Dipolar Molecular Capping in Quantum Dot-Sensitized Oxides: Fermi Level Pinning Precludes Tuning Donor-Acceptor Energetics

作者：Wang Hai I; Lu Hao; Nagata Yuki; Bonn Mischa; Canovas Enrique^*

来源：ACS Nano, 2017, 11(5): 4760-4767.

DOI：10.1021/acsnano.7b01064

• molecular dipole
• PbS quantum dots
• interfacial electron transfer
• Fermi level pinning sensitized system
• quantum dot-sensitized solar cells
• THz spectroscopy

Reducing the donor-acceptor excess energy (Delta G(ET)) associated with electron transfer (ET) across quantum dot (QD)/oxide interfaces can boost photoconversion efficiencies in sensitized solar cell and fuel architectures. One proposed path for engineering Delta G(ET) losses at interfaces refers to the tuning of sensitizer workfunction by exploiting QD dipolar molecular capping treatments. However, the change in workfunction per debye in QD solids has been reported to be similar to 20-fold larger when compared to the effect achieved in QD-sensitized architectures. The origin behind the modest workfunction tunability in QD-sensitized oxides remains unclear. Here, we investigate the interplay between QD dipolar molecular capping, interfacial QD-oxide ET rates, and QD workfunction in PbS QD/SnO2-sensitized interfaces. We find that interfacial QD-to-oxide ET is invariant to both the nature and strength of the specific QD dipolar capping treatment. Photoelectron spectroscopy reveals that the resolved invariance in ET rates is the result of a lack of QD workand hence Delta G(ET)) tuning, despite effective molecular dipolar capping. We therefore conclude that Fermi level pinning precludes tuning donor-acceptor energetics by dipolar molecular capping in strongly coupled quantum dot-sensitized oxides.

• 出版日期2017-5