Metal halide perovskite materials have been widely studied recently due to their excellent optoelectronic properties. Among these materials, organic-inorganic hybrid perovskites have attracted much attention because of their relatively soft framework, which makes them more suitable for nonlinear optical (NLO) applications. However, there is rare physical mechanism study on the coexistence of two-photon absorption (TPA) and saturable absorption (SA) in organic-inorganic hybrid perovskite materials. To clarify this issue, the NLO properties of mixed cation perovskite MA1−xFAxPbI3 [MA=CH3NH3,FA=CH(NH2)2, x=0, 0.2, 0.4, 0.6, and 0.8] thin films are investigated in this paper. Based on the nonlinear transmittance and femtosecond-transient absorption spectrum measurements, it is found that the MA1−xFAxPbI3 materials exhibit NLO behavior dependent on excitation intensity. The TPA coefficient of MA1−xFAxPbI3 decreases with the increase of formamidinium (FA) content, while the relevant saturable intensity increases. In addition, it is revealed that the linear absorption process from valence band 2 to valance band 1 still exists even under a very low excitation intensity. With the increase of excitation intensity, the light transmittance at 1300 nm decreases first and then increases sharply, which also supports the explanation for the coexistence of TPA and SA. It is expected that our findings will promote the application of perovskite materials in nonlinear optoelectronic devices.

中文翻译：

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混合有机阳离子对三碘化铅钙钛矿非线性光学性能的影响

由于其优异的光电性能，金属卤化物钙钛矿材料最近得到了广泛的研究。在这些材料中，有机-无机杂化钙钛矿因其相对柔软的骨架而备受关注，这使得它们更适合非线性光学（NLO）应用。然而，关于有机-无机杂化钙钛矿材料中双光子吸收（TPA）和饱和吸收（SA）共存的物理机制研究很少见。为了澄清这个问题，本文研究了混合阳离子钙钛矿 MA1−xFAxPbI3 [MA=CH3NH3,FA=CH(NH2)2, x=0、0.2、0.4、0.6 和 0.8] 薄膜的 NLO 特性。基于非线性透射率和飞秒瞬态吸收光谱测量，发现 MA1-xFAxPbI3 材料表现出依赖于激发强度的 NLO 行为。MA1−xFAxPbI3 的 TPA 系数随着甲脒（FA）含量的增加而降低，而相关的饱和强度增加。此外，表明即使在非常低的激发强度下，从价带2到价带1的线性吸收过程仍然存在。随着激发强度的增加，1300 nm处的透光率先降低后急剧增加，这也支持了TPA和SA共存的解释。预计我们的发现将促进钙钛矿材料在非线性光电器件中的应用。而相关的饱和强度增加。此外，揭示了即使在非常低的激发强度下，从价带2到价带1的线性吸收过程仍然存在。随着激发强度的增加，1300 nm处的透光率先降低后急剧增加，这也支持了TPA和SA共存的解释。预计我们的发现将促进钙钛矿材料在非线性光电器件中的应用。而相关的饱和强度增加。此外，揭示了即使在非常低的激发强度下，从价带2到价带1的线性吸收过程仍然存在。随着激发强度的增加，1300 nm处的透光率先降低后急剧增加，这也支持了TPA和SA共存的解释。预计我们的发现将促进钙钛矿材料在非线性光电器件中的应用。这也支持了对 TPA 和 SA 共存的解释。预计我们的发现将促进钙钛矿材料在非线性光电器件中的应用。这也支持了对 TPA 和 SA 共存的解释。预计我们的发现将促进钙钛矿材料在非线性光电器件中的应用。