Thermal degradation of p-doped organic homojunction

Abstract

The stability of doped organic semiconductors is one of the essential features to achieve stable and high-performance organic optoelectronic devices with low power consumption. In this study, the thermal degradation of an organic homojunction, consisting of an intrinsic organic layer and a molybdenum oxide (MoO3)-doped organic layer, is investigated by impedance spectroscopy (IS) under thermal heating. The IS analysis indicates that the thermal deformation of the intrinsic organic layer is more significant than that of the underlying doped organic layer. A charge-transfer complex absorption peak analysis by ultraviolet-visible spectroscopy confirms that the thermal degradation is related to the deformation of organic host molecules rather than to diffusion of dopants. These results show that the organic homojunction is degraded owing to the crystallization of intrinsic organic molecules at high temperatures, above the glass transition temperature (Tg), rather than because of disruption of the interface at the homojunction by dopant diffusion. This study shows that hole-transport molecules having high Tg should be selected to provide stable electronic devices with organic homojunctions, thus paving the way for the development of novel devices with higher performance.

Intrinsic Organic Semiconductors as Hole Transport Layers in p–i–n Perovskite Solar Cells

“…The thermal instability of solar cells, including small‐molecule HTLs, might originate from other phenomena, for example, temperature‐induced aggregation, [ 66 ] which has been shown to readily occur in TcTa and NPB thin films at elevated temperatures. [ 67 ] To test this hypothesis, we have studied the surface properties of thin TaTm films before and after annealing at 85 °C for several hours. X‐ray photoemission spectroscopy of as‐prepared and thermally stressed films reveals that no chemical changes (i.e., oxidation) occur during annealing of this small molecule (Figure S12, Supporting Information).…”