The chemical structure of polymer/macromolecular semiconductor materials is generally dominated by a longer conjugated main chain, and the introduction of different chemical groups into the main chain or changing the main chain structure can modify the properties of the semiconductor. Conjugated long chains and diverse functional groups endow polymer/macromolecular semiconductor materials with high electron delocalization and charge transport capabilities. In the field of electron transport, acceptor refers to a group capable of accepting electrons. The introduction of acceptors into polymer/macromolecular semiconductors can effectively improve the electron transport ability, modify its optoelectronic properties, and obtain high-efficiency, low-driving voltage semiconductor devices. Common acceptors include diketopyrrolopyrrole, isoindigo, naphthalimide, benzothiadiazole and other imides.
Figure 1. Chemical structures of some acceptors
- N-type semiconductor materials: Ideal N-type semiconductor materials generally have lower LUMO (Lowest Unoccupied Molecular Orbital) energy levels. On the one hand, it is conducive to electron injection into the semiconductor layer. On the other hand, it can stabilize negative ions, making the material more stable in the air. The acceptor has an electron-withdrawing effect. The introduction of acceptors into the polymer/macromolecular structure enables the preparation of stable N-type semiconductor materials with strong electron transport capabilities. Commonly used acceptor groups are halogen atoms, cyano groups, carbonyl groups and imide groups. N-type semiconductors with excellent performance can increase the stability and efficiency of electronic devices, such as organic field effect transistors, organic photovoltaic cells, organic light-emitting diodes and other electronic devices.
- Bipolar semiconductor materials: By introducing acceptors into the polymer/macromolecular semiconductor building blocks, ambipolar semiconductor materials with high electron mobility and good stability can be obtained. Acceptor dimerization (two adjacent acceptor groups on the backbone) is a new strategy for modifying ambipolar semiconductor materials. This strategy has the following unique advantages: (1) receptor dimerization does not add new steric hindrance; (2) The dimerization of the receptor can reduce the HOMO (Highest Occupied Molecular Orbital) and LUMO energy levels of the polymer at the same time and increase the stability of the material; (3) The dimerized receptor can be obtained by self-coupling reaction, and the preparation is simple. Such semiconductor materials can enable electronic devices to obtain excellent bipolar transport properties, balance electron and hole transport forces, and stabilize device functions.
- Yingfeng Wang,Zhenglong Yan,Mohammad Afsar Uddin,Xin Zhou,Kun Yang,Yumin Tang,Bin Liu,Yongqiang Shi,Huiliang Sun,Aiying Deng,Junfeng Dai,Han Young Woo,Xugang Guo. Triimide-Functionalized n-Type Polymer Semiconductors Enabling All-Polymer Solar Cells with Power Conversion Efficiencies Approaching 9% [J]. Solar RRL, 2019, 3, 1900107.