Organic solar cells tuned by blending

Electrical engineers can finetune the energetics of rigid photovoltaics and transistors by blending different semiconducting materials. However, it's hard to apply this tuning protocol to the flexible class of carbon-based semiconductors. Schwarze et al. now show that continuous band energy tuning is indeed possible by varying the blend ratios of certain organic phthalocyanines and their fluorinated or chlorinated derivatives (see the Perspective by Ueno). They demonstrated the effect, which they attribute to quadrupolar interactions, in model solar cells.

Abstract

A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors.

Science 17 Jun 2016:
Vol. 352, Issue 6292, pp. 1446-1449
DOI: 10.1126/science.aaf0590

http://science.sciencemag.org/content/352/6292/1446

现代电子学的一个关键突破就是引入了能带结构工程，通过融合不同半导体来不断调整带隙和带边能量几乎可以设计出任意的电子势结构。而有机半导体中强局域化的电子态的阻碍了这种方法在这些材料中的应用。Schwarze等展示了一种迄今为止很大程度上忽视远距离库伦力相互作用的变通方法。由光电子能谱可以确认，与其卤化衍生物相混合，有机半导体晶体的电离能可以在大范围内实现连续可调。相应地，有机太阳能电池的光伏带隙和开路电压可以通过掺入一定比例的施主杂质实现连续可调。（Science DOI：10.1126/science.aaf0590）（新材料在线）