Electroabsorption studies of organic p-i-n solar cells: Increase of the built-in voltage by higher doping concentration in the hole transport layer

Journal article

The built-in voltage in solar cells has a significant influence on the extraction of photogenerated charge carriers. For small molecule organic solar cells based on the p-i-n structure, we investigate the dependence of the built-in voltage on the work function of both the hole transport layer and the electrode material. The model system investigated here consists of a planar heterojunction with N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (MeO-TPD) as donor and Buckminster Fullerene (C₆₀) as acceptor material. A higher concentration of the dopant C₆₀F₃₆ in the hole transport layer induces a shift of the work function towards the transport level. The resulting increase of the built-in voltage is studied using electroabsorption spectroscopy, measuring the change in absorption (Stark effect) caused by an externally applied electric field. An evaluation of these electroabsorption spectra as a function of the applied DC voltage enables the direct measurement of the built-in voltage. It is also shown that an increased built-in voltage does lead to a larger short-circuit current as well as a larger fill factor. © 2013 Elsevier B.V. All rights reserved.

Authors: Siebert-Henze, E; Lyssenko, V; Fischer, J; Tietze, M; Brueckner, R

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Organic Electronics: physics, materials, applications
• Volume: 15
• Issue: 2
• Pages: 563-568
• Publication date: 2014-02-01
• DOI: 10.1016/j.orgel.2013.12.009
• ISSN: 1566-1199
• Language: English
• Keywords: Organic solar cells; Small molecules; Built-in voltage; Electroabsorption spectroscopy; Molecular doping