The orthorhombic γ-black phase of CsPbI₃ is well-known to be unstable at room temperature and strategies are needed to counteract its transformation tendency. In this paper we compare γ-black CsPbI₃ thin films (∼80 nm) formed via two different routes: a fast quenching of the cubic α-phase from 325 C (HT-γ) or spontaneously cooling the layer from 80 C (LT-γ). The successful application of the second procedure is allowed by the use of a mother solution containing Europium with an Eu/Pb ratio as small as 5%. This has been indeed used to form both LT-γ and HT-γ thin films. The phase transition during the heating and cooling pathways is followed in situ by spectroscopic ellipsometry and x-ray diffraction analyses. We demonstrate that both γ-black phases exhibit the same absorption features and critical points as depicted in very details by the dielectric functions. Minor differences can be found in the intensity of the absorption coefficient, assigned to an improved lattice quality in the layer that has experienced the high temperature path. On the other hand, α-black and δ-yellow phases show different critical points in the optical transitions. Besides providing benchmarking optical parameters to discriminates the different phases, we demonstrate that the LT-γ phase closely competes with the HT-γ counterpart during stress tests for stability, with the first one more suited for tandem monolithic architectures that require thermal treatments under 200 C.

众所周知，CsPbI ₃的斜方晶γ-黑相在室温下不稳定，需要采取策略来抵消其转变趋势。在本文中，我们比较了通过两种不同途径形成的γ-黑 CsPbI ₃薄膜（~80 nm）：从 325 C (HT-γ) 快速淬火立方 α 相或从 80 C (LT -γ）。通过使用含有铕且 Eu/Pb 比率低至 5% 的母液，可以成功应用第二个程序。这确实已用于形成 LT-γ 和 HT-γ 薄膜。原位跟踪加热和冷却路径期间的相变通过光谱椭偏仪和 X 射线衍射分析。我们证明了两种 γ-黑相都表现出相同的吸收特征和临界点，如介电函数所描述的那样。在吸收系数的强度中可以发现细微的差异，这归因于经历了高温路径的层中晶格质量的改善。另一方面，α-黑和δ-黄相在光学跃迁中显示出不同的临界点。除了提供基准光学参数来区分不同的相外，我们还证明了 LT-γ 相在稳定性压力测试期间与 HT-γ 对应物密切竞争，第一个更适合需要在 200 摄氏度以下热处理的串联单片架构.