Spatial mapping of photocurrents in organic solar cells comprising wedge-shaped absorber layers for an efficient material screening

• Published in: Solar energy materials and solar cells 2012-09, Vol.104, p.18-22
• Main Authors: Nickel, Felix, Sprau, Christian, Klein, Michael F.G., Kapetana, Panagiota, Christ, Nico, Liu, Xin, Klinkhammer, Soenke, Lemmer, Uli, Colsmann, Alexander
• Format: Article
• Language: English
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; Functional layer thickness; Horizontal dipping; Natural energy; Organic electronics; Photoelectric conversion; Photovoltaic conversion; Polymer solar cell; Solar cells. Photoelectrochemical cells; Solar energy; Solution processing
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2012.04.026

In this work we present a facile route to an efficient experimental screening of new materials and to a layer thickness optimization in solution processable polymer photovoltaic devices. Therefore, we developed a method of fabricating solar cells with wedge-shaped active layers. Spatially resolved measurements of the solar cell short circuit current densities for different light absorbing polymers under white light allow for a quick conclusion about the optimum active layer thickness within the device. To demonstrate the generality of this experimental approach we studied the well-established photoactive blends from poly-(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PC61BM) or poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] and [6,6]-phenyl C71-butyric acid methyl ester (PCDTBT:PC71BM). The short circuit current densities are in very good agreement with optoelectronic device simulations and results from sample-by-sample measurements. ► New material- and time-efficient method for photocurrent optimization in organic photovoltaic devices. ► Method for material screening on very low quantities using wedge-shaped active layers. ► Exact pre-calculation of the wedge-shaped layer thickness from fluid dynamics. ► JSC dependency on the active layer thickness for P3HT:PC61BM and PCDTBT:PC71BM solar cells with a resolution below 10nm. ► n- and k-values of PCDTBT measured with spectroscopic ellipsometry.