Self-assembly of polymers and small molecules for photovoltaics application

Abstract

Solar energy is one of the most promising energy sources of the future with depleting amount of fossil fuels, and organic photovoltaic (OPV) is among the cheapest in terms of materials and processing methods. However, the performance of OPV is largely dependent on the morphology of the photoactive layer. In this project, morphological control of the photoactive layer has being achieved for P3HT polymer and PTCDI-C13H27 small molecule with the addition of poor solvent. Upon introduction of poor solvent, favorable π-stacking can be induced from the changes in solubility to create one-dimensional (1-D) structure with enhanced crystallinity. Using this approach, P3HT nanofibers were constructed and devices based on this P3HT:PCBM blend obtained an increment in PCE from 0.9% to 2.3% without any post production treatment such as thermal annealing. In addition, different dimensions of PTCDI 1-D structure were also obtained using different methods of poor solvent addition. By controlling the amount of nucleation sites created and the subsequence interactions at each site, the width and length of the PTCDI 1-D structure can be controlled. The width of the PTCDI-C13H27 structures range from 20 μm to 70 nm with length ranging from 0.1 cm to 2 μm.