In situ growth of perovskite single-crystal thin films (PeSCTFs) on the transport layer is crucial for achieving high-performance perovskite optoelectronic devices, such as solar cells, light emitting diodes, photodetectors, etc. However, in-situ growing PeSCTF on the transport layer with large-area, high-crystal-quality, and low-trap-density simultaneously remains challenging. This work proposes a method for in-situ growing large-area and low-trap-density MAPbBr₃ SCTFs on the PTAA transport layer with the assistance of cesium(I) bis(trifluoromethanesulfonyl)imide (CsTFSI) ionic liquid. After introducing the CsTFSI ionic liquid, the Cs⁺ ions enter the MAPbBr₃ lattice, reducing the formation energy, and the coordination between the lone pair electrons of O in TFSI^- and the empty orbital of Pb in MAPbBr₃ passivates the dangling bond defects of Pb, facilitating the formation of MAPbBr₃ SCTFs with high-crystal-quality. Moreover, the strong interaction between TFSI⁻ and the substrate can enhance wettability and reduce the contact angle, thereby promoting faster solute diffusion and enabling the growth of larger-area MAPbBr₃ SCTFs. Therefore, compared to the sample without CsTFSI addition, the MAPbBr₃ SCTFs with CsTFSI addition exhibit better thermal stability, larger area (increased from 1.79 to 19.68 mm², approximately a 10-fold increase), lower trap density (decreased from 6.86 × 10¹² to 5.39 × 10¹² cm⁻³), and higher carrier mobility (increased from 0.72 to 0.84 cm²∙V⁻¹∙s⁻¹). Moreover, the performance of the photodetector with CsTFSI, including responsivity, EQE, detectivity, and response speed, also increased significantly. This work provides an effective method for the in-situ growth of PeSCTFs with large-area, high-crystal-quality, and low-trap-density simultaneously on the transport layer.

Chiral perovskites (CPs) have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence (CPL) application and of great importance for future spin-optoelectronics. However, there is a key contradiction that in chiral perovskites chirality distorts the crystal structure, leading to poor photoluminescence (PL) properties. Achieving the balance between chirality and PL is a major challenge for strong CPL from chiral perovskites. Differently, two-dimensional (2D) chiral perovskite has shown fascinating chiral induced spin selectivity (CISS) effect which can act as spin injector under ambient conditions. Here, we propose an effective strategy to achieve high CPL activity generated from quantum dots (QDs) by introducing 2D chiral perovskite as a chiral source, providing spin polarized carriers through the CISS effect. The as-synthesized QDs/CP composites exhibit dissymmetry factors (g_lum) up to 9.06 × 10⁻³. For the first time, we performed grazing incident wide angle X-ray scattering (GIWAXS) measurements, showing the chirality originates from the distorted lattices caused by the large chiral organic cations. Besides, time-resolved PL (TR-PL) measurements verify the enhanced CPL activity should be attributed to the charge transport between two components. These findings provide a useful method to achieve CPL in QDs/2D chiral perovskite heterojunctions which could be promising in spin-optoelectronics application.