Effects of Branched Side Chain on the Physical Properties and Solar Cell Performance of Polythiophene

• Main Authors: Jia-Yi Chu, 朱佳儀
• Other Authors: 童世煌
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/kqhz6c

碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 107 === Over the past decade, the polymer/fullerene-based organic solar cell has rapidly developed. In addition to the increase of power conversion efficiency (PCE) by adding additives or synthesizing new structure, the improvement of stability has also been a key issue for the organic solar cell. In this study, we synthesized poly(3-2-methylpentylthiophene) (P3MPT), a polythiophene with branched side chain and studied the morphology, thermal properties, and photovoltaic performance of P3MPT blended with different fullerene derivatives. The results are compared to those of the commonly used poly(3-hexylthiopene) (P3HT) with linear side chains to investigate the effects of side chain configuration. We found that P3MPT/PC61BM solar cells not only show a higher efficiency but can maintain the high efficiency much longer than the P3HT/PC61BM solar cells. Compared to P3HT/PC61BM systems, the size of domains extracted by the small-angle X-ray scattering (SAXS) profiles implies a more stable phase separated structure in P3MPT/PC61BM blends. We suggest that the branched side chains are bulkier than the linear side chains and thus can provide a higher steric hindrance, which causes more rigid side chains and backbones to slow down the phase separation rate between P3MPT and PC61BM. The higher glass transition temperature of P3MPT than that of P3HT was confirmed by differential scanning calorimetry (DSC). In addition, DSC and Wide-angle X-ray scattering show that the crystallization ability of P3MPT is lower than that of P3HT also due to the bulkier side chains. The higher glass transition temperature and the lower crystallization ability of P3MPT contribute to the superior long-term stability of P3MPT/PC61BM system.