Using an Atomically Thin Layer of Hexagonal Boron Nitride to Separate Bound Charge-Transfer Excitons at Organic Interfaces

Abstract

We successfully use two-dimensional hexagonal boron nitride (h-BN) as a continuous and ultrathin insulator to facilitate the conversion of excitons into free carriers at organic donor-acceptor (D-A) interfaces. Monolayer- (0.33 nm) thick h-BN with a lateral size on the order of 1 cm2 is inserted between zinc phthalocyanine (ZnPc) and perylenetetracarboxylic diimide (PTCDI) organic films that form a generic D-A interface. We find that h-BN increases the photon-to-free-carrier conversion yield of the D-A heterostructure by 130% compared with identical samples without a h-BN layer, even though h-BN lowers the initial electron-transfer rate from ZnPc to PTCDI. The enhanced photon-to-free-carrier conversion yield is attributed to a larger charge-separation yield of charge-transfer (CT) excitons at the D-A interface. h-BN can prohibit the formation of tightly bound CT excitons and impede electron-hole recombination, which can improve the charge-separation yield.