Thickness dependence of the efficiency of polymer:fullerene bulk heterojunction solar cells

We study the thickness dependence of the performance of bulk heterojunction solar cells based on poly[2-methoxy-5-(3('),7(')-dimethyloctyloxy)-1,4-phenylenevinylene] as electron donor and [6,6]-phenyl C-61 butyric acid methyl ester as electron acceptor. Typically, these devices have an active layer thickness of 100 nm at which only 60% of the incoming light is absorbed. Increasing device thickness results in a lower overall power conversion efficiency, mainly due to a lowering of the fill factor. We demonstrate that the decrease in fill factor and hence device efficiency is due to a combination of charge recombination and space-charge effects

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

Light intensity dependence of open-circuit voltage of polymer: fullerene solar cells

The open-circuit voltage V-oc of polymer:fullerene bulk heterojunction solar cells is investigated as a function of light intensity for different temperatures. Devices consisted of a blend of a poly(p-phenylene vinylene) derivative as the hole conductor and 6,6-phenyl C-61-butyric acid methyl ester as the electron conductor. The observed photogenerated current and V-oc are at variance with classical p-n junction-based models. The influence of light intensity and recombination strength on V-oc is consistently explained by a model based on the notion that the quasi-Fermi levels are constant throughout the device, including both drift and diffusion of charge carriers. (C) 2005 American Institute of Physics