Overcoming Hole‐Extraction Barriers: A Facile PEDOT:PSS Interlayer Unlocks Record‐Low Voltage Deficit in PbS Quantum Dot Solar Cells

A synergistic methanol and oxalic acid interface engineering strategy is developed for PbS quantum dot solar cells. This approach transforms the PEDOT:PSS layer into a dense, electronically uniform, and conductive network. Consequently, the device achieves a record‐low voltage deficit of 340 mV, yielding a remarkable Voc of 742 mV and a power conversion efficiency of 13.97%. ABSTRACT The development of colloidal quantum dot solar cells (CQDSCs) is currently constrained by the substantial open‐circuit voltage (Voc) deficit and intricate fabrication processes. Here, we present a simplified device architecture achieved by synergistically combining a direct‐synthesis colloidal quantum dot (CQD) ink with a facile methanol/oxalic acid modification of the Poly(3,4‐ethylenedoxythiophene):polystyrene sulfonate (PEDOT:PSS) interlayer. This strategy simultaneously addresses the poor wettability of aqueous PEDOT:PSS on hydrophobic PbS‐EDT layers and initiates critical chemical optimization. By selectively removing insulating PSS, the treatment fosters a dense, electronically uniform fibrous network. Crucially, this optimized interlayer exhibits a work function shift from −5.30 to −5.15 eV, which reduces the hole extraction barrier to the Ag electrode from 0.51 to 0.36 eV. This favorable energy alignment extends the carrier lifetime from 0.54 to 2.37 ms and accelerates charge extraction. Consequently, the Voc is boosted from 649 to 742 mV, propelling the power conversion efficiency to 13.97%. This work offers a robust, process‐compatible interfacial strategy to unlock stable, high‐voltage CQDSCs. A synergistic methanol and oxalic acid interface engineering strategy is developed for PbS quantum dot solar cells. This approach transforms the PEDOT:PSS layer into a dense, electronically uniform, and conductive network. Consequently, the device achieves a record-low voltage deficit of 340 mV, yielding a remarkable V oc of 742 mV and a power conversion efficiency of 13.97%. ABSTRACT The development of colloidal quantum dot solar cells (CQDSCs) is currently constrained by the substantial open-circuit voltage ( V oc ) deficit and intricate fabrication processes. Here, we present a simplified device architecture achieved by synergistically combining a direct-synthesis colloidal quantum dot (CQD) ink with a facile methanol/oxalic acid modification of the Poly(3,4-ethylenedoxythiophene):polystyrene sulfonate (PEDOT:PSS) interlayer. This strategy simultaneously addresses the poor wettability of aqueous PEDOT:PSS on hydrophobic PbS-EDT layers and initiates critical chemical optimization. By selectively removing insulating PSS, the treatment fosters a dense, electronically uniform fibrous network. Crucially, this optimized interlayer exhibits a work function shift from −5.30 to −5.15 eV, which reduces the hole extraction barrier to the Ag electrode from 0.51 to 0.36 eV. This favorable energy alignment extends the carrier lifetime from 0.54 to 2.37 ms and accelerates charge extraction. Consequently, the V oc is boosted from 649 to 742 mV, propelling the power conversion efficiency to 13.97%. This work offers a robust, process-compatible interfacial strategy to unlock stable, high-voltage CQDSCs. Advanced Science, EarlyView.