In-situ surface patch-passivation via phosphorus oxygen bond for efficient PbS colloidal quantum dot infrared solar cells

PbS colloidal quantum dots (CQDs) have been widely applied in infrared (IR) solar cells, as they can broaden the photon conversion region beyond 1100 nm, which can help promote an extra 6% of power conversion efficiency (PCE) as bottom subcells for silicon solar cell. Although halide liquid exchange is the dominant passivation strategy for CQDs, it is difficult to passivate all the surface defects, especially for IR CQD, which leaves the main limitation for improving PCE. Here, a facile in-situ solution-processed patch-passivation strategy was first proposed for developing efficient PbS CQD IR solar cells. A typical Lewis base triphenylphosphine oxide (TPPO) was added to I−/Br− capped PbS CQDs, aiming at passivation with uncoordinated Pb2+ as a “patch-ligand”. As a result, the phosphorus oxygen bond coordination could help suppress the non-radiative recombination in CQD films. The TPPO-passivated devices delivered an IR PCE as high as 1.36% under silicon-filtered AM 1.5G, along with a promising open-circuit voltage (VOC) of 0.44 V, both of which are the highest among other single-junction solar cells with a band gap of ∼0.95 eV. The significant VOC and fill factor (FF) enhancement can be attributed to the decrease in defect density and faster charge transport in TPPO-passivated devices.