How do gold nanoparticles boost the performance of perovskite solar cells?

To achieve large-scale commercialization of perovskite thin-film solar cells in the near future, improving perovskite thin-films quality and properties is becoming more and more critical. We focus here on the effect of introducing gold nanoparticles (Au_NPs) in MAPbI3 layers for solar cells. Experimentally, we show a 12% improvement of the stabilized efficiency by introducing an optimized amount of Au_NPs. The nanoparticles action has been addressed through a combination of experiments and optical simulations. First, we have calculated Mie absorption coefficients, done numerical FDTD simulations and transfer-matrix simulations to model the localized surface plasmon resonance (LSPR) and light scattering efficiency of Au_NPs. They have allowed us to state that, to reach a significant beneficial effect, the nanoparticle volume ratio must be above 1%, which is far above the content in our optimized perovskite solar cells layers. Only a negligible enhancement of light absorption can be attributed to the Au_NPs. Secondly, by combining several analysis techniques, especially by using glow discharge-optical emission spectroscopy (GD-OES), we reveal the mechanism of how Au_NPs improve the quality of perovskite films. The gold nanoparticles lead to the formation of monolithic grains with few defects and reduced grain boundaries which are the targeted properties for high efficiency. Therefore, in our devices, the effect of Au_NPs on the improvement of the quality of the perovskite layer is far more significant than that of the increase in light-harvesting. Finally, further performance and stability increases have been achieved by introducing the treatment of Au_NPs/MAPbI3 film surface by n-propylammonium iodide (PAI). It resulted in a power conversion efficiency of over 20%.