Lee Michael, Vigil Julian A, Jiang Zhiqiao, Karunadasa Hemamala I
Department of Chemistry, Stanford University Stanford California 94305 USA
Department of Chemical Engineering, Stanford University Stanford California 94305 USA.
Chem Sci. 2025 Apr 28. doi: 10.1039/d4sc08092k.
Sunlight-induced halide segregation in (CHNH)Pb(Br I ) (1 > > 0.2), which limits obtainable voltages from solar cells with these perovskite absorbers, reverses upon resting in the dark. However, sustained illumination at 1 sun opens a new decomposition pathway, leading to irreversible I loss in an open system. We conclusively show I off-gassing from halide-segregated (CHNH)Pb(BrI) by trapping gaseous I and tracking the electronic conductivity of the perovskite, which increases from electron-doping as iodides are oxidized to iodine. Importantly, we show that this reaction occurs across the perovskite-air solid-gas interface, without confounding effects from solvent or reactive solid interfaces. This characterization was conducted under a nitrogen atmosphere, avoiding vacuum- and oxygen-driven I loss pathways. Consistent observations of I loss upon light-soaking CsPb(BrI) films show that this reaction is intrinsic to the inorganic framework. We propose that the disruption of iodide-rich domains in the halide-segregated films through I loss can masquerade as a light-induced healing or apparent remixing of the segregated film, when in fact it leads to irreversible decomposition. Although I off-gassing is less likely in bromide-rich solid solutions, light-induced halide segregation brings the iodides into proximity and forms electronic states that are energetically poised to trap and accumulate holes, providing a driving force for I loss. Thus, even bromide-rich mixed-halide perovskite absorbers will benefit from I-impermeable encapsulation for long-term stability.
在(CHNH)Pb(BrₓI₁₋ₓ)（1＞x＞0.2）中，阳光诱导的卤化物偏析会限制使用这些钙钛矿吸收剂的太阳能电池所能获得的电压，而在黑暗中静置时这种偏析会逆转。然而，在1个太阳光照强度下持续照射会开启一条新的分解途径，导致在开放系统中碘发生不可逆损失。我们通过捕获气态碘并跟踪钙钛矿的电导率，确凿地证明了卤化物偏析的(CHNH)Pb(BrₓI₁₋ₓ)中碘的脱气现象，随着碘化物被氧化为碘，电导率因电子掺杂而增加。重要的是，我们表明该反应发生在钙钛矿-空气固-气界面，不存在溶剂或反应性固体界面的混杂影响。这种表征是在氮气气氛下进行的，避免了真空和氧气驱动的碘损失途径。对CsPb(BrₓI₁₋ₓ)薄膜进行光浸泡后碘损失的一致观察表明，该反应是无机框架所固有的。我们提出，通过碘损失破坏卤化物偏析薄膜中富含碘的区域，可能会伪装成偏析薄膜的光诱导愈合或明显的重新混合，而实际上这会导致不可逆的分解。尽管在富含溴化物的固溶体中碘脱气的可能性较小，但光诱导的卤化物偏析会使碘化物靠近并形成能量上易于捕获和积累空穴的电子态，从而为碘损失提供驱动力。因此，即使是富含溴化物的混合卤化物钙钛矿吸收剂，也将受益于不透碘的封装以实现长期稳定性。
