The latest research results of the team of Wu Yongzhen and Zhu Weihong of East China University of Science and Technology and their collaborators in the field of organic hole transport materials are reported online.

In this work, cyanophosphonic acid units are introduced, biparental small molecule hole transport materials are developed, and ordered, ultra-thin and surface ultra-infiltrated layers are constructed by dynamic self-assembly. "Killing two birds with one stone" perfectly solves the two major problems of carrier transport and interface defect control in device applications.

As an important class of organic semiconductor materials, organic hole transport materials have been widely used commercially in the fields of electrostatic copying, laser printing and organic light-emitting diodes,

and play an important role in new photovoltaic technologies such as dye-sensitized solar cells, organic photovoltaic cells and perovskite solar cells. However, organic hole transport materials still face many problems in the application of optoelectronic devices, the most prominent of which is that their low mobility characteristics limit the charge transport performance.

In response to this bottleneck problem, previous studies mainly improve the conductivity of thin films by introducing "chemical doping", but the process is complex, difficult to prepare, poor reproducibility,

and is not conducive to the long-term stability of the device. After long-term research accumulation and a lot of experimental exploration, the research team innovatively proposed the anchoring self-assembly strategy, which effectively solved the two major problems of carrier transport and interface defect control.

The main innovative achievements of this research include dynamic anchoring self-assembly, constructing ordered ultra-thin films to break through the bottleneck of hole transport; Biparental design to achieve surface superwetting and interface defect control;

A "double layer" film structure was constructed on a transparent conductive substrate indium tin oxide by dynamic anchoring self-assembly using biparental small molecule hole transport materials. Solve carrier transport and interface defect control problems, breaking the trans-perovskite solar cell certification efficiency record.

This work innovatively introduces cyanophosphonic acid units, develops biparental small molecule hole transport materials, and constructs ordered, ultra-thin, surface-wetting layers through dynamic self-assembly.

As an important class of organic semiconductor materials, organic hole transport materials have achieved large-scale commercial applications in the fields of electrostatic copying, laser printing and organic light-emitting diodes,

and also play an important role in new photovoltaic technologies (such as dye-sensitized solar cells, organic photovoltaic cells and perovskite solar cells), but there are still many problems in the application of optoelectronic devices.

The most prominent bottleneck problem is that its low mobility characteristics limit charge transport performance. Previously, the field mainly through the introduction of "chemical doping" to improve the conductivity of thin films, but the process is complex, difficult to prepare, poor reproducibility, and is not conducive to the long-term stability of the device.

The team innovatively proposed the anchoring self-assembly strategy, which effectively solved the two major problems of carrier transport and interface defect control. Key innovations include:

Dynamic anchoring self-assembly, the construction of ordered ultra-thin films to break through the bottleneck of hole transport. Professor Wu Yongzhen and Zhu Weihong proposed to construct a uniform, ordered and ultra-thin charge transport layer at the monolayer level by using the dynamic anchoring self-assembly strategy,

which greatly improved the hole transport efficiency. The feasibility of the device application of self-assembled ultra-thin films was verified in the previous work, and the universality of this strategy was confirmed by the systematic design of molecular connecting units and anchoring groups.

Biparental design to achieve surface superwetting and interface defect control. After comparing carboxylic acid, sulfonic acid, phosphonic acid, boric acid, cyanoacetic acid and other anchoring groups,

a new generation of cyanophosphonic acid anchoring organic hole transport material was designed. The introduction of strong electron-absorbing cyanogen group increases the deprotic ability of phosphonic acid and the hydrophilicity of the anchoring group,

making the small molecule material with unique amphiphilic characteristics, easily soluble in various solvents of different polarity. The ultra-wide window of optional solvents gives the material flexible processing methods and a wide range of application scenarios.

Using the biparental small molecule hole transport material, a "double-layer" film structure was constructed on a transparent conductive substrate indium tin oxide (ITO) by dynamic anchoring self-assembly,

namely "anchoring self-assembled ordered monolayer" and "unanchoring disordered overlay". The former can be firmly attached to the surface of ITO to ensure efficient hole selection and transport,

and the latter has super-wetting characteristics, which is not only conducive to the uniform preparation of the large area of the upper layer film, but also can effectively reduce the defect concentration of the interlayer interface.

Solve carrier transport and interface defects, breaking the trans-perovskite solar cell certification efficiency record. The new type of small molecule hole transport material has many advantages such as anchoring, easy dissolution,

easy processing and super-wetting. The trans-structure perovskite solar cell prepared based on this material achieved 25.39% certification efficiency in the third party, which is the highest certification efficiency of this kind of solar cell at present.