Organic Photovoltaics (OPVs)
Solar energy is one of the most promising candidates to replace the finite and non-renewable fossil fuel based energy sources that have also triggered global environmental concerns, including pollution and global warming. In order for photovoltaic devices, which convert sunlight into electricity, to be broadly accepted and applied, the cost per unit of energy output must be significantly reduced to be comparable with that of traditional resources. Organic photovoltaic devices (OPVs), especially polymer based OPVs, have great potential for cost reduction due to the solution processability of polymers, which is amenable to large-area high-throughput roll-to-roll processes. Currently, the major hurdles for the commercialization of OPVs are their relatively low power conversion efficiencies and environmental instability. Overcoming these drawbacks requires better understanding of OPV physics and electronic processes, novel materials design and synthesis, precise morphology control and optimized device geometry, all of which is derived from the interplay of chemistry, physics, material science and engineering as shown in the figure.
Our research is focused on these three major areas:
- Design and synthesis of novel conjugated polymers with reduced bandgap energy, optimized energy level alignment and high crystallinity. The aim is to satisfy the major requirements for ideal donor materials in OPVs: enhanced sunlight absorption, efficient charge separation, maximum attainable photovoltage and high conductivity.
- Application of block copolymer self-assembly strategies and nanotechnologies including nano-imprinting and photo-lithography to realize the so-called ordered bulk heterojunction (BHJ) morphology in the OPV active layer, which could greatly enhance charge separation and collection leading to higher photocurrent.
- Device fabrication/engineering, testing and, optimization that includes, to list a few, morphology optimization, surface treatment, alternative electrodes replacing ITO, novel device geometry such as inverted cells and tandem cells.
We also perform strong collaboration with theoreticians, spectroscopists, physicists and engineers for a better understanding of the electronic processes and mechanisms of OPVs, which in turn provides guidance for further material design and device optimization.
We gratefully thank the following sponsors for generously supporting our research: