Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells
Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells
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DOI：
10.1021/jacs.6b06320
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发表时间：
2016-08-17
影响因子：
15
通讯作者：
Hagfeldt, Anders
中科院分区：
文献类型：
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作者：
Jacobsson, T. Jesper;Correa-Baena, Juan-Pablo;Hagfeldt, Anders
在过去的几年里，卤化铅钙钛矿作为光伏应用中的光吸收剂引起了相当大的兴趣，其效率现已达到创纪录的22%。近年来人们发现，精确的化学计量不仅对器件的组成很重要，而且对器件的性能也很重要。例如，最近的报道表明，钙钛矿薄膜中少量的PbI2对标准钙钛矿CH3NH3PbI3以及混合钙钛矿（CH3NH3）(x)-(CH(NH2)(2))((1x))PbBryI（3y）的整体性能都是有益的。在这项工作中，广泛的表征技术，包括x射线衍射（XRD），扫描电子显微镜（SEM），透射电子显微镜（TEM），光电子能谱（PES），瞬态吸收光谱（TAS）， UVvis，电致发光（EL），光致发光（PL）和共聚焦PL映射，已被用于进一步了解钙钛矿太阳能电池中残余PbI2的重要性。我们最好的设备效率超过18%，并且与之前的结果一致，有少量多余的PbI2。对于缺乏pbi2的样品，光电流下降，这可能是由于晶界处有机物质的积累，电荷载流子迁移率低，以及进入TiO2的电子注入减少。然而，缺乏pbi2的组合物也有优势。在pbi2缺失的样品中，记录的V-oc高达1.20 V。这与高晶体质量、更长的载流子寿命和高PL产率相关，并且作为钙钛矿形成动力学的结果被合理化。我们进一步发现，在pbi2缺失的样品中，离子迁移受到阻碍，这降低了JV滞后，提高了光稳定性。因此，缺乏pbi2的合成条件可用于沉积具有优异晶体质量的钙钛矿，但其晶界的缺点是富含有机物质，这对电流的传输起着障碍作用。探索如何调整合成条件，使其在贫pbi2条件下获得高晶体质量，同时保持富pbi2条件下获得的良好晶界特性，将是获得更高效器件的策略。
Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)(x)-(CH(NH2)(2))((1x))PbBryI(3y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UVvis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record V-oc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward current transport. Exploring ways to tune the synthesis conditions to give the high crystal quality obtained under PbI2-poor condition while maintaining the favorable grain boundary characteristics obtained under PbI2-rich conditions would thus be a strategy toward more efficiency devices.