Influence of Fluorination and Molecular Weight on the Morphology and Performance of PTB7:PC71BM Solar Cells

被引:39
作者
He, Xiaoxi [1 ]
Mukherjee, Subhrangsu [2 ]
Watkins, Scott [3 ]
Chen, Ming [3 ]
Qin, Tianshi [3 ]
Thomsen, Lars [4 ]
Ade, Harald [2 ]
McNeill, Christopher R. [5 ]
机构
[1] Univ Cambridge, Cavendish Lab, Cambridge CB3 0HE, England
[2] N Carolina State Univ, Dept Phys, Raleigh, NC 27695 USA
[3] CSIRO Mat Sci & Engn, Clayton, Vic 3168, Australia
[4] Australian Synchrotron, Clayton, Vic 3169, Australia
[5] Monash Univ, Dept Mat Engn, Clayton, Vic 3800, Australia
基金
英国工程与自然科学研究理事会; 澳大利亚研究理事会;
关键词
POWER CONVERSION EFFICIENCY; OPEN-CIRCUIT VOLTAGE; DOMAIN PURITY; SIDE-CHAINS; RECOMBINATION; COPOLYMER; POLYMERS; SUBSTITUENTS; ENHANCEMENT; INTERFACES;
D O I
10.1021/jp501222w
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The device performance and microstructure of a series of PTB7-based polymers with varied molecular weight and degree of fluorination are investigated. Although the energy level of the highest occupied molecular orbital is found to increase with degree of fluorination, a strong relative molecular weight dependence of device performance dominates any underlying fluorination-dependent trend on overall performance. Microstructural investigation using a combination of X-ray techniques reveals a striking effect of polymer molecular characteristics on film morphology, with the size of PC71BM domains systematically decreasing with increasing polymer molecular weight. Furthermore, the relative purity of the mixed PTB7:PC71BM domain is found to systematically decrease with increasing molecular weight. When domain sizes with and without the use of the solvent additive diiodooctane (DIO) are compared, the effectiveness of DIO in reducing PC71BM domain sizes is also found to be strongly dependent on the molecular weight of the polymer. It is found that molecular weights of at least 150 kg mol(-1) are required for DIO to be effective in reducing the PC71BM domain size in order to produce high short-circuit current densities. Finally, it is shown that relatively high device efficiencies can be achieved with low degrees of fluorination; an efficiency of 4.6% is achieved for a degree of fluorination of only 5.3%.
引用
收藏
页码:9918 / 9929
页数:12
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