Diode rectification and negative differential resistance of dipyrimidinyl–diphenyl molecular junctions

• Temperature- and light-dependent diode rectification and NDR are observed.
• Interfacial asymmetry and dipole effect result in distinct rectification efficiency.
• NDR behaviors depend largely on molecular S–Au contact geometry.
• NDR weakens with temperature increase due to enhanced molecular interactions.
• Barrier height depends highly on light irradiation, temperature and bias polarity.

Addressable Au/dipyrimidinyl–diphenyl/Au molecular junctions are fabricated using elastic polymer stamp-printing method. To study the charge transport, current–voltage measurements are carried out from 95 up to 295 K in vacuum under both dark and light conditions. Reversible diode rectification and negative differential resistance phenomena are observed. The rectification efficiency dramatically decreases upon temperature increase or light illumination. Theoretical calculations based on the non-equilibrium Green’s function method combined with the density functional theory is performed to elucidate the negative differential resistance behaviors. We show that the different rectification efficiency is caused by the interfacial asymmetry and the dipole effects. The negative differential resistance may be attributed to the variation of the coupling degree between the incident states of the Au electrodes and the molecular orbitals, which depends largely on the S–Au contact geometry. The direct tunneling and Fowler–Nordheim tunneling act as the main transport mechanisms for low and high bias regions, respectively. The barrier height depends largely on the light illumination, substrate temperature, and bias polarity. The distinctly different adsorbing nature of the Au/molecule interface may account for the performances.

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