their attention to the cesium-based inorganic perovskite of CsPbX 3 (X = Cl, Br, and I), which possess favorable thermal endurance, and component stability. [12] Among these CsPbX 3 , the representative CsPbI 3 light-absorbing material has become a research hotspot for its suitable band gap (E g ) and high absorption coefficient. [13] However, the relatively high defect density and nonradiative recombination are still primarily obstacles to improve CsPbI 3 PSCs performance. [14] Meanwhile, surface and interfacial defects on film can create ion migration channels to accelerate degradation of CsPbI 3 PSCs. [15] Therefore, reducing its defect density, suppressing nonradiative recombination, and enhancing stability are of great significance to improve the device performance.Previous studies have shown that energy band mismatch produces nonradiative recombination at perovskite film/transport layer interface. [16] Meanwhile, there are also many defects on film surface, especially at grain boundaries (GBs), which can cause charge recombination. [17] All of this causes a lot of energy loss. Interface engineering is an efficient and reliable strategy, which mainly through interface modification, adding buffer layers, dopant and so on to optimize interfacial contact and film morphology. [18][19][20] Appropriate interface engineering not only can achieve energy level alignment, but also passivate surface defects, which greatly improves the PCE of PSCs. [21,22] For instance, Xu et al. introduced the (CsPbI 2 Br) 1−x (CsPbI 3 ) x layer as intercalation layer between CsPbI 2 Br film and hole transport layer (HTL) to minimize the energy loss, resulting in good crystalline quality and energy level alignment. [23] Tian and co-workers employed cathode interlayer and anode interlayer to tune the work function of SnO 2 and improve the crystallinity of CsPbI 2 Br film with larger grain size. The interaction of these interlayers can also passivate surface trap states of CsPbI 2 Br film. [24] These works directly demonstrate the feasibility of interface engineering.Currently, inorganic perovskite colloidal quantum dots (QDs) are widely used in interface engineering due to their unique features such as tunable energy levels, low excitation energies, excellent ambient stability and so on. [25][26][27] These merits show huge application prospects as interface modifiers. [28] According to previous reports, incorporation of QDs can passivate defects and tune surface morphology of perovskite film, thus retarding carrier recombination. [29][30][31] Through the insertion of QDs layer, CsPbI 3 has drawn constant interest in the field of perovskite solar cells (PSCs), due to its remarkable photovoltaic performance and thermal stability. Nonetheless, further development of CsPbI 3 PSCs requires solving larger energy loss problem, which is primarily caused by charge recombination and energy band mismatch at the interface. Here, a double-layer interface engineering concept is introduced that uses CsPbBr 3 and CsPbCl 3 colloidal quantum dots (QDs) t...