Title: Design of Cyanovinylene-Containing Polymer Acceptors with Large Dipole Moment Change forEfficient Charge Generation in High-Performance All-Polymer Solar Cells
Author: Han-Hee Cho, SeonhaKim, Taesu Kim, Vijaya Gopalan Sree, Sung-Ho Jin, Felix Sunjoo Kim, and BumjoonJ. Kim*
Journal: Advanced EnergyMaterials 2017, 8 (3), 1701436
Abstract: Designing polymersthat facilitate exciton dissociation and charge transport is critical for theproduction of highly efficient all-polymer solar cells (all-PSCs). Here, thedevelopment of a new class of high-performance naphthalenediimide (NDI)-basedpolymers with large dipole moment change (Δµge) anddelocalized lowest unoccupied molecular orbital (LUMO) as electron acceptorsfor all-PSCs is reported. A series of NDI-based copolymers incorporatingelectron-withdrawing cyanovinylene groups into the backbone (PNDITCVT-R) isdesigned and synthesized with 2-hexyldecyl (R = HD) and 2-octyldodecyl (R = OD)side chains. Density functional theory calculations reveal an enhancement in Δµge and delocalization of the LUMO upon the incorporation of cyanovinylenegroups. All-PSCs fabricated from these new NDI-based polymer acceptors exhibitoutstanding power conversion efficiencies (7.4%) and high fill factors (65%),which is attributed to efficient exciton dissociation, well-balanced chargetransport, and suppressed monomolecular recombination. Morphological studies bygrazing X-ray scattering and resonant soft X-ray scattering measurements showthe blend films containing polymer donor and PNDITCVT-R acceptors to exhibitfavorable face-on orientation and well-mixed morphology with small domainspacing (30–40 nm).