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

TL;DR

This study explores cross-linking of doped organic semiconductor interlayers to improve stability and charge transport in organic solar cells, highlighting potential benefits and challenges such as dopant diffusion affecting efficiency.

Contribution

It introduces a photo-reactive tris-azide cross-linker for doped polymer interlayers and demonstrates its high efficiency and charge extraction capabilities in organic solar cells.

Findings

High cross-linking efficiency achieved

Excellent charge extraction properties demonstrated

Dopant diffusion at high doping levels reduces efficiency

Abstract

Solution-processable interlayers are an important building block 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 photo-reactive 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.