To determine the interaction between QDs and 5AVAI ligands, the ligands on the surface of QDs were characterized. As shown in
Fig. 3a, the signal peak at 1639 cm
−1 represents the N-H bending vibration of the amine functional group [
30], and the peak at 1571 cm
−1 is due to the asymmetric stretching vibration peak of carboxylate (COO
−) [
31], which indicates that there are OA, OAm or 5AVAI ligands on QDs surface. After 5AVAI ligand treatment, the peak of the C-N stretching vibration signal at 907 cm
−1 is enhanced [
32,
33], indicating that the ligand containing amino functional groups on the QDs surface was increased due to the combination of 5AVAI ligand and QDs. In addition, the high-resolution XPS spectrum (Fig. S4) shows that the binding energy of Pb 4
f in CsPbI
3 QDs treated with 5AVAI is significantly increased compared with the QDs without 5AVAI treatment. This shows that 5AVAI has a strong interaction with uncoordinated lead atoms on the surface of QDs, which makes the chemical environment of QDs change significantly. TGA showed that the weight of CsPbI
3 QDs with 5AVAI decreased by 32% at 500 °C, while the weight of CsPbI
3 QDs without 5AVAI decreased by 34%, indicating the decrease of long-chain ligands (
Fig. 3b). XRD patterns (
Fig. 3c) confirmed that the crystal structure of QDs did not change after treatment with 5AVAI ligands, all were the same cubic crystal structure. Time-resolved PL decay spectrum (
Fig. 3d) shows that the average fluorescence lifetimes of CsPbI
3 QDs with and without 5VAI are 7.1 and 5.5 ns, respectively, which proves that the defects of CsPbI
3 QDs can be effectively reduced by 5VAI ligand treatment, leading to enhanced radiation recombination. AFM was used to characterize the surface morphology of CsPbI
3 QDs films with and without 5AVAI treatment (Fig. S5). The root mean square (RMS) roughness of CsPbI
3 QDs film with 5AVAI is 3.25 nm, while that of CsPbI
3 QDs film without 5AVAI is 5.73 nm. This is attributed to the exchange of some long-chain OA and OAm ligands between 5AVAI ligands, and the closer accumulation of QDs reduces the surface roughness of the films. This ensures good contact between the CsPbI
3 QDs layer and the hole transport layer.