Molecular Weight Dependence of the Morphology in P3HT:PCBM Solar Cells
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- 作者：Feng Liu ; Dian Chen ; Cheng Wang ; Kaiyuan Luo ; Weiyin Gu ; Alejandro L. Briseno ; Julia W. P. Hsu ; Thomas P. Russell
- 刊名：ACS Applied Materials & Interfaces
- 出版年：2014
- 出版时间：November 26, 2014
- 年：2014
- 卷：6
- 期：22
- 页码：19876-19887
- 全文大小：727K
- ISSN：1944-8252
文摘
In polymer-based photovoltaic devices, optimizing and controlling the active layer morphology is important to enhancing the device efficiency. Using poly(3-hexylthiophene) (P3HT) with well-defined molecular weights (MWs), synthesized by the Grignard metathesis (GRIM) method, we show that the morphology of the photovoltaic active layer and the absorption and crystal structure of P3HT are dependent on the MW. Differential scanning calorimetry showed that the crystallinity of P3HT reached a maximum for intermediate MWs. Grazing-incidence wide-angle X-ray diffraction showed that the spacing of the (100) planes of P3HT increased with increasing MW, while the crystal size decreased. Nonlinear crystal lattice expansions were found for both the (100) and (020) lattice planes, with an unusual 蟺鈥撓€-stacking enhancement observed between 50 and 100 掳C. The melting point depression for P3HT, when mixed with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and, hence, the Flory鈥揌uggins interaction parameter depended on the MW. PCBM was found to perturb the ordering of P3HT chains. In photovoltaic devices, P3HT with a MW of 鈭?0K showed the best device performance. The morphologies of these blends were studied by grazing-incidence small-angle X-ray scattering (GISAXS) and resonant soft X-ray scattering. In GISAXS, we observed that the low-molecular-weight P3HT more readily crystallizes, promoting a phase-separated morphology.