Hole Transfer Dynamics from Photoexcited Cesium Lead Halide Perovskite Nanocrystals: 1-Aminopyrene as Hole Acceptor

The lead halide perovskites have emerged as promising materials for photovoltaic applications within a very short period. The key to exploitation of the full potential of these substances by achieving even higher photovoltaic conversion efficiency lies in understanding of the charge (electron/hole) separation process and their transfer across the interface. As the latter depends on the nature of the electron/hole acceptor, quest for suitable carrier acceptor is an active area in this context. Herein, we explore the hole extraction ability of 1-ampinopyrene (AMP) from two very common all-inorganic perovskite nanocrystals (NCs), CsPbBr3 and CsPbI3, with different band gaps. The observation of efficient quenching of the photoluminescence (PL) of the NCs with little/negligible change in PL time profile in the presence of AMP indicates static interaction of the two interacting species. The band alignment of the NCs relative to the HOMO-LUMO energy levels of AMP and ultrafast pump-probe measurements reveal rapid hole transfer from the photoexcited NCs to AMP. The hole transfer time constants are estimated as 120 and 170 ps for CsPbBr3 and CsPbI3 NCs, respectively. The rapid extraction of the hole, as observed with the present system, appears to be the result of strong anchoring of AMP on the NCs surface and facile transfer of the hole through conducive pyrene framework. The findings reveal that judicial choice of even a simple molecular system like the present one can help rapid transfer of photogenerated carriers and contribute to the development of cost-effective solar cells in the future.