Optoelectronic characterization of printed organic solar cells

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For non-fullerene acceptor (NFA)-based organic solar cells, highest efficiencies are reported with spin-coated photoactive layers, from halogenated solvent with ca. 100 nm thick active layers. Such layers were shown to exhibit a well-defined intermolecular nanostructure and low energetic disorder. The situation may largely change when printing thicker active layers from non-chlorinated solvents. In this proposal, we will link energetic disorder to the photovoltaic parameters by providing detailed analysis between properties of printed devices formed from benign solvents and those of spin-coated state-of-the-art solar cells. Thicker active layers printed from non-halogenated solvents are anticipated to have different miscibility, interfacial interaction and morphology thereby energetic disorder. To this end in the project we will employ transient absorption, time-delayed collection field and photocurrent-photoinduced absorption to study, free charge generation and recombination as a function of field and temperature. On the other hand, space limited charge current measurements will be used to quantify energetic disorder and mobility of printed devices. The results will enter detailed device simulation together with groups of the consortium. Our investigations will start with selected material combinations for which high efficiencies are already reported on spin-coated devices and continue with single component active layers to be developed in course of this Research Unit, which will also from the focus of the second funding period.