A Comparison Study between Coupled and Non-coupled Systems of Poly(3-hexylthiophene) and Fullerene-C60 for the Application of Organic Solar Cells

Abstract

Organic solar cell technology has become one of the fastest growing areas of polymer science due to the world's need for clean, renewable energy. Some of the highest power efficiencies for organic solar cells have been observed in solar cells where a heterogeneous mixture of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) have been used as the active layer. A process called thermal annealing has been used to give high crystallinity for P3HT, improving light absorption and charge transport, but increasing segregation with the electron acceptor PCBM. In the study, the electron donor P3HT was coupled to fullerene-C60. A blend of P3HT and coupled product was compared to a completely non-coupled system to see if there was improvement in the overall efficiency of the organic solar cells. P3HT was synthesized and successfully coupled to fullerene-C60 based on analysis with GC/MS, HPLC, FTIR, and NMR spectroscopy. Synthesized P3HT was found to have only 79% regioregularity and average molecular weights under 3300 Da. The coupled materials were found to have a lower conjugation than the pure P3HT due to disruption to coplanarity by steric hindrance. Through analysis with DSC and TEM, it was discovered that the synthesized coupled material had a negative effect on the P3HT's ability to crystallize in comparison to pure P3HT and the P3HT/C60 blend. Based on power efficiency tests, fabricated solar cells containing the P3HT/coupled material blend were exponentially less efficient than the non-coupled blend of P3HT/C60.