Synergetic passivation of PbS colloidal quantum dots by bulk heterojunction-type interlayers enables >14% solar cell efficiency

Abstract

PbS colloidal quantum dots (CQDs) are promising low-bandgap absorbers for solutionprocessable photovoltaics, yet their performance is restricted by surface traps that induce nonradiative recombination and suppress the open-circuit voltage (VOC) and fill factor (FF).Conventional ligand treatments only partially reduce trap density, leaving residual defects at buried interfaces. Herein, we report an interfacial engineering strategy using two near-infrared non-fullerene acceptors (NFAs), BTPV-4F and BATPV-4F, incorporated as bulk heterojunction-type hole-transporting layers (BHJ-HTLs) on PbS CQDs. These NFAs possess deep HOMO levels, strong quadrupole moments, and ordered π-π stacking, which enable selective hole extraction and suppress trap-assisted recombination rather than serving as additional light harvesters. The ternary BHJ-HTLs engage in multi-site coordination with PbS surfaces through Pb-S, Pb-F, and Pb-O interactions, while improving molecular ordering and preserving favorable band-edge alignment. Such synergistic interactions suppress interfacial trap states, enhancing carrier extraction and stability. Despite their broad absorption to ~950 nm, they yield only a modest photocurrent increase. Instead, simultaneous improvements in VOC (0.65 to 0.68 V) and FF (68.1% to 70.94%) dominate efficiency gains, boosting solar efficiencies from 11.99% to 14.02%. This work demonstrates a molecular design strategy that advances efficiency and durability in low-bandgap CQD photovoltaics.