Unusual particle-size-induced promoter-to-poison transition of ZrN in counter electrodes for dye-sensitized solar cells

It is well-known that promoter and poison are two contradictory properties of materials. However, in this work, an unusual particle-size-induced promoter-to-poison transition of ZrN has been observed for the counter electrode of poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS) in dye-sensitized solar cells (DSSCs). If the primary crystal particle size of ZrN is 37 nm, it plays a promoting role for PEDOT:PSS counter electrodes, leading to a remarkable increase in DSSC power conversion efficiency. In contrast, when its primary crystal particle size is decreased to 21 nm, ZrN becomes a serious poison for PEDOT:PSS counter electrodes. This finding would be important for the development of highly efficient DSSC counter electrodes.