## 1 Introduction  
Perovskite solar cells (PSCs) have made significant achievements in the certified power conversion efficiency (PCE), which increases from 3.8% to 25.2% [1] in recent several years. In particular, organolead halide (e.g., MAPbI\({}_{3}\), MA = CH\({}_{3}\)NH\({}_{3}\); FAPbI\({}_{3}\), FA = CH(NH\({}_{2}\))\({}_{2}\)) perovskite photovoltaic (PV) devices attract extensive investigation owing to the remarkable benefits of their large absorption coefficient [2], outstanding charge carrier mobility and long carrier diffusion lengths [3; 4; 5; 6]. With the aim of designing higher-performance PSCs, it is critical to better understand the charge transfer (CT) from perovskite to charge transport layer. However, CT time scales in MAPbI\({}_{3}\) PSCs reported to date vary from sub-picosecond [7; 8; 9] to hundreds of picoseconds [3; 10; 11; 12] or nanoseconds [8; 13; 14], even for the same acceptor. For instance, [PERSON] et al. reported the charge-carrier transfer time of 0.40 ns and efficiency of 92% for MAPbI\({}_{3}\) with selective electron layers ([6,6]-phenyl-C61-butyric acid methyl ester, PCBM) [3]. [PERSON] et al. revealed the electron transfer time from MAPbI\({}_{3}\) to planar TiO\({}_{2}\) to be \(39.9\pm 2.5\) ps [10]. [PERSON] et al. estimated the electron injection rate from MAPbI\({}_{3}\) perovskite to TiO\({}_{2}\) to be \(11\pm 1\) ns [14]. One of the main reasons for huge differences in measured CT time in MAPbI\({}_{3}\) PSCs may arise from the material variations of the MAPbI\({}_{3}\) perovskite films. To fabricate MAPbI\({}_{3}\) films with the proper phase structure and crystalline orientation, essential for the light-electrical conversion, it is required sophisticated high temperature annealing and several other treatments [15; 16]. Therefore, the uniformity of the film crystallinity and the material composition can be hardly ensured. Compared with MAPbI\({}_{3}\), FAPbI\({}_{3}\) is superior in light absorption characteristics [17; 18; 19; 20; 21] and thermal stability [21; 22]. In particular, FAPbI\({}_{3}\) can be fabricated as quantum dots (QDs) which possess proper phase structure and crystalline orientation without the need of high temperature annealing [23; 24; 25]. Relative to bulk or thin-film perovskite materials, perovskite QDs (PQDs) possess high crystallinity during synthesis and exhibit unique features such as tunable bandgaps [26; 27] and high quantum yield [28; 29; 30; 31], which contribute to PV applications. The corresponding PSCs made of FAPbI\({}_{3}\) PQDs have been demonstrated to exhibit reasonable high PCEs [25; 32]. However, the investigation of CT processes to reveal the intrinsic transfer time and efficiency is still lacking, which hinders the clarification of the important factors limiting the PCEs. Unlike the exciton or charge diffusion in the MAPbI\({}_{3}\) thin films as the active layer of PSCs, the diffusion process in the active layer of FAPbI\({}_{3}\) PQDs critically relies on the electronic couplings between the PQDs before the free carriers are injected into the charge transport layer. Moreover, the charge injection processes strongly depend on the interfacial interaction between the PQDs and charge transport layers. It is unclear whether the electronic couplings between PQDs and at the interface of PQDs and charge transport layers are strong enough to ensure quick transport of the carriers to reach the interface within short time and yield effective charge injection before they are recombined within the PQDs. Herein, in order to clarify the CT process in planar junctions, we studied for the first time the dynamics of interfacial CT from FAPbI\({}_{3}\) PQDs to electron and hole transport layers (ETL and HTL) (tris(pentafluorophenyl)borane-doped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) HTL and TiO\({}_{2}\) ETL) by utilizing the ultrafast transient absorption spectroscopy (TAs).