Imide-Functionalized Naphthadithiophene Containing Donor-Accepter Polymers for Solar Cell Applications

摘要

Bulk heterojunction (BHJ) solar cells based on conjugated polymers as donor materials and fullerene derivatives as acceptors have attracted tremendous attention in the research and have remained as one of the most promising systems for polymer solar cells (PSC). Potential advantages of polymer solar cells over conventional inorganic counterparts include low fabrication cost, light weight, substrate flexibility, facile structural and property modification, etc.1-3 To achieve high power conversion efficiencies (PCE), an ideal donor polymer should exhibit certain properties such as a narrow bandgap with broad absorption, high absorption coefficient, high hole mobility, appropriate molecular energy levels, nano-sized bicontinuous morphology, excellent stability and good solubility.4-6 One effective strategy to realize low bandgap polymers is to prepare donor-acceptor (D-A) copolymer containing alternating electron rich and electron deficient building blocks.7 Among various conjugated polymers, those containing polycyclic aromatic hydrocarbon (PAH) units have been widely explored for solar cell applications and some of them have shown promising performances.8 The forced planarity of fused PAH rings not only increases the π-electron delocalization, which lowers the bandgap, but also increases the possibility of interchain π-π stacking, which may improve the charge mobility.9 We have previously reported conjugated dendrimers and polymers based on PAH units.10-14 In this contribution, we report the synthesis of new D-A conjugated polymers which contain an imide-functionalized naphthadithiophene (INDT) as the acceptor and a 3,3’-dialkoxy-2,2’-bithiophene as the donor. Simple single-layer devices based on these polymers showed impressive power conversion efficiencies of up to 6.56%.