High open-circuit voltage in lead sulfide quantum dot solar cells via solution-phase ligand exchange with low electron affinity cadmium halides

Abstract

The deployment of colloidal quantum dots (QDs) in building high-performance solar cells and other optoelectronic applications relies on the passivation of unsaturated surface atoms through ligand engineering to attain a...

Synthesis and Processing Strategy for High-Bandgap PbS Quantum Dots: A Promising Candidate for Harvesting High-Energy Photons in Solar Cells

“…To implement the high bandgap PbS QDs in solar cell building, a solution-phase ligand exchange strategy is developed to replace the insulating OA ligands with shorter ligands for efficient charge conduction in QD films. Recently, a hybrid ligand passivation strategy based on cadmium halides (CdI 2 and CdBr 2 ) and 3-chloro-1-propanethiol (CPT) 52 has been reported by our group for the solution-phase ligand exchange of PbS QDs, which led to the record open circuit voltage of 0.7 V in 1.28 eV bandgap QDs. We attempted to implement the same ligand combination for the solution phase ligand exchange of the ultrasmall diameter 1.61 eV bandgap QDs.…”

“…Solar cells with Spiro HTL show a lower η (1.20) compared to PbS-EDT (1.55), indicating a reduction in photocarrier recombination in Spiro HTL based solar cells. Further, we estimate the reverse saturation current density (J 0 ) of solar cells using the equation 52 ( )…”

“…We first determine the radiative limit of V oc ( V oc rad. ) from their respective EQE plots using the reported process , (Section 2; SI). The nonradiative voltage is determined using the equation (Δ V oc non.…”

“…From the light intensity dependent V oc , we determine the diode ideality factor for solar cells (Figure c) using the equation ( V oc = η K T q ln true( normalΦ true) ) Solar cells with Spiro HTL show a lower η (1.20) compared to PbS-EDT (1.55), indicating a reduction in photocarrier recombination in Spiro HTL based solar cells. Further, we estimate the reverse saturation current density ( J 0 ) of solar cells using the equation V oc = η K T q ln ( J normalsc J 0 ) . As shown in Figure d, the reverse saturation current density is 1.5 × 10 3 times lower in Spiro HTL-based solar cells (3.85 × 10 –11 mA/cm 2 ) compared to PbS-EDT HTL-based solar cells (2.48 × 10 –8 mA/cm 2 ).…”

“…For the deposition of the active QD layer, 52 the ZnO substrates were heated to 60 °C on a hot plate. They were then quickly moved to a spin coater where preprepared cadmium halide and propanethiol passivated PbS QDs were spin-coated at a rotation speed of 4000 rpm for 40 s to form the active layer.…”