Development of high efficiency bulk heterojunction organic solar cell and hydrogen fuel cell.

摘要

With the urgency to conserve finite fossil fuels and control the carbon release within the framework of Kyoto agreement regarding global warming effect, the society shows great interest for the renewable energy. Varieties of energy generation devices using renewable energy sources are then created. However, most of the technologies are still at early stage and the applications of these devices are limited due to their relatively low efficiency and high cost. For bulk heterojunction (BHJ) solar cell, the disordered morphology within the active layer for conventional BHJ solar cell construction significantly prevents the free movement of charge carriers, leading to low short circuit current and power conversion efficiency. In this thesis, a novel approach that introduces polystyrene that organizes the poly(3-hexylthiophene) (P3HT) into columnar phases decorated by [6,6]-phenyl C61-butyric acid methyl ester (PCBM) at the interface is presented. This structure represents a realization of an idealized morphology of an organic solar cell, in which, both exiciton dissociation and the carrier transport are optimized leading to increased power conversion efficiency. This feasibility of this idea was first tested by Molecular Dynamics (MD) simulations and then experimentally realized by optimization of ratios between P3HT, PS and PCBM. Columnar structure inside the polymer blends thin film was observed under TEM cross section measurement and the power conversion efficiency was indeed increased by 30% by constructing this specific structure inside active layer of BHJ solar cell. For polymer electrolyte membrane (PEM) fuel cell, the utilization of expensive platinum (Pt) catalysts limits the cost efficiency while the poisoning effect of Pt catalyst by the impurities in reforming hydrogen gas shortens the lifetime of the fuel cell. In this thesis, thiol-stabilized gold nanoparticles are synthesized through classic two-phase method and a monolayer of as prepared gold nanoparticles is deposited onto the surface of Nafion membrane by Langmuir-Blodgett (LB) trough. X-ray reflectivity (XRR) determines the thickness of the monolayer and the fuel cell performance results show that the monolayer deposition of gold nanoparticles could not only enhance the output power of PEM fuel cells significantly (up to 80%) but also increase the tolerance to the impurities in hydrogen gas, which is probably due to the active perimeter sites at the interface of gold and NafionR membrane support proven by output gas analysis. Further research shows that the activity of this deposited layer is a strong function of surface pressure that's applied for nanoparticles deposition, which indicates the important of direct contact between nanoparticles and membrane support. Meanwhile, similar construction of GO or rGO monolayer onto membrane surface can also greatly increase the output power of PEM fuel cells with even lower cost than the application of gold nanoparticles, which is mainly due to the enhanced ion conductivity for GO deposition and enhanced electron conductivity for rGO deposition.