Chemical engineering in the electronics industry: progress towards the rational design of organic semiconductor heterojunctions

Abstract

We review the current status of heterojunction design for combinations of organic semiconductor materials, given its central role in affecting the device performance for electronic devices and solar cell applications. We provide an emphasis on recent progress towards the rational design of heterojunctions that may lead to higher performance of charge separation and mobility. We also play particular attention to the role played by computational approaches and its potential to help define the best choice of materials for solar cell development in the future. We report the current status of the field with respect to such goals. Introduction Developments in electronic devices over the past 50 years have revolutionized the way we conduct our daily lives, including the use of organic electronics in cell phones, display technologies and sensors, and ultra-fast processors that have improved the speed of computers in ways unimaginable a generation ago. For example, cell phone subscriptions worldwide passed 5 billion customers in 2010. The electronics industry is a major contributor to the global economy, valued at more than $300 billion in 2010 [1]. Chemical engineering in the semiconductor industriesChemical Engineers have played a strong role in the development of semiconductor materials and processing. Indeed, the American Institute of Chemical Engineers reports that $15% of graduating BS chemical engineers are employed in the electronics industries each year [2]. This is typically the second or third highest percentage destination behind chemicals ($25%), similar to fuels (12-20%), and above foods and pharmaceutical employment. At the PhD level, employment of chemical engineers by the electronics industry is around 20-30%, vying for the most popular destination with chemicals. The attraction of hiring chemical engineers in the electronics industry is clear: Many fabrication processes and materials design issues require a deep understanding of the underlying chemistry, physics and mathematics, and especially of thermodynamic and kinetic processes coupled to chemical reactions and reactor design that are the hallmark of a classically trained chemical engineer. Chemical engineers are trained to understand and apply physical and chemical concepts over extensive orders of magnitude in length-scale (and often time-scale). For example, understanding the atomic-level (sub-nm) details of charge absorption and separation, the multi-nanometer concepts of phase segregation or charge diffusion, and macroscopic (meter-scale) aspects concerning highthroughput processes such as the roll-to-roll processing of organic thin film devices.The interplay between chemical engineering and nanotechnology/electronics is likely to strengthen in the years ahead. For example, the focus of many modern chemical engineering departments is increasingly at the molecular scale; hence, nanotechnology and molecular-scale processing profitably draw upon the educational training of a chemical engineer. The tradition of chemical engineers in the energy indu...

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“…In fact, they are designed and constructed to have multiple interfaces in the same device with regions of the constituent materials intermixed at distances on the same order of magnitude as, or lower than, the diffusion length of the electronic excitations induced in the polymer moiety of the device. 2,3 Among BHJs, blends of regioregular poly(3-hexilthiophene) (rr-P3HT) and fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) are the most studied, 4 and for such blends, a power conversion efficiency of ≳5% was demonstrated. 5 Excitons created in the π-conjugate P3HT polymer dissociate into electron−hole pairs at the interface with PCBM, and then electrons migrate into the PCBM molecular crystal, leaving holes in the P3HT polymer.…”

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