Mechanism of Organic Solar Cell Performance Degradation upon Thermal Annealing of MoO_x

Abstract

In this work we focus on P3HT:PC61BM bulk heterojunction (BHJ) devices with MoO3 at the hole extraction side of the BHJ, which relies on the formation of a strong dipole at the BHJ/MoO3 interface, as a reference system that has been extensively studied. We have observed, depending on when the annealing is performed during device fabrication, that the device performance either increased or decreased due to formation of a sharp or relatively diffuse interface, respectively, due to diffusion of MoO x into the BHJ. The measured strength of the dipole at this interface following thermal annealing correlated well with the width of the interface and device performance, with the sharper interface resulting in a stronger dipole and in improved device performance. This is expected to be a general phenomenon for evaporated coatings onto polymeric BHJ, regardless of the polymers involved.

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

“…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.…”

A History and Perspective of Non‐Fullerene Electron Acceptors for Organic Solar Cells

“…Moreover, also MoO x which has been shown to be more stable than PEDOT:PSS but may also cause significant degradation effects due to diffusion of MoO x into the active layer. [ 156 ] These findings stress the importance of the development of stable interface layers on the pathway toward stable solution processed organic solar cells.…”

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

“…The decrease in the MoO 3 work function indicates a decrease of the polarity of the surface of MoO 3 , this consequently decreases the dipole at the P3HT/MoO 3 interface, and therefore decreases the charge transport over the interface. 36 In that way, Mo 6+ reduction to Mo 5+ leads to fast V OC and FF decays of devices, resulting in fast device performance degradation.…”