Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites
Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites
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DOI：
10.1002/adom.201700139
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发表时间：
2017-05
影响因子：
9
通讯作者：
Fengshuo Zu;P. Amsalem;I. Salzmann;Rongbin Wang;Maryline Ralaiarisoa;S. Kowarik;S. Duhm;N. Koch
中科院分区：
文献类型：
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作者：
Fengshuo Zu;P. Amsalem;I. Salzmann;Rongbin Wang;Maryline Ralaiarisoa;S. Kowarik;S. Duhm;N. Koch
本研究利用光电子和吸收光谱研究了白光照射对混合卤化物钙钛矿 (CH3NH3PbI3−xClx) 薄膜和 CH3NH3PbI3 单晶的电子和化学性质的影响。原始材料的表面被发现是 n 型的，因为施主能级的存在导致表面能带弯曲，可能由充当表面陷阱的还原铅 (Pb0) 组成。当用白光（高达 1 个太阳）照射样品时，由于表面光电压，价态特征转变为较低的结合能，即大部分材料的 n 型要少得多。然而，表面光电压仅是部分可逆的，并且随着照明时间的延长而消失。与此同时，发现了高浓度的金属 Pb0，这会引起强烈的费米能级钉扎和表面光电压的猝灭。这还伴随着 PbI2 缺陷的形成。对单晶的类似实验表明，劈裂后样品表面存在高浓度的还原（金属）Pb0。目前的研究结果表明，钙钛矿薄膜的化学和电子特性对白光照射非常敏感。考虑这些光引起的材料变化对于充分了解其光物理特性和提高钙钛矿器件的使用寿命非常重要。
This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and CH3NH3PbI3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb0) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.