Dipole Formation at the MoO₃/Conjugated Polymer Interface

Abstract

MoO 3 is known as high work function (WF) transparent metal oxides. It is used as anode buffer layer in organic based solar cells because of its capability to extract electrons and inject holes from the active layer due to its high WF. Here a broad range of techniques is used to determine the energy levels of the bulk heterojunction (BHJ) and MoO 3 to determine that the minimum deposition thickness to achieve a closed layer is 1 nm due to penetration of the evaporated MoO 3 into the BHJ. The investigation shows that upon evaporation of the MoO 3 , a strong dipole is formed at the extended interface between the active layer and the MoO 3 and that the strength of the dipole increases with increasing thickness of the MoO 3 layer and saturates at 2.2 eV at a thickness around 3 nm.

High Efficiency Perovskite‐Silicon Tandem Solar Cells: Effect of Surface Coating versus Bulk Incorporation of 2D Perovskite

“…The notable reduction in the WF of the materials suggests that the surface‐coating layer greatly modified the electronic properties of the 3D perovskite surface, such as energy level structure. Since Fermi level aligns due to the equilibrium of electrons at the perovskite/HTL interface, we speculate that this reduction in the WF of perovskite caused more upward energy band bending at the interface due to the increasing difference between the WF , and that this along with the reduction in surface defects was responsible for the enhanced V OC and FF of the devices. In the bulk incorporated samples, the change in the WF was contrastingly different.…”

The Importance of Schottky Barrier Height in Plasmonically Enhanced Hot‐Electron Devices

“…The Fermi levels of individual components align at the interfaces of individual materials resulting in band bending. [ 34–37 ] The band bending at the interfaces could not be directly measured, as in the study by Yin et al., [ 34 ] because the height of the Au NPs is larger than 3 nm, meaning that the interface beneath the particles is out of the scope of UPS. Instead, the energy band bending at the interfaces can be estimated from the spectra in Figure 4, as reported in reference.…”

“…Instead, the energy band bending at the interfaces can be estimated from the spectra in Figure 4, as reported in reference. [ 34,38,39 ] Arshad et al. calculated the SBH at the interface between TiO 2 and Au by XPS analysis on the VBM; [ 16 ] however, Marri and Ossicini emphasized that the CBM should be used to determine the SBH at the metal/n‐type semiconductor interfaces.…”

“…The emitted electrons were detected with a Phoibos 100 electron energy analyzer from SPECS. The WF of a sample was determined by extrapolating the cutoff of secondary electron cascade [ 34,38 ] and valence band structure can be determined from the cutoff of high kinetic energy electron distribution of the acquired spectra.…”

The interfacial degradation mechanism of polymer:fullerene bis-adduct solar cells and their stability improvement

“…MoO 3 is used as the hole transport layer to boost the charge transport efficiency of polymer solar cells, which has been ascribed to the formation of dipoles at the active layer/MoO 3 interface, based on the alignment of the highest occupied molecular orbital (HOMO) of the organic layer and the conduction band of MoO 3 . 33 The position of aligned energy levels can be estimated from the work function. 34 In order to further understand the mechanism of device performance degradation caused by the reduction of MoO 3 , UPS spectra of P3HT:bis-PC 61 BM/MoO 3 films illuminated for different hours were tested, as shown in Fig.…”