Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands.
ACS Nano. 2012 Oct 23;6(10):8983-8. doi: 10.1021/nn303058u. Epub 2012 Sep 14.
Organic semiconductors are of great interest for application in cheap and flexible solar cells. They have a typical absorption onset in the visible. Infrared light can be harvested by use of lead-chalcogenide quantum dot sensitizers. However, bulk-heterojunction solar cells with quantum-dot sensitizers are inefficient. Here we use ultrafast transient absorption and time-domain terahertz spectroscopy to show that charge localization on the quantum dot leads to enhanced coulomb attraction of its counter charge in the organic semiconductor. This localization-enhanced coulomb attraction is the fundamental cause of the poor efficiency of these photovoltaic architectures. It is of prime importance for improving solar cell efficiency to directly photogenerate spatially separated charges. This can be achieved when both charges are delocalized. Our findings provide a rationalization in the development of photovoltaic architectures that exploit quantum dots to harvest the near-infrared part of the solar spectrum more efficiently.
有机半导体在廉价、灵活的太阳能电池中有很大的应用兴趣。它们在可见光范围内有典型的吸收起始。通过使用铅-硫属量子点敏化剂可以收集红外光。然而，具有量子点敏化剂的体异质结太阳能电池效率不高。在这里，我们使用超快瞬态吸收和时域太赫兹光谱来表明，量子点上的电荷定位导致其在有机半导体中的反电荷的库仑吸引力增强。这种定位增强的库仑吸引力是这些光伏结构效率低下的根本原因。直接光生空间分离电荷对于提高太阳能电池效率至关重要。当两个电荷都离域时，就可以实现这一点。我们的发现为开发利用量子点更有效地收集太阳光谱近红外部分的光伏结构提供了合理化解释。
