有機光伏材料之光電性質研究

Abstract

本研究主要為探討有機-無機半導體材料混摻構成之光伏元件的基礎光電性質與元件結構設計，由於奈米材料具有獨特的量子效應與表面物理結構，因此當奈米結構的半導體與導電高分子混摻形成薄膜後，其介面間的反應以及載子的產生、傳導、以及結合等物理性質將是一個值得探討的主題。 由於高分子材料成型性良好且製程簡單，因此搭配奈米粒子、奈米柱、奈米線等作為混摻的對象將有助於材料受光激發後產生的光電流效率以及傳輸的途徑，藉由控制奈米粒子的形態與尺寸可使得受光激發後的Exciton在擴散距離內即被分離成帶電電荷，而分子鏈的長短亦會影響Exciton能量的轉移與載子的傳輸，鏈與鏈的交互作用與交錯排列將可使帶電載子有連續性的傳導途徑◦

In this thesis, the charge separation and transport efficiency of inorganic/organic hybrid photovoltaic material were studied. The unique quantum confinement and shape manipulation characteristic for nanoparticle can be utilized to fabricate photovoltaic device with special physical properties not observed in traditional silicon-base inorganic cell. Initial studies include optical properties of pristine MEH-PPV conducting polymer. Variation of the polymer concentration and molecular weight show that the PL and absorption spectrum red-shift with high solution concentration and high molecular weight. Exciton decay time is also influenced by interchain interaction. The interchain interaction could result in energy transfer and PL quench. We also study temperature dependence of blend system in dynamic and static measurements. The experiments show that at same temperature, PL spectra have red shift as the CdSe nanoparticle concentration increase in the polymer matrix. At low temperature, the absorption and PL spectrum also shift to long wavelength. These results can explain that the stacking order increase at low temperature and the increase in CdSe nanoparticle concentration also have similar effect. These phenomenons are interpreted by the increase in effective conjugated length. Effective conjugated length decreases while the temperature increases due to chain torsional motion. Therefore, increase in CdSe nanoparticle concentration would extend the effective conjugated length, and result in different Vibronic level transition decay time. Thin films photovoltaic device with varied CdSe nanoparticle concentration have significant improvement over pristine MEH-PPV device. This is consistent with charge separation efficiency improvement at high nanoparticle concentration. High nanoparticle concentration not only provides charge separation pathway, but also support efficiency electron transfer route. Also the short circuit current is proportional to CdSe concentration.