Bandgap-Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells
Bandgap-Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells
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DOI：
10.1002/aenm.201502458
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发表时间：
2016-04-20
影响因子：
27.8
通讯作者：
Snaith, Henry J.
中科院分区：
文献类型：
--
作者：
Sutton, Rebecca J.;Eperon, Giles E.;Snaith, Henry J.
DOI：10.1002/aenm. 201502458的铯铅卤化物[14-21]，这些材料现在引起了光伏和发光社区的兴趣，最近有一些报道称它们被用于太阳能电池和作为发射纳米晶体。[22-27]这些先前的报道使我们对这些无机钙钛矿的组成和结构相稳定性有了更多的了解。我们在这里考虑溴化铯铅（CsPbBr 3）和碘化铯铅（CsPbI 3）：这两种化合物在其熔点超过460 ℃时组成稳定。[16]CsPbBr 3在室温下以正交晶相结晶，在88 ℃转变为四方钙钛矿相，在130 ℃转变为“橙子”立方钙钛矿相. [21，22]相比之下，CsPbI 3在室温下稳定为正交非钙钛矿结构（黄相），当加热至约300 C以上时转变为立方钙钛矿（黑相）。[14不幸的是，CsPbI 3在环境气氛中在黑色钙钛矿相中是不稳定的，并且迅速转化为非钙钛矿黄色相。[14我们注意到，对于尺寸约为5 nm的纳米晶体，这些相变似乎被改变，使得CsPbI 3的纳米晶体在室温下在立方相中比体CsPbI 3更稳定，尽管两者都随着时间恢复到非钙钛矿相。[25]我们预计，在多晶薄膜的相变是类似的散装。因此，对于这些材料，很明显，在陆地太阳能电池工作温度下，结构稳定性是要解决的重要参数，而不是组成稳定性。在CsPbBr 3和CsPbI 3之间的混合卤化物区，在块体材料中形成固溶体。[16]然而，对于薄膜，由于溴离子的溶解度限制，溶液处理对于富含溴化物的组合物是困难的。这个问题最近通过使用两步法来制造纯CsPbBr 3的膜以及随后使用CsPbBr 3作为光吸收材料的太阳能电池而被克服。[22]在这里，我们表明，这种两步方法可以用来形成完整系列的铯铅卤化物钙钛矿薄膜从CsPbBr 3到CsPbI 3。然而，我们发现均匀的薄膜沉积是具有挑战性的。相比之下，我们证明，与一个步骤的解决方案处理路线，我们可以创建具有高碘化物含量的铯钙钛矿的均匀薄膜。基于这些结果，我们选择了适当的混合卤化物组合物，其在环境大气中具有增加的结构稳定性。对于这种材料，我们观察到，当与混合等效物相比时，在85 ℃下在水分存在下具有令人惊讶的上级稳定性。最后，我们用这种带隙为1.92 eV的材料制作了太阳能电池，在室温下在空气中工作，功率转换效率接近10%。在过去的几年里，有机-无机卤化物钙钛矿混合材料已经得到了很好的研究，使用这些材料的太阳能电池在不到五年的时间里效率从3.8%迅速上升到20%以上。[1-4]这些材料通常在卤化铅骨架中包含有机阳离子，例如甲基铵（MA）和/或甲脒鎓（FA）。[5]虽然这些混合钙钛矿太阳能电池表现出高效率，但薄膜钙钛矿吸收层由于热和湿度而受到成分降解，[6]因此，解决长期稳定性是社区的主要关注点。[7]热应力下的组成稳定性对于太阳能电池的运行尤为重要;对于认证太阳能电池组件必须能够在...
DOI: 10.1002/aenm. 201502458 of cesium lead halides,[14–21] and these materials are now garnering interest from both the photovoltaic and light emission communities with a few recent reports of them being used in solar cells and as emissive nanocrystals.[22–27] These previous reports give us much insight into the compositional and structural phase stability of these inorganic perovskites. We consider here cesium lead bromide (CsPbBr 3) and cesium lead iodide (CsPbI 3): both of these compounds are compositionally stable up to their melting points which are in excess of 460 C.[16] CsPbBr 3 crystallizes in an orthorhombic phase at room temperature, and transitions to a tetragonal perovskite phase at 88 C and to the “orange” cubic perovskite phase at 130 C.[21, 22] In contrast, CsPbI 3 is stable in an orthorhombic non-perovskite structure (yellow phase) at room temperature, and changes to the cubic perovskite (black phase) when heated above≈ 300 C.[14, 16] Unfortunately, CsPbI 3 is unstable in the black perovskite phase in ambient atmosphere and rapidly converts to the non-perovskite yellow phase.[14, 23] We note that for nanocrystals on the order of 5 nm in size, these phase transitions appear to be altered such that nanocrystals of CsPbI 3 are more stable in the cubic phase at room temperature than bulk CsPbI 3, although both revert to the non-perovskite phase over time.[25] We expect the phase transitions in the polycrystalline films to be similar to those in the bulk. Hence, for these materials, it is apparent that the structural stability is the important parameter to resolve, rather than the compositional stability, under terrestrial solar cell operating temperatures. In the mixed halide region between CsPbBr 3 and CsPbI 3, solid solutions form in the bulk material.[16] However, for thin films, solution processing is difficult for the bromide-rich compositions, due to solubility limitations of the bromide ion. This problem was recently overcome by using a two-step method to make films of neat CsPbBr 3, and subsequent solar cells using CsPbBr 3 as the light absorbing material.[22] Herein, we show that this two-step method can be used to form the full series of cesium lead halide perovskite thin films from CsPbBr 3 to CsPbI 3. However, we find that uniform film deposition is challenging. In contrast, we demonstrate that with a one-step solution processing route we can create uniform thin films of cesium perovskites with high iodide content. Based on these results we select an appropriate mixed halide composition with increased structural stability in ambient atmosphere. For this material we observe surprisingly superior stability at 85 C in the presence of moisture when compared with a hybrid equivalent. Finally, we fabricate solar cells with this 1.92 eV band gap material which operate in air at room temperature with close to 10% power conversion efficiency (PCE).Hybrid organic–inorganic halide perovskite materials have been well-studied in the past few years, and solar cells using these materials have seen a rapid rise in efficiency from 3.8% to over 20% in less than five years.[1–4] These materials typically comprise organic cations, such as methylammonium (MA) and/or formamidinium (FA), in a lead halide framework.[5] Although these hybrid perovskite solar cells exhibit high efficiencies, the thin-film perovskite absorber layers are subject to compositional degradation due to both heat and humidity,[6] therefore, addressing the long-term stability is a primary concern for the community.[7] Compositional stability under thermal stressing is particularly important for solar cell operation; for certification solar modules must be able to operate successfully between …