Conjugated polymers containing Ba←N unit as electron acceptors for all-polymer solar cells

Polymer electron acceptors are the key materials in all-polymer solar cells (all-PSCs). In this review, we focused on introducing the principle of boron-nitrogen coordination bond (Ba <- N), and summarizing our recent research on polymer electron acceptors containing Ba <- N unit for efficient all-PSC devices. Two approaches have been reported to design polymer electron acceptors using Ba <- N unit. The one is to replace a C-C unit by a Ba <- N unit in conjugated polymers to transform a polymer electron donor to a polymer electron acceptor. The other approach is to construct novel electron-deficient building block based on Ba <- N unit for polymer electron acceptors. The polymer electron acceptors containing Ba <- N unit showed tunable lowest unoccupied molecular orbital (LUMO) energy levels and exhibited excellent all-PSC device performance with power conversion efficiency of exceeding 6%. These results indicate that organic boron chemistry is a new toolbox to develop functional polymer materials for optoelectronic device applications.