Analysis of Knee Voltage for Organic Diode Fabricated from Sakon Nakhon Indigo

Indigo plantations are widespread across Sakon Nakhon province, Thailand. The pigment extracted from the indigo plant has the characteristic of being semiconductor. In order to effectively utilize the indigo pigments in the electronic applications, some essential properties of the materials need to be comprehensively investigated. In this study, indigo pigments were produced from fermentation and extraction processes from indigo leaves. The obtained indigo pigments were used to fabricate a back-to-back diode, and the measurement of the electrical properties, including voltage and current, resistance, and conductivity have been experimentally investigated. The analytical results showed that the voltage and current characteristics of the indigo pigment exhibited a high knee voltage at 1.5 V of the forward bias while the reverse bias saturation current also exhibited a high value, which was 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> A at reverse bias. The unbalanced waveform was reached because of the surface junction between indigo pigment and different electrode materials with work functions. From resistance and conductivity profiles, the 2<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> period shows the broadest range of high electrical potential bias because of the influence of R<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Indigo</inf> <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pigment</inf>, leading to the high knee voltage. Hence, indigo pigment tends to be developed as an organic semiconductor material for high electrical potential bias in commercial electrical devices.