P3HT-Based Solar Cells: Structural Properties and Photovoltaic Performance

Each year we are bombarded with B.Sc. and Ph.D. applications from students that want to improve the world. They have learned that their future depends on changing the type of fuel we use and that solar energy is our future. The hope and energy of these young people will transform future energy technologies, but it will not happen quickly. Organic photovoltaic devices are easy to sketch, but the materials, processing steps, and ways of measuring the properties of the materials are very complicated. It is not trivial to make a systematic measurement that will change the way other research groups think or practice. In approaching this chapter, we thought about what a new researcher would need to know about organic photovoltaic devices and materials in order to have a good start in the subject. Then, we simplified that to focus on what a new researcher would need to know about poly-3-hexylthiophene:phenyl-C61-butyric acid methyl ester blends (P3HT: PCBM) to make research progress with these materials. This chapter is by no means authoritative or a compendium of all things on P3HT:PCBM. We have selected to explain how the sample fabrication techniques lead to control of morphology and structural features and how these morphological features have specific optical and electronic consequences for organic photovoltaic device applications

Determining the optimum morphology in high-performance polymer-fullerene organic photovoltaic cells

This work was supported by the Engineering and Physical Sciences Research Council (grant number EP/I013288/1) and from the European Union Seventh Framework Programme under grant agreement 321305.The morphology of bulk heterojunction organic photovoltaic cells defines many of the device performance characteristics. Measuring the morphology is challenging due to the small length scales and low contrast between organic materials. Here we have utilised nanoscale photocurrent mapping, ultrafast fluorescence and exciton diffusion to observe the detailed morphology of a high performance blend. We show that optimised blends consist of elongated fullerene-rich and polymer-rich fibre-like domains which are 10-50 nm wide and 200-400 nm long. These elongated domains provide a concentration gradient for directional charge diffusion which helps extraction of charge pairs with 80% efficiency. In contrast, blends with agglomerated fullerene spheres show a much lower efficiency of charge extraction of ~45% which is attributed to poor electron and hole transport. Our results show that formation of narrow and elongated domains are desirable in bulk heterojunction solar cells.Publisher PDFPeer reviewe