Exciton many-body interactions and charge transfer in CsPbBr3/graphene derivatives

Charge separation and many-body interactions at the interface of the light-absorbing semiconductor and contact layer are of crucial importance to the photophysical properties and optoelectronic device performance. Here, we report the exciton many-body interactions and charge transfer dynamics at the interface of metal halide perovskite nanocrystals and graphene derivatives [graphene oxide (GO) and reduced GO (RGO)] using ultrafast transient absorption (TA) and time-resolved photoluminescence (PL) measurements. At the early timescales, the TA spectra of ${\mathrm{CsPbBr}}_{3}/\mathrm{GO}$ and ${\mathrm{CsPbBr}}_{3}/\mathrm{RGO}$ show an asymmetric derivative feature originating from the exciton many-body interactions. The band gap renormalization and binding energies of exciton and biexciton of ${\mathrm{CsPbBr}}_{3}$ nanocrystals are significantly reduced in ${\mathrm{CsPbBr}}_{3}/\mathrm{GO}$(RGO) due to the charge transfer and change in the dielectric environment, respectively. More specifically, the exciton (biexciton) binding energy of ${\mathrm{CsPbBr}}_{3}$ nanocrystals, originally $38\ifmmode\pm\else\textpm\fi{}2$ ($34\ifmmode\pm\else\textpm\fi{}1$) meV, decreases to $27\ifmmode\pm\else\textpm\fi{}1$ ($22\ifmmode\pm\else\textpm\fi{}1$) meV in ${\mathrm{CsPbBr}}_{3}/\mathrm{RGO}$ and $17\ifmmode\pm\else\textpm\fi{}1$ ($15\ifmmode\pm\else\textpm\fi{}1$) meV in ${\mathrm{CsPbBr}}_{3}/\mathrm{GO}$. Furthermore, we observe a reduction in the Auger recombination rate and exciton PL quenching in ${\mathrm{CsPbBr}}_{3}/\mathrm{GO}$ and ${\mathrm{CsPbBr}}_{3}/\mathrm{RGO}$, corroborating the charge transfer mechanism. Our systematic studies successfully describe photoexcited charge transfer from ${\mathrm{CsPbBr}}_{3}$ nanocrystals to GO (RGO) in $7.0\ifmmode\pm\else\textpm\fi{}0.4$ ($4.2\ifmmode\pm\else\textpm\fi{}0.1$) ps, which is one order of magnitude faster than the charge transfer for other acceptor materials such as metal oxide, fullerene, anthraquinone, 1-aminopyrene, and phenothiazine. Our results offer insights and guidance for perovskite-based high-performance optoelectronic devices.