Abstract
Lead halide perovskite colloidal quantum dots (PQDs) are receiving great interest in emerging photovoltaics because of their excellent photovoltaic properties and the room-temperature processability without a thermal annealing step. Conductive thick PQD absorbers reported to date have been fabricated via multiple-step layer-by-layer deposition based on solid-state ligand exchange; however, this approach requiring a lot of processing time and cost is not suitable for the mass production. Thus, a single-step fabrication approach of conductive thick PQD absorbers should be devised. Herein, we demonstrate that conductive thick CsPbI3-PQD absorbers can be fabricated via a single-step process based on the surface ligand manipulation and employed in efficient PQD solar cells. We find that the conventional ethyl acetate-based post-treatment significantly removes long-chain ligands of the unexchanged PQDs (UN-PQDs) and cause film delamination of thick UN-PQD solids because of drastic volume shrinkage. Thus, we employ the methyl acetate-based post-treatment using phenethylammonium acetate (PEAOAc) to replace both long-chain oleate and oleylammonium within thick UN-PQD solids with short-chain PEA and OAc ligands without film delamination. To further reduce long-chain ligands within the resultant PQD solids, we also employ the PQDs prepared via a solution-phase ligand exchange (SPLE-PQDs) using the phenethylammonium iodide. Furthermore, we perform various spectroscopic measurements, including Fourier-transform infrared, nuclear magnetic resonance, and X-ray photoelectron spectroscopy, to quantitatively analyze the surface chemistry and ligands of PQDs. Consequently, CsPbI3-PQD solar cells, fabricated via a single-step process using SPLE-PQDs and PEAOAc post-treatment, show improved power conversion efficiency (13.7%) compared to that of the UN-PQD device (12.1%).
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