Differential capacitive response of poly (3-hexylthiophene) diodes and effects of air exposure

• Published in: Synthetic metals Vol. 253; pp. 141 - 145
• Main Authors: da Cunha, Mariana Richelle P., Maciel, Alexandre C., Faria, Roberto M., da Cunha, Helder N.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-07-2019; Elsevier BV
• Subjects: Capacitance-voltage; Diodes; Doping; Exposure; p-doping; Poly(3-hexylthiophene); Thin films; Traps; Poly(3-hexylthiophene); Capacitance-voltage; Traps; p-doping
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/j.synthmet.2019.05.012

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•Differential capacitance in ITO/P3HT/Al diodes recorded by C−V measurements.•Electron traps and p-doping in P3HT thin-films caused by oxygen molecules.•Change in the P3HT´s Fermi level and of its alignment with the electrodes work functions due to the action of oxygen.
The origin of capacitance peaks in C–V measurements often observed in organic thin-film diodes is still waiting for a definitive explanation. It has been reported that one of two-peak C–V detected in p-doped material based devices are caused by involuntary doping, while the second one is attributed to trapped carriers. In this study, we show a ITO/P3HT/Al diode exhibiting one C–V peak at approximately 0.48 V, in both non-exposed and air-exposed devices. The second peak, (around 1.5 V) arises when the device is exposed to air, and increases significantly with exposure time. We suggest that the second peak is originated by a volumetric p-doping of P3HT due to the action of oxygen and the formation of electrons deep traps. A simple model to explain the C–V experiments is presented and is in agreement with this hypothesis.