Photoinduced electron-transfer from all-inorganic CsPbBr3 perovskite nanocrystals to naphthalenediimides

Electron-acceptor organic molecules have been shown recently to quench the photoluminescence (PL) of CsPbBr3 perovskite nanocrystals (NC). The phenomenon has been attributed to electron-transfer from the CsPbBr3 NC to the surface-bound acceptor. Here we exploit the use of naphthalenediimides (NDI) as electron-acceptors for CsPbBr3 NC. For this purpose, we employed N,N′-bis(3-triethoxysilylpropyl)-1,4,5,8-naphthalenediimide (SNDI), a NDI derivative bearing silane groups, which was synthesized by our group. Addition of SNDI to a toluene solution of CsPbBr3 NC resulted in blue-shifts in both absorbance and PL maxima, concomitant with PL quenching, suggesting binding of SNDI to the surface of the NC. Time resolved PL experiments did not show a faster decay upon addition of SNDI to the CsPbBr3 NC, indicating the static nature of the quenching. Complex formation between SNDI and CsPbBr3 NC was further studied by infrared spectroscopy. Electrochemical measurements, along with the optical data, allowed the construction of an energy level diagram, which shows that the conduction band of the perovskite lies higher in energy than the LUMO of SNDI, making electron transfer a thermodynamically favorable process. These results place SNDI as a suitable candidate for ETL in perovskite based solar cells.