Highly efficient planar heterojunction (PHJ) perovskite solar cells (PSCs) with a structure of ITO/ PEDOT:PSS/CH 3 NH 3 PbI 3 /PCBM/Al were fabricated by a low-temperature solution process. As employed silica-coated gold (Au@SiO 2 ) nanorods at the interface between the hole transport layer PEDOT:PSS and the active layer CH 3 NH 3 PbI 3 , the average power conversion efficiency (PCE) showed over 40% enhancement, of which the average PCE was improved from 10.9% for PHJ-PSCs without Au@SiO 2 to 15.6% for PHJ-PSCs with Au@SiO 2 , and the champion one up to 17.6% was achieved. Both experiment and simulation results proved that prominent efficiency enhancement comes from the localized surface plasmon resonance of Au@SiO 2 nanorods which could improve the incident light trapping as well as improve the transport and collection of charge carrier, resulting in the enhancement in device parameters. The results suggest that metal nanorods, e.g., Au@SiO 2 , could be employed to fabricate highefficiency and low-cost PHJ-PSCs.

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Moisture-assisted post-annealing was performed on carbon-electrode based planar perovskite solar cells so as to improve the hole-extraction process. It was observed that, after being annealed at a relative humidity of 30% for 2 h, the short-circuit current density, fill factor, and open circuit voltage were all improved, leading to an improvement of 21.75% of power conversion efficiency [from 10.53 (±0.98)% to 12.82 (±1.07)%, with the optimized one at 14.77% for reverse scanning]. The transient photovoltage/photocurrent decay measurement and impedance spectroscopy study showed that, after being annealed at a relative humidity of 30%, the charge extraction rate was accelerated and charge transfer resistance was reduced, while recombination between photo-generated charges was retarded. Scanning electron microscopy studies indicated that voids were reduced between the perovskite film and the carbon electrode, which was ascribed to the re-coarsening process of the perovskite during the post-annealing process as revealed by the X-ray diffraction study. The improved contact accelerated hole-extraction between the perovskite film and the carbon electrode and then upgraded device performance.