Semiconducting Polymers and Small Molecules for Transistors and Solar Cells
Understanding the impact of both the organic semiconductor design and processing conditions, on both molecular conformation and thin film microstructure is essential in achieving the required optical and electrical properties of organic electronic devices. For example, the charge carrier mobility in an organic field effect transistor can be significantly increased through appropriate optimization of the semiconductor molecular conformation and self-assembly. These aspects will be explored with an indacenodithiophene polymer as a case study. Organic solar cell efficiencies are currently increasing rapidly based on organic bulk heterojunction devices fabricated from solution. During this period, the structural diversity of semiconducting donor polymers for solar cells has increased dramatically, enabling accelerated development of bulk heterojunction (BHJ) organic solar cells based on polymer donor materials and molecular fullerene derivatives. However both the fullerenes, and the low bandgap polymers typically suffer from low absorption coefficients due to weak oscillator strength. Our approach has been to use P3HT as a p-type hole acceptor, and design highly absorbing, low-bandgap n-type small molecules to replace fullerenes. These fullerene acceptors not only have weak absorption, but also poor tunability of absorption over the longer wavelengths of the solar spectrum; morphological instability in thin film blends over time; high synthetic costs and limited scope for synthetic control over electronic and structural properties. For these reasons, we have developed new, synthetically simple electron acceptor materials, based on rhodanine end groups, which have much larger absorption coefficients than fullerenes, coupled with high lying LUMO energy levels, to maximize cell voltages. In BHJ devices with P3HT donor polymer, the rhodanine molecules were demonstrated to outperform all fullerenes.
Tuesday, March 11, 2016
11:00 am – 12:00 pm