Charge transport in organic heterojunction transistors using small-molecule P-type-to-P-type semiconductors: An experimental and theoretical analysis

Abstract

A bi-channel hetero-transistor with an anti-ambipolar structure composed of two different n-type and p-type semiconductors is essential for manufacturing high-performance application devices such as multi-valued logics and neuromorphic devices. However, it is very difficult to understand the charge transport mechanism of antiambipolar hetero-transistor (AAHT), and many researchers are trying to understand the mechanism of AAHT. Nevertheless, it is difficult to find research results that clearly suggest the charge transport properties of AAHT. To understand the mechanism of AAHT fabricated by n-type and p-type, it is an easier approach to understanding the mechanism of organic heterojunction transistors fabricated by p-type and p-type. In this study, we investigate charge transport behavior in a heterojunction bi-channel composed of two small-molecule p-type-to-p-type semiconductors: dinaphtho[2,3-b:2 ',3 '-f]thieno[3,2-b]thiophene (DNTT) and 2,7-dioctyl[1]benzothieno[3,2-b] [1]benzothiophene (C8-BTBT). The hole mobility (mu hole) and threshold voltage (Vth) values extracted from the transfer curve for DNTT overlap bi-channel transistor (DOBCT) DNTT source operation was equal to 0.55 cm2V- 1s- 1 and -10.5 V, respectively, while those for C8-BTBT source operation were 0.58 cm2V- 1s- 1 and -31.4 V C8-BTBT overlap bi-channel transistor (COBCT) DNTT source operation was equal to 0.17 cm2V- 1s- 1 and -7.8 V, respectively, while those for C8-BTBT source operation were 0.21 cm2V- 1s- 1and -28.6 V. COBCT had a Vth close to zero compared to DOBCT, and it was confirmed that DOBCT had higher mobility than COBCT. The reason is related to the channel length. In the DOBCT, the DNTT channel area occupies a shorter length than the C8-BTBT channel area in the channel layer. Conversely, in COBCT, the DNTT channel area is longer than the C8-BTBT channel area. Therefore, DOBCT is dominantly influenced by the electrical characteristics of C8-BTBT, and COBCT is dominantly influenced by DNTT. Also, when the electrical characteristics of the source operating electrode were compared, the DNTT source was confirmed to improve Vth, and the C8-BTBT source was confirmed to improve mobility. The contact resistance between the C8-BTBT and the source electrode is 1.5 k omega cm. However, since DNTT has a small contact resistance of 1 k omega cm, Vth characteristics were improved due to enhanced charge injection when charges were injected through DNTT. Additionally, the temperature dependence and light-responsivity of DOBCT and COBCT were investigated, and the temperature dependence was affected by the channel length. In addition, due to the light-responsivity of DNTT, both DOBCT and COBCT reacted to light with a wavelength of 400 nm. For the reliability of the experimental results, finite element simulation was performed, and the agreement between the experimental results and the theoretical facts was demonstrated.