Flinders Institute for Nanoscale Science and Technology , Flinders University , GPO Box 2100, Adelaide SA 5001 , Australia.
ACS Appl Mater Interfaces. 2018 Dec 19;10(50):44163-44172. doi: 10.1021/acsami.8b16725. Epub 2018 Dec 5.
MoO is widely used in polymer-based organic solar cells as an anode buffer layer because of its high workfunction and formation of a strong dipole at the MoO/polymer interface facilitating charge transfer across the MoO/polymer interface. In the present work, we show that exposure of the MoO/polymer interface to moisture attracts water molecules to the interface via diffusion. Because of their own strong dipole, water molecules counter the dipole at the MoO/polymer interface. As a consequence, the charge transfer across the MoO/polymer will reduce and affect the charge transport across the interface. The outcome of this work thus suggests that it is critical to keep the MoO/polymer interface moisture-free, which requires special precautions in device fabrications. The composition of the MoO/P3HT:PCBM interface is analyzed with X-ray photoelectron spectroscopy and the depth profiling technique, neutral impact collision ion scattering spectroscopy. The results show that the concentration of oxygen increases upon exposure but leaves the oxidation state of Mo unchanged. The valence electron spectroscopy technique shows that the dipole across the MoO/P3HT:PCBM interface decreases even for short-time exposure to atmosphere because of the diffusion of water molecules to the interface. The far-ranging consequences for organic electronic devices are discussed.
MoO 广泛应用于基于聚合物的有机太阳能电池中作为阳极缓冲层，因为其高功函数和在 MoO/聚合物界面形成强偶极子，有利于电荷在 MoO/聚合物界面的转移。在本工作中，我们表明 MoO/聚合物界面暴露于水分会通过扩散将水分子吸引到界面。由于水分子自身具有很强的偶极子，它们会与 MoO/聚合物界面的偶极子相抗衡。因此，电荷在 MoO/聚合物中的转移会减少，并影响电荷在界面中的传输。这项工作的结果表明，保持 MoO/聚合物界面无水至关重要，这在器件制造中需要特别注意。使用 X 射线光电子能谱和深度剖析技术、中性冲击碰撞离子散射光谱分析了 MoO/P3HT:PCBM 界面的组成。结果表明，暴露后氧的浓度增加，但 Mo 的氧化态保持不变。价电子能谱技术表明，即使暴露于大气中很短时间，由于水分子向界面扩散，MoO/P3HT:PCBM 界面的偶极子也会减小。讨论了对有机电子器件的深远影响。
