高分子/低能階差半導體奈米粒子混摻太陽能電池系統之開發以及導入奈米粒子作為高分子太陽能電池之添加劑

Abstract

導電高分子與奈米粒子混摻所製作成的元件具有好的物理以及熱穩定性質，在此研究的第一及第二部分當中，我們試圖開發新的混摻太陽能電池系統，分別是用 Bi2S3 奈米桿或 Cu2S 奈米粒子和導電高分子P3HT混摻，此兩種奈米材料的能階差都小於1.8電子伏特，屬於低能階差的半導體材料，對於光伏元件的吸光將有顯著的幫助。我們首先利用化學方法合成出兩種奈米粒子，並且對其基本性質進行分析，選定穩定的合成條件之後將奈米粒子和導電高分子P3HT進行混摻，混摻薄膜的光學以及電學性質也將被有系統的分析，最後，我們將兩者分別製作成太陽能電池，P3HT / Bi2S3 系統所能達到的能量轉換效率為0.06%，P3HT / Cu2S 系統所能達到的效率則為0.1%，此研究開發出了兩個對環境無害，且低成本的太陽能電池混摻系統。 本研究的第三部份為將少量奈米粒子的加入P3HT / PCBM 系統當中作為添加劑，以提升其能量轉換效率，我們首先選用大小約4-5奈米的硫化銅奈米粒子作為添加劑，並且著重於利用製程參數的改變使能量轉換效率的最佳化，包括奈米粒子濃度，以及熱處理條件等，我們最後得到能量轉換效率由原先標準P3HT / PCBM 試片的3.7%，在加入0.05 毫克 / 毫升添加劑後，增加至4.3 %，增加百分比約16%。我們合理的去對這個效率增加的原因進行假設，並試圖去尋找相關佐證，最後發現加入奈米粒子作為添加劑將會改變薄膜的表面型態，進而提升其元件表現。原子力顯微鏡以及掠角X光散射分析提供我們薄膜在加入添加劑後的型態變化，在添加劑的作用下，P3HT以及PCBM之間更大的接觸面積，更細微的結構，以及更緊密的交互作用都造成能量轉換效率的增加，最後，我們選用其他大小相似的奈米粒子如硒化鎘(CdSe)作為添加劑，發現其對於元件效率的表現增加是相似的，也證明我們的假設，加入適量的奈米粒子對於P3HT / PCBM系統的表面型態以及能量轉換效率將有佳化的作用。

Polymer photovoltaic devices have attracted considerable interest over the past decade owing to the advantages of low-cost, low weight, solution fabrication process, large area and flexibility. The hybrid materials made from conducting polymers and inorganic semiconducting nanocrystals have potential application in solar cell due to their physical stability. In the first part and second part of our study, we have tried to develop new systems of polymer solar cell based on either P3HT / Bi2S3 nanorods or P3HT / Cu2S nanoparticles hybrid. Nanocrystals of Bi2S3 and Cu2S are environmental friendly and low cost. Both nanocrystals have low band gap (lower than 1.8 eV) which show potentials in sun light harvesting. The synthesis and characterization of Bi2S3 nanorods and Cu2S nanoparticles were conducted. Additionally, the properties of hybrid films of P3HT / Bi2S3 nanorods or P3HT / Cu2S nanoparticles were performed. TypeⅡ band alignment between P3HT and low band gap nanocrystals gives chances for charge separation at the interfaces. The photovoltaic devices based on P3HT / Bi2S3 and P3HT / Cu2S hybrid exhibit power conversion efficiency of 0.06 % and 0.1% respectively under AM 1.5, 100 mW/cm2 illumination. In the third part of this research, we incorporated Cu2S nanoparticles as an additive to improve the power conversion efficiency of P3HT / PCBM system. A 16 % increase in power conversion efficiency (from 3.7 % to 4.3 %) has been achieved by incorporating 0.05 mg ml-1 Cu2S nanoparticles in the P3HT / PCBM active layer under proper thermal treatment. The additive induced morphology variations of active layer were analyzed by AFM and grazing incidence X-ray diffraction. The results reveal the Cu2S nanoparticles hinder the growth of PCBM clusters and compress the crystallization of P3HT during thermal treatment. The smaller crystal dimension of P3HT and reduced size of PCBM clusters result in finer structures, larger interfaces, and closer interconnecting between P3HT and PCBM which enhance the power conversion efficiency. Other nanoparticles such as CdSe with similar size to Cu2S also lead to the similar effect. We therefore conclude that the incorporation of adequate amount of nanoparticles in the active layer is an effective strategy to improve the performance of P3HT / PCBM solar cells.