Cross-Linking of Doped Organic Semiconductor Interlayers for Organic Solar Cells: Potential and Challenges

Solution-processable interlayers are important building blocks for the commercialization of organic electronic devices such as organic solar cells. Here, the potential of cross-linking to provide an insoluble, stable, and versatile charge transport layer based on soluble organic semiconductors is studied. For this purpose, a photoreactive tris-azide cross-linker is synthesized. The capability of the small molecular cross-linker is illustrated by applying it to a p-doped polymer used as a hole transport layer in organic solar cells. High cross-linking efficiency and excellent charge extraction properties of the cross-linked doped hole transport layer are demonstrated. However, at high doping levels in the interlayer, the solar cell efficiency is found to deteriorate. Based on charge extraction measurements and numerical device simulations, it is shown that this is due to diffusion of dopants into the active layer of the solar cell. Thus, in the development of future cross-linker materials, care must be taken to ensure that they immobilize not only the host but also the dopants.

Automated summary

This study explores the potential of cross-linking technology in organic electronic devices, particularly in organic solar cells. A newly synthesized photoreactive tris-azide cross-linker demonstrated high efficiency and excellent charge extraction properties in a p-doped polymer used as a hole transport layer. However, high doping levels in the interlayer were found to decrease solar cell efficiency due to dopant diffusion into the active layer. Care must be taken in future cross-linker material development to immobilize both the host and dopants effectively.