One-step integration of a multiple-morphology gold nanoparticle array on a TiO₂ film: Via a facile sonochemical method for highly efficient organic photovoltaics

Integrating multiple-morphology plasmonic metal nanostructures into organic photovoltaics (OPVs) is highly desirable to enhance the efficiency of solar energy conversion because of their broadband plasmonic absorption. However, it remains challenging to develop facile fabrication methods that enable plasmonic metal nanoparticle (NP) arrays with multiple morphologies, a low degree of aggregation, and large-scale production. Herein, we report a one-step integration of well-dispersed and size-tunable multiple-morphology gold (Au) NP arrays on titanium dioxide (TiO₂) thin films via a facile sonochemical route. The multiple-morphology Au NP arrays are successfully employed to enhance the photovoltaic performance of bulk heterojunction OPVs. The multiple-morphology Au NPs exhibited a broad absorption band, which resulted in a large overlap with the absorption band of the OPV active layer, thus enhancing light absorption as well as photovoltaic performance. The average power conversion efficiencies (PCEs) of the devices with Au NP arrays were remarkably enhanced by up to 20.5%: from 3.42% to 4.12% for a P3HT:PC₆₁BM active layer, and the best device showed a PCE of 4.25%. For the high-efficiency PTB7:PC₇₁BM blend system, the average PCE was enhanced by up to 14.5%, from 7.46% to 8.54%, and the best device showed a PCE of 8.68%. The PCE enhancement mainly arose from the increased light absorption, which was caused by the strong surface plasmon resonance effects of the Au NP arrays. These results clearly demonstrated that such a multiple-morphology Au NPs array integrated on TiO₂ thin films can serve as a promising plasmonic component to raise OPV performance. This approach could be easily extended to other types of solar cells and other mainstream light-conversion systems used in photocatalysis and solar water splitting, and organic light-emitting diodes.