The Development of Nano-Structured Heterojunction Polymer Solar Cell(I)
|關鍵字:||導電高分子;奈米棒;表面電漿奈米顆粒;光伏電池;donor–accepter polymer;dye;aligned nanorods;surface plasmonic nanoparticles;photovoltaic devices|
Solution-processed conjugated organic materials combine the electronic properties of semiconductors with the high processability of polymeric materials, allowing them to be cast using wet-processing techniques such as spin casting, dip coating, ink-jet printing, screen printing, and micro-molding. These techniques are enormously attractive for producing low-cost, flexible, large-area photovoltaic cells that are suitable for commercial applications in optoelectronics technologies. Our main objective for this project is to construct high-efficiency bio-inspired conjugated polymer heterojunction photovoltaic cells incorporating (i) donor–acceptor polymers presenting side chain-tethered dye or electron withdrawing moieties, (ii) ordered and bandgap-engineered nanorods (NRs), and (iii) metal nanoparticles (NPs) exhibiting surface plasmonic effects. The principal idea behind the design of these photovoltaic cells is that the heterojunctions between the ordered NRs and conjugated polymers will be formed in such a way that the inter-rod distance will be on the same order of magnitude as the diffusion length of the excitons. First, a high degree of absorption of solar energy will be accomplished using polymers consisting of a conjugated main chain, absorbing wavelengths in middle of the visible light spectrum, and side-chain-tethered dye or electron-withdrawing moieties, absorbing in the near-infrared or ultraviolet region. We aim to synthesize polythiophenes or polyfluorenes tethered to transition metal-based dyes, such as ruthenium(II) bipyridine complexes and platinum(II) diimine dithiolate complexes, that will absorb more than 30% of the solar energy, much higher than that (20%) adsorbed by such conjugated polymers alone. Second, monolayered polymer thin films incorporating aligned nanorods will be obtained by two steps. The first step involves in mixing pyridine-modified NRs and a polymer in pyridine; the NRs become distributed selectively on the side chains of the polymer as a result of their preference for experiencing polar interactions. Then, the nanorods in these composite films became aligned after they experienced external fields such as electric or magnetic field at elevated temperature. Alternatively, anodic aluminum oxide (AAO) templates can be used to fabricate vertical composite nanorods consisting of polymer and nanoparticles. Third, the effect that incorporating metal nanoparticles has on the plasmonic enhancement of polymer/NPs or NRs bulk heterojunction systems will examined. Because the dipole-allowed photogeneration of excitons in the active layer should scale with the square of the electric field, we hypothesize that enhancing the local electromagnetic field through the inclusion of surface plasmon-active materials such as metal nanoparticles will enhance the degree of photogeneration of excitons in the conjugated polymers and, to a lesser degree, in nanorods. Moreover, in the tandem cell structure, we will adopt an inverted structure using a multiple-wavelength absorbing, low bandgap polymer/fullerene composite. With our proposed cell architecture, the probability of diffusion of excitons to the heterojunction interfaces will be relatively high and their separation relatively more complete. Moreover, the presence of the NRs will provide direct pathways for the electrons to move through the NRs toward the cathode, while the conducting polymers will serve as channels for holes to move to the anode once the excitons have dissociated at the interfaces. Having the electrons and holes travel along their independent paths to their respective electrodes will decrease their chance of recombination and, thereby, increase the cell’s power conversion efficiency. By combining enhanced optical absorption of donor-acceptor conjugated polymer, aligned semiconductor nanorods device architecture, surface plasmonic effect of nanoparticles and tandem cell structure, we believe that we can achieve power conversion efficiency of at least 8% for the proposed heterojunction poymer/nanorod solar cells in three years.
|Appears in Collections:||Research Plans|