The p–i–n quantum dot (QD) solar cells were fabricated through the single-step deposition of both of its p-type and light absorbing quantum layers. The hole transport and light absorbing layers of these devices were made by the p- and n-type PbS QDs, which were functionalized with mercaptopropionic acid and different halide, hybrid, and perovskite ligands, respectively. Fabrication of such p–i–n devices by the single-step deposition of pre-exchanged colloidal QDs had not been fully investigated so far because of the low progression of ligand exchange processes, weak colloidal stability of pre-exchanged QDs in desired solvents, and remaining of the ligand exchange products along with particles. However, we showed that the type of ligand complexes, amino acid products of ligand exchange, and protic solvents are highly effective for increasing the ligand exchange progression and preparation of high colloidal stability QDs with superior photoluminescence properties. As well, the surface chemistry investigations by the means of Fourier transform infrared, nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, inductively coupled plasma optical emission spectrometry, carbon–hydrogen–nitrogen–sulfur elemental analysis, zeta potential, and high-resolution transmission electron microscopy were led to the presentation of new concepts about the theoretical and experimental ligand weight percentages, the mechanisms of solution-phase ligand exchange processes, and formation of ligands adlayer on the (111) facets of QDs. The pre-exchanged colloidal QDs showed very good desirability for the single-step deposition of dense, defects-free, and smooth QD layers. Regarding that, the p–i–n solar cells were successfully fabricated by the single-step deposition of both of the QD layers. Especially, the highest power conversion efficiency value of 6.40% was recorded for the devices in which the light absorbing layer was prepared by the composite-like QD–perovskite structures.

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