Mixed halide perovskites (MHPs) have attracted attention due to their tunability of optoelectronic properties and especially the bandgap, which is useful for tandem solar cells. Unfortunately, MHPs undergo phase separation under illumination. It can form low-bandgap iodide-rich phases as charge recombination centers, causing the reduction of open-circuit voltage (Voc) and device photoinstability. To address this issue, many approaches have been used[1]. In ABX3 MHPs, A-site can be CH3NH3 (MA+), CH(NH2)2 (FA+) or Cs+, B-site can be Pb2+ or Sn2+, and X-site is dominated by halide anion (Cl–, Br– or I–). The composition engineering on A/B/X sites can effectively alleviate the photoinduced phase separation. Photoinduced phase separation is common in MHPs with single cation at A-site, in which typical red shift in photoluminescence (PL) upon light illumination can be observed[2]. A-site doping is an effective way to retard phase segregation. The introduction of Cs+ into A-site could inhibit photoinduced phase segregation[3]. A time-dependent red-shift in PL was observed for MAPb(I0.6Br0.4)3 film (Fig. 1(a)). But no significant red-shift in PL was observed in FA0.83Cs0.17Pb(I0.6Br0.4)3 film after identical light illumination. Dang et al. observed the positive effect of Cs+ and Rb+ doping on phase segregation[4]. A-site doping mechanism was explained by the polarization model[5]. Electron–phonon coupling can induce lattice distortion, thus causing phase separation. Phenomenological model showed that lowering electron–phonon coupling can reduce the tendency of photoinduced phase separation[5]. A strong correlation exists between Cs+ doping and photoinduced halide segregation. Excessive Cs+ doping could also cause photoinduced phase segregation (Fig. 1(b))[6]. Adjusting B-site composition can improve phase stability under illumination. The photoinduced phase segregation was widely reported as the intrinsic instability of CsPbIBr2. Li et al. inhibited photoinduced phase segregation and improved device stability by partially replacing Pb2+ with Sn2+[7]. The PL peak of CsPbIBr2 split into two peaks after illumination, corresponding to iodideand bromide-rich phases (Fig. 1(c)). No obvious photoinduced phase segregation was seen in CsPb0.75Sn0.25IBr2 film[7]. The stabilization of I/Br phase in MAPb0.75Sn0.25(I1–yBry)3 was also reported by Yang et al.[8], who further speculated that internal bonding environment was changed by partial Sn substitution to suppress halogen phase separation. I–/Br–-mixed MHPs present increased chemical stability and suitable bandgap for tandem cells. Xu et al. announced efficient perovskite top cells (1.67 eV) by using triple-halide alloys (Cl–/I–/Br–) to tailor the bandgap and stabilize perovskite under illumination[9]. From double-halide to triple-halide alloy, an enhancement in optoelectronic properties was observed, e.g., remarkable improvements in photocarrier lifetime and mobility, significant suppression of photoinduced phase segregation under illumination up to 100 suns (Fig. 1(d)). The corresponding solar cells maintained >96% of their initial efficiency after 1000 h operation under white light illumination at 60 °C. Photoinduced phase segregation likes to take place at grain boundaries. Hu et al. studied the role of grain boundary's area and grain orientation in phase separation of MHPs[10]. The enhanced crystallinity and grain size of CH3NH3PbIxBr3–x films could stabilize these materials under one sun illumination, which enhanced the device efficiency and stability (Fig. 2(a))[10]. The grain boundary defects, particularly halide vacancies in perovskite lattice, contribute expansive channels for photo-driven migration of halide ions. Interface passivation proves to be another effective approach to suppress photoinduced phase separation. Abdi-Jalebi et al. reported that the surface and grain boundary defects could be passivated by potassium[11]. The external photoluminescence quantum efficiency (PLQE) as a function of time for (Cs,FA,MA)Pb(I0.85Br0.15)3 films were measured at excitation densities equivalent to that of solar illumination (Fig. 2(b)), and the photoinduced migration was inhibited by increasing potassium content. Zhou et al. constituted a CsPbBr3-cluster passivated perovskite structure with high-quality CsFAMA films, where CsPbBr3-clusters were located at the surface/interface of CsFAMA grains (Fig. 2(c))[12]. Belisle et al. indicated that surface modification was also an effective approach to suppress the photoinduced phase separation in MHPs[13]. Coating a perovskite surface with electron-donating ligand trioctylphosphine oxide (TOPO) could not only reduce nonradiative recombination but also retard halide segregation in CH3NH3PbI2Br films. A kinetic model raised by Draguta et al. revealed that photoinduced phase separation in MHPs could be suppressed by reducing carrier diffusion lengths (le/h) because the rate of

中文翻译：

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抑制混合卤化物钙钛矿中的光致相偏析

混合卤化物钙钛矿（MHPs）由于其光电特性的可调谐性，尤其是可用于串联太阳能电池的带隙而引起了人们的关注。不幸的是，MHP 在光照下会发生相分离。它可以形成低带隙富含碘化物的相作为电荷复合中心，导致开路电压（Voc）降低和器件光不稳定性。为了解决这个问题，已经使用了许多方法[1]。在 ABX3 MHPs 中，A 位可以是 CH3NH3 (MA+)、CH(NH2)2 (FA+) 或 Cs+，B 位可以是 Pb2+ 或 Sn2+，X 位主要是卤化物阴离子（Cl-、Br- 或我-）。A/B/X位点的组成工程可以有效缓解光致相分离。光致相分离在 A 位单阳离子的 MHP 中很常见，其中可以观察到光照下光致发光 (PL) 的典型红移[2]。A位掺杂是一种有效的延缓相偏析的方法。将 Cs+ 引入 A 位可以抑制光致相偏析[3]。对于 MAPb(I0.6Br0.4)3 薄膜，观察到 PL 的时间依赖性红移（图 1(a)）。但在相同光照条件下，FA0.83Cs0.17Pb(I0.6Br0.4)3薄膜的PL没有明显红移。党等人。观察到 Cs+ 和 Rb+ 掺杂对相分离的积极影响[4]。极化模型[5]解释了A位掺杂机制。电子-声子耦合会引起晶格畸变，从而导致相分离。唯象模型表明，降低电子-声子耦合可以降低光致相分离的趋势[5]。Cs+ 掺杂和光致卤化物偏析之间存在很强的相关性。过多的 Cs+ 掺杂也会导致光致相偏析（图 1（b））[6]。调整 B 位组成可以提高光照下的相位稳定性。光致相分离被广泛报道为 CsPbIBr2 的固有不稳定性。李等人。通过用 Sn2+ 部分替代 Pb2+，抑制光致相分离并提高器件稳定性 [7]。CsPbIBr2 的 PL 峰在光照后分裂成两个峰，对应于富含碘化物和溴化物的相（图 1（c））。CsPb0.75Sn0.25IBr2薄膜中未见明显的光致相偏析[7]。Yang 等人也报道了 MAPb0.75Sn0.25(I1-yBry)3 中 I/Br 相的稳定性[8]，谁进一步推测内部键合环境通过部分Sn取代来改变以抑制卤素相分离。I-/Br-混合的 MHP 具有更高的化学稳定性和适合串联电池的带隙。徐等人。宣布通过使用三卤化物合金（Cl-/I-/Br-）来调整带隙并在光照下稳定钙钛矿[9]，从而获得高效的钙钛矿顶部电池（1.67 eV）。从双卤化物到三卤化物合金，观察到光电性能的增强，例如光载流子寿命和迁移率的显着改善，在高达 100 个太阳光照下的光致相偏析显着抑制（图 1（d））。相应的太阳能电池在 60°C 的白光照射下运行 1000 小时后保持 >96% 的初始效率。光致相偏析喜欢发生在晶界处。胡等人。研究了晶界面积和晶粒取向在 MHPs 相分离中的作用[10]。CH3NH3PbIxBr3-x 薄膜提高的结晶度和晶粒尺寸可以在一次阳光照射下稳定这些材料，从而提高器件的效率和稳定性（图 2（a））[10]。晶界缺陷，特别是钙钛矿晶格中的卤化物空位，为卤化物离子的光驱动迁移提供了广阔的通道。界面钝化被证明是抑制光致相分离的另一种有效方法。Abdi-Jalebi 等人。报道了表面和晶界缺陷可以被钾钝化[11]。(Cs,FA,MA)Pb(I0.85Br0.) 的外部光致发光量子效率 (PLQE) 作为时间的函数。15) 3 薄膜在与太阳光照相当的激发密度下测量（图 2（b）），并且通过增加钾含量来抑制光诱导迁移。周等人。形成了具有高质量 CsFAMA 薄膜的 CsPbBr3 簇钝化钙钛矿结构，其中 CsPbBr3 簇位于 CsFAMA 晶粒的表面/界面处（图 2（c））[12]。贝利斯尔等人。表明表面改性也是抑制 MHPs 中光致相分离的有效方法[13]。用给电子配体三辛基氧化膦 (TOPO) 涂覆钙钛矿表面不仅可以减少非辐射复合，还可以延缓 CH3NH3PbI2Br 薄膜中的卤化物偏析。Draguta 等人提出的动力学模型。