Time-Resolved Photoemission to Unveil Electronic Coupling between Absorbing and Transport Layers in a Quantum Dot-Based Solar Cell

Abstract

Lead sulfide (PbS) colloidal quantum dots-based photodiodes are remarkable structures obtained via colloidal engineering because of their outstanding optoelectronic performances. They combine surface ligand engineering to design a p-n junction with all solution processability. Here we investigate the PbS diode electronic structure combining static and dynamic photoemissions with transport measurements. We show that the n-type nature of the Icapped PbS CQDs shifts the valence band away from the Fermi level compared to the thiol capped nanocrystals. This change in majority carriers can be probed using time resolved X-ray photoemission spectroscopy (TRXPS). We also prove that the photo-induced binding energy shift depends on the nanoparticle surface chemistry. Finally, we demonstrate the ability of TRXPS to selectively probe the electronic structure of each side of an interface. We explore the PbS/MoO3 interface used as hole extractor in the PbS solar cell, using this method. We demonstrate that the PbS layer photosensitizes the MoO3 layer and that the two layers have a quasi-rigid electrostatic coupling. We identify the band bending occurring on the PbS(EDT)/MoO3 to be a limiting factor for the device performance and suggest strategies to overcome this limitation.

Coherent Spin Dynamics of Electrons and Holes in CsPbBr3 Colloidal Nanocrystals

“…From S e / S h ≈ 0.5, we suggest that the fractions of negatively and positively charged NCs are comparable, with some preference for the positively charged NCs. It was shown that in CsPbBr 3 and FAPbBr 3 NCs photocharging results in negative and positive loading of the NCs. , This is consistent with the Fermi level being close to the midpoint of the gap in Cs and FA lead halide NCs, as demonstrated by photoemission spectroscopy. , …”

“…35,36 This is consistent with the Fermi level being close to the midpoint of the gap in Cs and FA lead halide NCs, as demonstrated by photoemission spectroscopy. 37,38 The spin dephasing times, of both electrons and holes, show strong magnetic field dependences; see Figure 1f. The dynamics shorten from 0.6 to 0.05 ns for electrons and from 0.5 to 0.08 ns for holes with increasing field up to 1 T. This decrease is provided by the spin dephasing in the ensembles with a dispersion of the g-factors, which translates to a spread of the Larmor precession frequencies.…”

Mercury Chalcogenide Quantum Dots: Material Perspective for Device Integration

“…This method can be seen as a time-resolved transient photovoltage experiment that examines the surface band bending at the interface . This approach represents a powerful in situ method to probe the band alignment in optoelectronic devices. , Under dark conditions, a nonstoichiometric semiconductor presents surface band bending. Under illumination, electron–hole pairs are generated, and consequently, minority carriers flow toward the surface due to band bending.…”

Role of Cobalt Doping in CdS Quantum Dots for Potential Application in Thin Film Optoelectronic Devices

“…Co 2+ is a good activator of luminescence and provides good traps for the excited electrons which give the potential for optoelectronic devices. The increase of electron−hole generation gives the enhancement in the photocurrent which plays a very important role in optoelectronic devices like solar cell, 22 photodetectors, 23 OLET, 24 AC-electroluminescence, 25 etc.…”