This study focuses on the crucial problem of the stability of organic photovoltaic (OPV) devices, aiming to shed light on the photo and thermal degradation mechanisms during prolonged irradiation under ambient conditions. For this purpose, the stability enhancement of bulk heterojunction OPV devices upon embedding surfactant free Au nanoparticles (NPs) into the photoactive layer is investigated by in situ time-resolved energy dispersive X-ray reflectometry (EDXR), photoluminescence (PL) and Raman spectroscopy as well as device degradation electrical measurements. It is shown that besides the improved cell efficiency attributed to plasmon absorption and scattering effects, the embedded NPs act as performance stabilizers, giving rise to enhanced structural stability and, in turn, to reduced photodegradation rate of the respective OPV devices. It is particularly clarified that, in addition to further stabilization of the polymer–fullerene blend, the observed improvement can be ascribed to a NP-mediated mitigation of the photooxidation effect at the cathode–active layer interface. Our work suggests the exploitation of surfactant free NPs to be a successful approach to address aging effects in OPV devices.

We describe the synthesis and nonlinear absorption properties of triarylamine derivatives. Six molecules were synthesised by using a double Ullmann coupling procedure. UV-Vis absorption spectra show the excellent transparency of these triarylamine derivatives in the visible range (λ_cut-off ≤ 420 nm). Nonlinear absorption measurements show a broadband nonlinear absorption range extending between 450–650 nm with an optimised efficiency for a planar conjugated system (fluorene, molecule 10) or a hindered donor group (molecule 12). These data were interpreted by means of a two step three-photon absorption scheme: a TPA process followed by an S₁→S_n ESA step; the product of both spectra is qualitatively in good agreement with nonlinear absorption spectra, leading to different molecular engineering approaches for optimisation of these features in the visible range through TPA and/or ESA properties.