Network-Stabilized Bulk Heterojunction Organic Photovoltaics

Bulk heterojunction organic photovoltaic (OPV) devices are multilayer organic devices that can be fabricated using low-cost and scalable solution processing methods, but current devices exhibit poor mechanical stability and degrade under deformation due to cracking and delamination. Recent approaches to improve mechanical durability involve modifying the side-chain or main-chain structures of conjugated polymers in the active layer, but in general it is difficult to simultaneously optimize electronic properties, morphology, and mechanical stability. Here, we present a general approach to improve the mechanical stability of bulk heterojunction active layers through incorporation of an internal elastic network. Network-stabilized bulk heterojunction OPVs are prepared using reactive small molecular additives that are rapidly cross-linked through thiol-ene coupling after processing the active layer. Thiol-ene reactions catalyzed by a base or initiated through short exposure to UV light produce insoluble, elastic thiol-ene networks in the active layer. We show through a combination of crack onset strain measurements, morphological analysis, and OPV device testing that network-stabilized OPVs with up to 20% thiol-ene network exhibit improved deformability with no loss in PCE, and we implement network stabilized bulk heterojunction OPVs to produce stretchable photovoltaic devices. This work represents a simple approach for improving the mechanical durability of bulk heterojunction OPVs.