Developing High‐Performance Electron‐Rich Unit End‐Capped Wide Bandgap Oligomeric Donor by Weak Electron‐Deficient Central Core Strategy

• Published in: Solar RRL 2018-02, Vol.2 (2), p.n/a
• Main Authors: Wang, Jin‐Liang, Liu, Kai‐Kai, Liu, Sha, Xiao, Fei, Liu, Feng, Wu, Hong‐Bin, Cao, Yong
• Format: Article
• Language: English
• Subjects: difluorobenzotriazoles cored oligomers; fullerene‐based organic solar cells; hexafluorinated molecular design; two‐step annealing; weak electron‐deficient central core
• ISSN: 2367-198X; 2367-198X
• DOI: 10.1002/solr.201700212

Here, we report the synthesis of a pair of end‐capped hexafluorinated oligomeric donors with electron‐rich unit for fullerene‐based organic solar cells, named as BTZ6F and BTA6F, which include the same difluorobenzothiadiazoles as internal electron‐deficient unit, but differ in distinct electron‐deficient central core, respectively. BTA6F with difluorobenzotriazoles as weak electron‐deficient central core, shows slightly wider bandgap, higher hole mobility, more ordered and crystalline blend film, and better device performances in term of higher PCE, Jsc, and FF. Moreover, the PCEs and fill factors show damatically increase upon SVA or a combined TA and SVA treatment, which can be ascribed to an optimal morphology with highly crystalline content and clearly nanoscale phase separation as revealed by morphology characterization. As a result, the devices from BTA6F exhibit a PCE of 9.04%, which is the best organic solar cell based on difluorobenzotriazoles cored oligomers as a donor reported to date. Equally important, the obtained wide bandgap oligomer BTA6F is among one of the few electron‐rich unit end‐capped oligomeric donor that can deliver high PCE of 9%. These results highlight the weak difluorinated electron‐deficient central core strategy as a promising approach to further improve the photovoltaic performance of electron‐rich unit end‐capped oligomers. A pair of similar hexafluorinated substituted oligomers (BTZ6F and BTA6F) with distinct electron‐deficient central core (difluorobenzothiadiazoles and difluorobenzotriazoles) are synthesized for donor materials in organic solar cells. The best PCE of 9.04% is achieved for BTA6F:PC71BM blends with TA + SVA treatment, which is the highest value of fullerene‐based organic solar cells with difluorobenzotriazoles cored oligomers as a donor.