物理化学学报 >> 2021, Vol. 37 >> Issue (4): 2007084.doi: 10.3866/PKU.WHXB202007084

所属专题： 金属卤化物钙钛矿光电材料和器件

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SCN掺杂提高CsPbI3胶体量子点的稳定性和光探测性能

郑超, 刘阿强, 毕成浩, 田建军()   

  • 收稿日期:2020-07-28 录用日期:2020-08-27 发布日期:2020-09-01
  • 通讯作者: 田建军 E-mail:tianjianjun@mater.ustb.edu.cn
  • 基金资助:
    国家自然科学基金(51961135107);国家自然科学基金(51774034);北京自然科学基金(2182039);国家重点研发计划(2017YFE0119700)

SCN-doped CsPbI3 for Improving Stability and Photodetection Performance of Colloidal Quantum Dots

Chao Zheng, Aqiang Liu, Chenghao Bi, Jianjun Tian()   

  • Received:2020-07-28 Accepted:2020-08-27 Published:2020-09-01
  • Contact: Jianjun Tian E-mail:tianjianjun@mater.ustb.edu.cn
  • About author:Jianjun Tian, Email: tianjianjun@mater.ustb.edu.cn. Tel.: +86-10-8237-7502
  • Supported by:
    the National Natural Science Foundation of China(51961135107);the National Natural Science Foundation of China(51774034);the Beijing Natural Science Foundation(2182039);the National Key Research and Development Program of China(2017YFE0119700)

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摘要：

无机卤化物钙钛矿CsPbI3胶体量子点因其优越的光电性能在光伏和发光器件领域中表现出极大的发展前景。然而，CsPbI3较差的稳定性阻碍了实际应用。为此，我们采用SCN−离子掺杂CsPbI3 (SCN-CsPbI3)量子点用于提高量子点的光学性能和稳定性。研究表明，SCN−离子掺杂不仅减少了量子点缺陷、改善了光学性能，还提高了Pb－X键能、量子点结晶质量以及钙钛矿结构稳定性。结果表明，SCN-CsPbI3量子点的荧光量子产率(PLQY)超过90%，远高于未掺杂原始样品(PLQY为68%)。高的荧光量子产率表明量子点具有较低的缺陷态密度，这归咎于缺陷的减少。空间限制电荷和时间分辨荧光光谱等研究也证实SCN−离子掺杂减少了量子点的缺陷。此外，SCN-CsPbI3量子点展现出很好的抗水性能，其荧光强度在水中浸泡4 h后依然保持85%的初始值。而未掺杂原始样品的荧光性能很快消失，这是因为水诱导其相变。基于SCN-CsPbI3量子点的光电探测器表现出宽波域响应(400–700 nm)，高的响应率(90 mA∙W−1)和超过1011 Jones的探测度，远高于未掺杂原始量子点探测器的性能(响应率为60 mA∙W−1和探测度为1010 Jones)。

关键词: 无机卤化物钙钛矿, 量子点, 掺杂, 稳定性, 光电探测器

Abstract:

Inorganic halide CsPbI3 perovskite colloidal quantum dots (QDs) possess remarkable potential in photovoltaics and light-emitting devices owing to their excellent optoelectronic performance. However, the poor stability of CsPbI3 limits its practical applications. The ionic radius of SCN− (217 pm) is comparable to that of I− (220 pm), whereas it is marginally larger than that of Br− (196 pm), which increases the Goldschmidt tolerance factor of CsPbI3 and improves its structural stability. Recent studies have shown that adding SCN− in the precursor solution can enhance the crystallinity and moisture resistance of perovskite film solar cells; however, the photoelectric properties of the material post SCN− doping remain unconfirmed. To date, it has not been clarified whether SCN− doping occurs solely on the perovskite surfaces, or if it advances within their structures. In this study, we synthesized inorganic perovskite CsPbI3 QDs via a hot-injection method. Pb(SCN)2 was added to the precursor for obtaining SCN−-doped CsPbI3 (SCN-CsPbI3). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were conducted to demonstrate the doping of SCN− ions within the perovskite structures. XRD and TEM indicated a lattice expansion within the perovskite, stemming from the large steric hindrance of the SCN− ions, along with an enhancement in the lattice stability due to the strong bonding forces between SCN− and Pb2+. Through XPS, we confirmed the existence of the S peak, and further affirmed that the bonding energy between Pb2+ and SCN− was stronger than that between Pb2+ and I−. The space charge limited current and time-resolved photoluminescence results demonstrated a decrease in the trap density of the perovskite after being doped with SCN−; therefore, the doping process mitigated the defects of QDs, thereby increasing their optical performance, and further enhanced the bonding energy of Pb－X and crystal quality of QDs, thereby improving the stability of perovskite structure. Therefore, the photoluminescence quantum yield (PLQY) of the SCN-CsPbI3 QDs exceeded 90%, which was significantly higher than that of pristine QDs (68%). The high PLQY indicates low trap density of QDs, which is attributed to a decrease in the defects. Furthermore, the SCN-CsPbI3 QDs exhibited remarkable water-resistance performance, while maintaining 85% of their initial photoluminescence intensity under water for 4 h, whereas the undoped samples suffered complete fluorescence loss due to the phase transformations caused by water molecules. The SCN-CsPbI3 QDs photodetector measurements demonstrated a broad band range of 400–700 nm, along with a responsivity of 90 mA∙W−1 and detectivity exceeding 1011 Jones, which were considerably higher than the corresponding values of the control device (responsivity: 60 mA∙W−1 and detectivity: 1010 Jones). Finally, extending the doping of SCN− into CsPbCl3 and CsPbBr3 QDs further enhanced their optical properties on a significant scale.

Key words: Inorganic halide perovskite, Quantum dot, Doping, Stability, Photodetector