A solution-processed nanoscale COF-like material towards optoelectronic applications

Two-dimensional (2D) covalent organic frameworks (COFs) with periodic functional n-electron systems are an emerging class of optoelectronic materials. However, almost all conjugated COFs so far are insoluble and hard to process, which hampers severely their optoelectronic applications. Here, a solution-processable, nanoscale and sp(2) carbon-conjugated COF-like material, PDPP-C20 was successfully designed and synthesized. The solution-processed PDPP-C20 films exhibit high crystallinity and excellent charge transport properties along out-of-plane directions, combined with the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of -5.36/-3.75 eV, making PDPP-C20 suitable for electronic device applications. An efficiency as high as 21.92% has been demonstrated when it was used as a functional interfacial layer in perovskite solar cells, coupled with dramatically improved stability in comparison with the control device due to the superior hydrophobicity of PDPP-C20 layer as well as its passivation effect on perovskite surface. Furthermore, the soluble PDPP-C20 could also be used as donor in bulk-heterojunction organic solar cells and an initial efficiency of 2.46% has been achieved. These results indicate that this new class of soluble and nanoscale COF-like materials should offer a new arena of functional materials for optoelectronic devices.