Center for Functional Nanomaterials Seminar

Organic photovoltaics (OPVs) are of interest for their potential in the production of low-cost solution-processed solar cells. State-of-the-art OPVs have achieved power conversion efficiencies (PCEs) of 4-6%. However, to attain efficiencies approaching 10% which is necessary for OPVs to compete with conventional solar cells requires further understanding of the structure-property between semiconducting materials and their photovoltaic performance. In the first part of my presentation, I will talk about the concept of dielectric modification for improved charge separation. As one of the limits for OPVs is the low dielectric constant (~ 3) of organic semiconductor, we have shown that the dielectric constant of P3HT can be increased by simple chemical modification. As proof-of-concept, we have demonstrated that the increase of dielectric constant can lead to the improvement of photovoltaic performance in P3HT/CN-PPV bilayer devices. In the second part of my presentation, I will talk about our efforts on developing solution-processable molecular donors (small molecules, dendrimers and oligomers) for photovoltaic applications. In contrast to polymeric systems that intrinsically display large structural variations, conjugated small molecules and oligomers possess well-defined structure and show a strong tendency to self-assemble into ordered crystalline domains with better charge transport properties. Towards this goal, we have rationally designed a series of platinum-acetylide oligomers that show broad absorption, strong tendency to self-assemble and good hole mobilities. When blended with fullerenes, bicontinuous morphology was obtained for the photoactive layer, which ensures efficient charge separation and high power conversion efficiencies. Our work suggests that well-defined oligomers with desirable light-absorbing and self-assembly properties have potential for use in OPVs.