Peng Qiang, Park Kuyson, Lin Tong, Durstock Michael, Dai Liming
Department of Chemical and Materials Engineering, School of Engineering and Department of Chemistry and UDRI, University of Dayton, 300 College Park, Dayton, OH 45469, USA.
J Phys Chem B. 2008 Mar 13;112(10):2801-8. doi: 10.1021/jp7105428. Epub 2008 Feb 19.
A class of new conjugated copolymers containing a donor (thiophene)-acceptor (2-pyran-4-ylidene-malononitrile) was synthesized via Stille coupling polymerization. The resulting copolymers were characterized by 1H NMR, elemental analysis, GPC, TGA, and DSC. UV-vis spectra indicated that the increase in the content of the thiophene units increased the interaction between the polymer main chains to cause a red-shift in the optical absorbance. Cyclic voltammetry was used to estimate the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) and the band gap (Eg) of the copolymers. The basic electronic structures of the copolymers were also studied by DFT calculations with the GGA/B3LYP function. Both the experimental and the calculated results indicated an increase in the HOMO energy level with increasing the content of thiophene units, whereas the corresponding change in the LUMO energy level was much smaller. Polymer photovoltaic cells of a bulk heterojunction were fabricated with the structure of ITO/PEDOT/PSS (30 nm)/copolymer-PCBM blend (70 nm)/Ca (8 nm)/Al (140 nm). It was found that the open-circuit voltage (Voc) increased (up to 0.93 V) with a decrease in the content of thiophene units. Although the observed power convention efficiency is still relatively low (up to 0.9%), the corresponding low fill factor (0.29) indicates considerable room for further improvement in the device performance. These results provided a novel concept for developing high Voc photovoltaic cells based on donor-pi-acceptor conjugated copolymers by adjusting the donor/acceptor ratio.
通过Stille偶联聚合反应合成了一类新型的含供体（噻吩）-受体（2-吡喃-4-基亚甲基丙二腈）的共轭共聚物。通过1H NMR、元素分析、凝胶渗透色谱（GPC）、热重分析（TGA）和差示扫描量热法（DSC）对所得共聚物进行了表征。紫外可见光谱表明，噻吩单元含量的增加增强了聚合物主链之间的相互作用，导致吸光度发生红移。采用循环伏安法估算了共聚物的最低未占分子轨道（LUMO）和最高占分子轨道（HOMO）的能级以及带隙（Eg）。还通过使用GGA/B3LYP函数的密度泛函理论（DFT）计算研究了共聚物的基本电子结构。实验和计算结果均表明，随着噻吩单元含量的增加，HOMO能级升高，而LUMO能级的相应变化则小得多。制备了具有ITO/PEDOT/PSS（30 nm）/共聚物-PCBM共混物（70 nm）/Ca（8 nm）/Al（14 nm）结构的本体异质结聚合物光伏电池。发现随着噻吩单元含量的降低，开路电压（Voc）升高（高达0.93 V）。尽管观察到的功率转换效率仍然相对较低（高达0.9%），但相应较低的填充因子（0.29）表明器件性能仍有相当大的进一步提升空间。这些结果为通过调节供体/受体比例来开发基于供体-π-受体共轭共聚物的高Voc光伏电池提供了新的思路。
