Enhanced Stability of Aluminum Nanoparticle-Doped Organic Solar Cells

Enhancement of the stability of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices is reported by the addition of surfactant-free aluminum (Al) nanoparticles (NPs) into the photoactive layer. The universality of the effect is demonstrated for two different BHJ systems, namely, the well-studied poly­(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as well as the high efficient poly­[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]:[6,6]-phenyl-C71-butyric acid methyl ester (PCDTBT:PC₇₁BM). It is shown that the lifetime of the devices with Al NPs, operating under continuous one-sun illumination in ambient conditions, is more than three times longer compared to the reference devices. Using complementary analytical techniques for in situ studies, we have explored the underlying mechanisms behind the observed stability improvement in the case of the P3HT:PCBM system. In particular, laser-induced fluorescence (LIF), photoluminescence decay and Fourier transform infrared (FTIR) spectroscopy experiments were performed and complemented with device degradation electrical measurements. It is found that the embedded Al NPs act as performance stabilizers, giving rise to enhanced structural stability of the active blend. Furthermore, it is revealed that the observed improvement can also be ascribed to NP-mediated mitigation of the photo-oxidation effect. This study addresses a major issue in OPV devices, that is, photoinduced stability, indicating that the exploitation of Al NPs could be a successful approach toward fabricating OPVs exhibiting long-term operating lifetimes.