Tetraaryldiamine-based electron-transporting interlayers for performance and stability enhancement of organic solar cells

Abstract

Three novel tetraaryldiamines are synthesized and applied as an interlayer between zinc oxide (ZnO) and photoactive layers in PTB7-Th:PC71BM solar cells. The arylamines have an optical bandgap of 3.0–3.4 eV and do not interfere with the light-harvesting window of our polymer:fullerene combination. They enhance the power conversion efficiency from 7.48% in the control device to 8.95%, 8.18%, and 7.84% in PN-, PA-, and PAP-based devices, respectively. The dependence of photovoltaic parameters on the deposition conditions of the interlayer reveals that the current density and fill factor are the main parameters that increase when tetraaryldiamines are used as an interlayer. The external quantum efficiency increases from 73.1% in the bare ZnO device to 77.7–82.0% in the interlayer-incorporated devices. The power loss owing to the series and shunt resistances is reduced by a suitable alignment of the electronic energy levels with the interlayer and enhanced charge transfer through the components. Interlayer-incorporated devices also show a superior environmental stability compared to devices using bare ZnO. The results of this study should help advance the engineering strategies for organic solar cells with enhanced performances.