Asymmetric B←N Embedded Molecules: A New Pathway toward Efficient Cathode Interlayers for Organic Solar Cells

Developing novel and efficient cathode interlayers (CILs) for organic solar cells has been a hot topic due to its significance to the device performance. In this work, a series of asymmetric molecules containing boron-nitrogen coordination bonds (B←N) with backbone dipoles is disclosed and innovatively applied as the CILs of OSCs. By tailoring the substituents on the boron, the dipole moments, intramolecular charge transfer (ICT) properties, and compatibility with active layer of these asymmetric B←N embedded molecules can be well manipulated. Interestingly, the interfacial dipoles can be successfully aroused by sandwiching these molecules in between the active layer and silver (Ag) cathode as the CILs and the work function of Ag can be readily reduced. In contrast to the CIL-free devices with moderate efficiency of 11.32%, the B←N modified devices exhibit a significantly improved efficiency of 17.06%, which are comparable to the performance of benchmark CIL of PDINO (17.04%), an amino N-oxide functionalized perylene diimide. This is the first report on the B←N embedded molecules with adjustable backbone dipoles for the cathode modifiers of OSCs, opening a new pathway toward efficient CILs.