Organic Ligand Complementary Passivation to Colloidal-Quantum-Dot Surface Enables Efficient Infrared Solar Cells

Lead sulfide colloidal quantum dot (PbS CQD) solar cells present great potential in infrared (IR) conversion due to high IR absorption coefficient and solution processability. The large-size IR QDs introduce specific nonpolar (100) facets that undisplay in small-size CQDs. The neutrality of (100) facets and reversible ligand exchange process are crucial challenges for IR QD surface passivation. Here, organic halide salt phenethylammonium iodide/bromine (PEAX, X = I/Br) additive ligands are adopted to cooperate with traditional lead halides for QD surface passivation especially for (100) neutral facets. Both nuclear magnetic resonance (NMR) and density functional theory (DFT) simulation reveal that the organic ligand PEAX can bind on PbS QD planes to enhance passivation without compromising transport property. Further device related photophysical studies confirm the suppressed bulk and interface defect concentration. The optimal PEABr based solar cells possess a power con-version efficiency (PCE) of 12.28 % under solar AM1.5G (certified value of 11.98 %). The crystalline Si filtered efficiency reaches 1.42 %. Both efficiencies are the record values for such absorption range QD (excitonic peak similar to 1.3 mu m) solar cells. Moreover, the supplementary PEAX ligand suppress the migration of halogen ions and elevate device stability.