| Abundant, scalable, environmentally-friendly organic photovoltaic (OPV) technology is increasingly promising in recent years. The power conversion efficiency (PCE) of OPVs has been raised to around 10%. However, this record efficiency is still far below the Shockley-Quasar limit of 22~27%. This dissertation introduces great research effort to improve the OPV device efficiency by understanding the device physics, and engineering the donor/acceptor interfaces as well as designing new device architectures. The research activities mainly focused on: 1) Understanding the physical mechanism of open circuit voltage in OPVs; 2) Optimizing the band offset between the donor and the acceptor by using ultrathin ferroelectric dipole layer between donor/acceptor interfaces; 3) Designing fullerene based Schottky-barrier junction structure to obtain large open circuit voltage of round 0.9 V; 4) Applying thermally-annealed bilayer heterojunction structure to improve OPV device performance and demonstrating the origin of the improvement is due to reduced bimolecular charge recombination loss; 5) Studying the ferromagnetism of model photovoltaic materials poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), which might open up another approach to improve P3HT:PCBM based organic solar cells by using external magnetic fields, and also might initiate the applications of multifunctional organic optoelectronics with integration of electronics, photonics, and magnetics. |
