The effect of TiO₂ surface on the electron injection efficiency in PbS quantum dot solar cells: a first-principles study

Abstract

We present a density functional theory (DFT) study aimed at understanding the injection and recombination processes that occur at the interface between PbS QDs and TiO2 oxide nanoparticles with different morphologies. The calculated injection rates fall in the picosecond timescale in good agreement with the experiments. In addition, our simulations show that the (101) facet of TiO2 more favourably accommodates the QD, resulting in stronger electronic couplings and faster electron injections than the (001) surfaces. Despite this, the (101) slab is also more prone to faster electron recombination with the valence band of the QD, which can lead to overall lower injection efficiencies than the (001) surface.

First-Principles Study of the Electron–Hole Recombination Rate at the Interface of the CdSe Quantum Dot and TiO2 Substrate

“…In fact, the defect mechanism has been used to interpret the fast recombination rates in DSSCs, which would otherwise be unaccountable. The situation is even more so for QD sensitizers because they also develop localized states on their surface, which could act as traps for the photogenerated holes …”

“…51 For the studied six QDs, the gaps decrease with the size except for N = 6, implying wider absorbing windows for larger structures, which is in agreement with the previous studies. 16,26 It is normal that (CdSe) 6 does not follow the trend. Oscillations often occur for the small-sized systems in their geometrical and electronic structures.…”

“…The lowest energy structures are used in subsequent calculations. The stoichiometric anatase TiO 2 (101) surface is cleaved from bulk TiO 2 as a periodic slab due to its thermodynamic stability for the (101) facet. , This slab has a stepped structure with exposed 2-fold coordinated O atoms. A vacuum region 2.5 nm wide is added between the slab and its periodic image along the z direction.…”

“…The situation is even more so for QD sensitizers because they also develop localized states on their surface, which could act as traps for the photogenerated holes. 26…”

Effect of Adsorption Structure upon Directional Charge Transfer and Electronic Coupling in a Hybrid Dye Sensitizer based on a Cadmium Sulfide Quantum Dot

“…Those wave functions (diabatic states) corresponding to charge‐localized states were solved self‐consistently based on the CDFT potential, that is, the usual KS potential with the additional constraining potential. Here, we assumed charge transfer occurred at room temperature such that the electrons and holes were thermally relaxed to the band edge, [ 45,46 ] and, thus, hot carrier injection from high‐lying donor states is not within the scope of this work. In our calculations, we considered three scenarios, as illustrated in Figure 1 .…”