利用無規整度聚3-己基噻吩改善太陽能元件效率穩定度

Abstract

有機太陽能電池研究領域中，高規整度聚(3-己基噻吩)是目前研究最為深入的材料，其太陽能電池轉換效率約為5%。然而，如何提升太陽能電池轉換效率的穩定度，一直以來是此領域的挑戰。本研究中，為了提升太陽能電池轉換效率的穩定度，我們研究混摻不同規整度聚(3-己基噻吩)與[6,6]-苯基C60-丁酸甲酯的光學性質、型態以及太陽能電池轉換效率的穩定度，發現添加少量低規整度聚(3-己基噻吩)可以有效提升太陽能電池轉換效率的穩定度(高規整度與低規整度聚(3-己基噻吩)重量比為95:5)。低規整度聚(3-己基噻吩)的非結晶結構與[6,6]-苯基C60-丁酸甲酯具有良好的相溶性，可以避免[6,6]-苯基C60-丁酸甲酯隨時間產生聚集。我們使用原子力顯微鏡鑑定薄膜的表面，發現加入少量低規整度聚(3-己基噻吩)後的表面粗糙度並沒有隨時間明顯的增加。另外，從X光散射與光學顯微鏡的量測中，證實混摻低規整度聚(3-己基噻吩)可以延緩[6,6]-苯基C60-丁酸甲酯隨時間產生聚集形成穩定的主動層結構。本研究結果顯示，加入少量低規整度聚(3-己基噻吩)可以有效避免[6,6]-苯基C60-丁酸甲酯隨時間產生聚集，形成穩定的主動層結構，因此提升太陽能電池轉換效率的穩定度。

Regioregular poly(3-hexylthiophene) (P3HT) has been the most-studied conjugated polymer for fabricating bulk heterojunction organic solar cells with an acceptable power-conversion efficiencies up to approximately 5%. However, a key challenge to the commercialization of organic solar cells is the achievement of power conversion efficiency stability. In this study, we investigated the optical properties, the photovoltaic performance, and the morphology of ternary blends consisting of regioregular poly (3-hexylthiophene) (c-P3HT), regiorandom P3HT (a-P3HT), and [6,6]-Phenyl C60-butyric acid methyl ester (PCBM). The photovoltaic cells are fabricated by inverted device structure. We found that the stability of power conversion efficiency can be significantly improved by mixing c-P3HT with a small amount of a-P3HT (c-P3HT:a-P3HT = 95:5). We attribute such an improvement to the amorphous nature of a-P3HT that prevents PCBM from severe aggregation with time. We utilized atomic force microscopy (AFM) to characterize the surface of thin films and found that thin films with a-P3HT show less increase in surface roughness with time compared to neat c-P3HT film. In addition, grazing incidence small-angle X-ray scattering (GISAXS) demonstrates that the aggregation rate of PCBM is retarded when a-P3HT is added, which can macroscopically be confirmed by optical microscopy images where large PCBM crystals are seen after a longer annealing time with the presence of a-P3HT. These results suggest that the phase separation can be suppressed by introducing a-P3HT in active layer and thus stable morphologies can be achieved and the stability of solar cells is enhanced.