So why disordered materials? Arguing from an application based (=engineer) point of view, disordered materials are usually easier and cheaper to be manufactured than (single or poly) crystalline ones. Looking at organic semiconductors, such as conjugated polymers or fullerene derivatives (“bucky balls”): they are soluble and can thus be deposited from the liquid phase – e.g., by printing (offset, inkjet, you name it). The vision for the so called plastic electronics is to print circuits and devices on flexible substrates. This can be done at room temperature (low energy) and ideally with roll-to-roll processes (high throughput). Sounds good, eh?
Well, there are some drawbacks in terms of the application… though not for researchers;-) Printing semiconductors usually leads to rather disordered films, which have very low charge carrier mobilities as compared to Silicon and other inorganic semiconductors, and are thus not suitable for high-frequency applications. However, for photovoltaic devices, the low mobilities are not that much of a drawback. That said, organic solar cells are still at below 7% power conversion efficiencies… for very small areas. Single crystalline Silicon, on the other hand, sees already above 20% for modules.
In my opinion, while organic solar cells probably never reach the performance of these Silicon devices – which might limit their suitability for rooftop applications – there is still a good chance to get printed low cost photovoltaic modules on flexible substrates with good energy balances. A prerequisite for achieving this goal is to do not only trial-and-error device development, but also fundamental research of the properties of disordered materials.
Speaking of which, from the point of view of basic research (physicist, o brother, where art thou), disordered materials are just… complex and very interesting… beautiful. So we just need the applications as an excuse to do what we like to do in any case;-)