告了一项理论调查,基于密度泛函理论计算,α-的表面钝化,γ-,和使用C6H4(NH3)2[对苯二胺(PPD)]和Cs物质作为钝化剂的δ-CsPbI3(100)表面。我们的计算和分析证实了最近的实验发现,表明PPD钝化可以有效地稳定立方α-CsPbI3钙钛矿,使其免受立方到六方的相变。PPD分子与底物表现出共价支配键,这使得它比钙钛矿块中占主导地位的离子键更能抵抗变形。通过将这些结果与天然Cs钝化进行对比,我们强调了PPD钝化的优越稳定性,负表面形成能证明了这一点,与观察到的Cs钝化的正值不同。这种差异是由于PPD的分子/表面相互作用的共价特征,与Cs钝化所看到的纯离子相互作用相反。值得注意的是,PPD钝化保持了钙钛矿的光电性质,因为从PPD分子衍生的电子态位于远离带隙区域,这对光电应用至关重要。
The cubic α-CsPbI3 phase stands out as one of the most promising perovskite compounds for solar cell applications due to its suitable electronic band gap of 1.7 eV. However, it exhibits structural instability under operational conditions, often transforming into the hexagonal non-perovskite δ-CsPbI3 phase, which is unsuitable for solar cell applications because of the large band gap (e.g., ∼2.9 eV). Thus, there is growing interest in identifying possible mechanisms for increasing the stability of the cubic α-CsPbI3 phase. Here, we report a theoretical investigation, based on density functional theory calculations, of the surface passivation of the α-, γ-, and δ-CsPbI3(100) surfaces using the C6H4(NH3)2 [p-phenylenediamine (PPD)] and Cs species as passivation agents. Our calculations and analyses corroborate recent experimental findings, showing that PPD passivation effectively stabilizes the cubic α-CsPbI3 perovskite against the cubic-to-hexagonal phase transition. The PPD molecule exhibits covalent-dominating bonds with the substrate, which makes it more resistant to distortion than the ionic bonds dominant in perovskite bulks. By contrasting these results with the natural Cs passivation, we highlight the superior stability of the PPD passivation, as evidenced by the negative surface formation energies, unlike the positive values observed for the Cs passivation. This disparity is due to the covalent characteristics of the molecule/surface interaction of PPD, as opposed to the purely ionic interaction seen with the Cs passivation. Notably, the PPD passivation maintains the optoelectronic properties of the
perovskites because the electronic states derived from the PPD molecules are localized far from the band gap region, which is crucial for optoelectronic applications.