An Ultra-low Concentration of Gold Nanoparticles Embedded in the NiO Hole Transport Layer Boosts the Performance of p-i-n Perovskite Solar Cells

NiO_x is a promising hole transport material for p-i-n perovskite solar cells (PVSCs) on account of its high mobility, excellent stability and prospect for large-scale fabrication. However, the typical conductivity of NiO_x is low because of the low carrier concentration, which consequently compromises its photovoltaic performance. Herein, we show that the carrier concentration of NiO_x can be improved by as much as three times through embedding a small concentration (0.11 At%) of gold nanoparticles (Au-NPs), 2–3 nm in diameter, into the NiO_x thin film. The enhancement is due to the formation of Ohmic contact between Au and NiO_x while avoiding direct contact between Au and perovskite. All key parameters of the PVSC, namely J_sc, V_oc, and FF have improved, and the overall efficiency shows a significant improvement from 17.8% to 20.2%. The small size, low concentration, and Ohmic contact nature of the embedded Au-NPs, together with this simple method point to a new promising direction for developing high performance PVSCs.