Modification of nanomorphology in polymer/fullerene blends-route toward high efficiency polymer solar cells

Extensive research is going into polymer solar cells because of their advantage of ease of fabrication, low cost, ability to make large area devices and mechanical flexibility. Optimizing the morphology on a molecular level is essential for achieving high performance polymer solar cells. Optimal nanomorphology leads to optimized exciton dissociation efficiency which is determined by the donor/acceptor interface area and optimal charge transport efficiency through percolating pathways for carriers. In this presentation, we discuss three strategies to manipulate the nanomorphology of regioregular poly(3-hexylthiophene) (rr-P3HT): [6,6]phenyl-C61-butyric acid methyl ester (PCBM) blends viz. thermal annealing, solvent annealing and mixed solvent approach, all of which lead to improved photovoltaic performance. It has been shown that all the three strategies lead to better ordering of the P3HT domains and hence good polymer crystallinity. The effect of these strategies on the blend morphology, polymer crystallinity, absorption and charge carrier mobility will be discussed and will be related to the photovoltaic performance of the device.