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Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites

机译：限制性能的纳米级陷阱簇在卤化物钙钛矿中的晶界处。

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摘要

Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices(1,2). This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively(3)) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects(4). Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance(5), perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance(6). The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions(7) and with local strain(8), both of which make devices less stable(9). Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process(10,11), we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices.
机译：卤化物钙钛矿材料在低成本光电应用中具有良好的性能特征。由钙钛矿吸收体制成的光伏器件在单结器件中达到了25％以上的功率转换效率，在串联器件中达到了28％的功率转换效率（1,2）。这种强大的性能（尽管分别低于实际极限值分别约30％和35％（3））在低温下由溶液加工而成的薄膜中令人惊讶，这种方法通常会产生大量的晶体缺陷（4）。尽管点缺陷通常只在钙钛矿带隙中感应出较浅的电子态，而不会影响性能（5），但钙钛矿器件在带隙内仍具有许多能俘获电荷载流子并使它们非辐射复合的状态。这些深陷阱状态因此引起光致发光的局部变化并限制了器件性能（6）。这些陷阱态的起源和分布是未知的，但它们与混合卤化物钙钛矿成分中的光诱导卤化物偏析（7）和局部应变（8）有关，这两者都使器件不稳定（9）。在这里，我们使用光发射电子显微镜对最新的卤化物钙钛矿薄膜中的陷阱分布进行成像。而不是在光致发光效率差的区域内相对均匀的分布，我们观察到离散的纳米级陷阱簇。通过将显微镜测量结果与扫描电子分析技术相关联，我们发现这些陷阱簇出现在晶体学和组成上不同的实体之间的界面上。最后，通过产生时间分辨的光激发载流子俘获过程的光发射序列（10,11），我们揭示了一个空穴俘获特征，其动力学受空穴向局部俘获簇扩散的限制。我们的方法表明，在纳米尺度上管理结构和组成对于卤化物钙钛矿器件的最佳性能至关重要。

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    《Nature》 |2020年第7803期|360-366|共7页
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    Univ Cambridge Cavendish Lab Cambridge England;

    Okinawa Inst Sci & Technol Grad Univ Femtosecond Spect Unit Onna Son Japan;

    Univ Cambridge Dept Mat Sci & Met Cambridge England;

    Univ Cambridge Cavendish Lab Cambridge England|UCL Inst Mat Discovery London England;

    Imperial Coll London Dept Mat London England|Kyungpook Natl Univ Dept Phys Daegu South Korea;

    Yonsei Univ Dept Mat Sci & Engn Seoul South Korea;

    Imperial Coll London Dept Mat London England|Yonsei Univ Dept Mat Sci & Engn Seoul South Korea;

    Univ Cambridge Cavendish Lab Cambridge England|Univ Cambridge Dept Chem Engn & Biotechnol Cambridge England;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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