Polymeric bulk heterojunction

In the following, we discuss strategies for optimizing the power efficiency of polymeric solar cells based upon bulk heterojunctions. 

The term heterojunction in semiconductors science refers to a connection of layers of material with different electric properties, such as band gaps. The term bulk heterojunction has been introduced in organic semiconductors, and refers to a polymeric composite that is microscopically phase separated, e.g., by an interpenetrating network. These materials are characterized by a high interfacial area. 

Vanderzande et al. reported the facile synthesis to 5,6-disubstituted-l,3-dithienylbenzo[c]thiophenes 3.10 via Pd°-catalyzed coupling reaction of 5,6-dichloroterthiophenes 3.9 with an alkyl Grignard reagent (Scheme 1.30) [309, 321]. Chemical polymerization of the 5,6-modified monomers with FcCIb yielded polymers with bandgaps of 1.4-1.8 eV, which are similar to that of poly(dithienylbenzo[c]thiophene) P3.3 [309]. Application of these polymers as donors and fullerene PCBM as acceptor in bulk heterojunction solar cells (BHJSC) was also investigated and reported. An overall power conversion efficiency of 0.3 % and an internal power conversion efficiency of 24% were obtained for PMMA-poly-P3.9c-PCBM (1 2 6) blended devices [321]. 

A systematic study of the effect of molecular weight on the photovoltaic performance has also been performed on poly(3-hexadecylthienylene vinylene) synthesized by ADMET polymerization [164]. The molecular weights of the polymers ranged from 6.0x10 to 3.0 X lO gmoD, and were incorporated into bulk heterojunction solar cells with [6,6]-phenyl-Cg -butyric acid methyl... 

C. H. Duan, C. M. Zhong, F. Huang and Y. Cao, Interface Engineering for High Performance Bulk-Heterojunction Polymeric Solar Cells, in Organic Solar Cells Materials and Device Physics, ed. W.C.H. Choy, Springer, 2013, pp. 43-79. 

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