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High Performance Organic Solar Cells with Controlled Morphology and Interfaces

2009년 9월 1일 15시 36분 14초
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목 15시 : 00분
공업화학 - Dye-Sensitized and Organic Solar Cells
저자 및
포항공과대학교 화학공학과, Korea
The device performance of organic photovoltaics (OPVs) is influenced much by the molecular and mesoscale structures of organic semiconductor films that determine their exciton generation and charge transport characteristics. In the operation of OPVs, charge separation from exciton and charge carrier transport are strongly dependent on the properties of two kinds of interface: interfaces between semiconductors and electrodes, where charge injection occurs from the semiconductor into the electrodes, and interfaces between donor and acceptor materials, where exciton separation takes place. Also, the molecular structure and morphology of the active layer seriously depend on the properties of the each interface. Here, several approaches for controlling interfaces and structures of semiconductor films are discussed. First, we controlled work function and surface energy of electrode (ITO) for HOMO level matching between electrode and active layer, and phase separation of active layer. Second, by using a template, we fabricated poly (3-hexylthiophene) nano rod / C60 ordered bulk heterojunction device. Increasing interfacial contact area between donor and acceptor caused the enhanced device performance. Third, by modification of end functional group of P3HT, we controlled the miscibility between P3HT/PCBM, and domain size of each material. By optimizing the phase separation and morphology of active layer, we can achieve the efficiency, ~5% with fill factor 0.68. Finally, we demonstrate bulk heterojunction solar cells based on blends of preformed P3HT nanowires and PC61BM by using marginal solvent without any post treatment, and the morphology and photovoltaic properties were studied as a function of the P3HT nanowires’ aging time. Additionally, we have demonstrated an optimized morphology of the blend film using two separate steps: P3HT nanowire formation from mixed solvents and subsequent phase separation by low temperature annealing. With the help of interpenetrating nanowire structures, carrier mobility is dramatically increased and photovoltaic performance has been improved since the subsequent light absorption with reduced recombination loss of the carriers.