Center for Functional Nanomaterials Seminar

Organic photovoltaics (OPVs) are the promising cost-effective alternative to the silicon-based solar cells. However, the efficiency of organic solar cells has to be enhanced for widespread applications. Further understanding the fundamental photovoltaic processes and exploring the new materials are needed to improve the performance of OPVs. In the first part of this talk, our work on singlet/triplet related photovoltaic processes in OPVs is introduced. We find that the singlet and triplet spin orientations of excited states (excitons, charge transfer states, polaron pairs) in conjugated organic materials lead to different dissociation and recombination processes, and consequently the different efficiency of photocurrent generation. As a result, the PV efficiency of bulk-heterojunction OPVs based on conjugated polymer MEH-PPV and fullerene derivative PCBM can be enhanced by optimizing the ratio of singlet/triplet excited states in the polymer. Furthermore, the magnetic field effect on photocurrent (MFP) measurement is found to be an effective way to study the singlet/triplet related PV processes in organic devices and a few examples are demonstrated in the talk. In the second part of this talk, the PV applications of two polymer-based hybrid material systems are introduced. Carbon Nanotubes (CNTs) are successfully applied as doping materials and transparent electrode in polymer-based PV cells. Upconversion fluorescence nanocrystals NaYF4:Yb, Er are doped into conjugated polymers and show the potential application as NIR photodetector.