Reversible Hydration of CH3NH3Pbl3 in Films, Single Crystals, and Solar Cells
Reversible Hydration of CH3NH3Pbl3 in Films, Single Crystals, and Solar Cells
复制标题
DOI：
10.1021/acs.chemmater.5b00660
复制
发表时间：
2015-05-12
影响因子：
8.6
通讯作者：
Barnes, Piers R. F.
中科院分区：
文献类型：
--
作者：
Leguy, Aurelien M. A.;Hu, Yinghong;Barnes, Piers R. F.
由甲基铵碘铅钙钛矿(MAPI)组成的太阳能电池因其对水分的敏感性而臭名昭著。我们表明：(1)当MAPI在室温下暴露于水蒸气中时，会形成水合晶相；(Ii)当材料随后干燥时，这些相变完全相反。用时间分辨X射线衍射仪和椭圆偏振法观察到了在长曝光时间下，CH3NH3PbI3中心点H2O和(CH3NH3)(4)PbI6中心点2H(2)O的可逆形成过程。与水蒸气不同，液态水的存在导致MAPI不可逆地分解形成PbI2。在水化过程中，MAPI由深棕色变为透明；测定了CH3NH3PbI3中心点H2O的精确光学常数，禁带宽度为3.1 eV。利用单晶光学常数和薄膜椭偏测量，模拟了MAPI薄膜在潮湿条件下随时间的变化。结果表明，单水相的形成与膜的深度无关，表明水分子沿晶界的快速传输。未封装太阳能电池的气相水合(初始J(Sc)约为19 mA cm(-2)，V-oc约为1.05V)导致短路光电流下降90%以上，开路电位损失接近200 mV；然而，这些损失在干燥的氮气中暴露6h后完全逆转。脱水后电流-电压特性的滞后显著增加，这可能与水合物重结晶后MAPI的缺陷密度和形貌的变化有关。根据我们的观察，我们认为MAPI在水蒸气存在下的不可逆分解只有在颗粒完全转化为一水相时才会发生。
Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (1) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3 center dot H2O followed by (CH3NH3)(4)PbI6 center dot 2H(2)O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using "solvent engineering", single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3 center dot H2O formed on single crystal's were determined, with bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water molecules along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially J(sc) approximate to 19 mA cm(-2) and V-oc approximate to 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and similar to 200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current-voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations, we suggest that irreversible decomposition of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase.