Preparation of NaYF4:Tm, Yb, and Gd Luminescent Nanorods/SiO2 Nanospheres Composite Thin Film and Its Application in Perovskite Solar Cells.

In this study, we aim to minimize light loss and achieve high power conversion efficiencies (PCE) in perovskite solar cells (PSCs) by employing a spectral conversion film component with antireflection properties. In our scheme, NaYF4:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films are applied on CH3NH3PbI3 PSCs to improve the device efficiency. The film was fabricated by spin coating an aged silica sol containing NaYF4:Tm, Yb, and Gd luminescent nanorods. The size and the spectral conversion properties of the NaYF4:Tm, Yb, and Gd luminescent nanorods were controlled by tuning the Gd3+ ion concentration. The microstructure and the transmittance properties of the thin film were controlled by changing the concentration of NaYF4:Tm, Yb, and Gd luminescent nanorod in silica sol. The thin films have excellent spectral conversion properties while exhibiting a maximum transmittance. The photovoltaic performance of PSCs with NaYF4:Tm, Yb, and Gd luminescent nanorod/silica nanosphere-based thin films was systematically investigated. The light transmittance was optimized to 95.1% on a cleaned glass substrate, which resulted in an average increase of about 3.0% across the broadband range of 400-800 nm. The optimized films widen the spectrum of light absorbed by conventional PSC cells and reduce reflections across a broad range, enhancing the photovoltaic performance of PSCs. As a result, the PCE of the PSC increased from 14.51% for the reference device without a thin film to 15.67% for the PSC device with an optimized thin film. This study presents a comprehensive solution to the problem of Fresnel reflection and spectral response mismatch of the PSCs, which provides new ideas for the light management of PSCs.

High performance perovskite solar cells using Cu9S5 supraparticles incorporated hole transport layers.

We disclose novel photovoltaic device physics and present details of device mechanisms by investigating perovskite solar cells (PSCs) incorporating Cu9S5@SiO2 supraparticles (SUPs) into Spiro-OMeTAD based hole transport layers (HTLs). High quality colloidal Cu9S5 nanocrystals (NCs) were prepared using a hot-injection approach. Multiple Cu9S5 NCs were further embedded in silica to construct a Cu9S5@SiO2 SUP. Cu9S5@SiO2 SUPs were blended into Spiro-OMeTAD based HTLs with different weight ratios. Theoretical and experimental results show that the very strong light scattering or reflecting properties of Cu9S5@SiO2 SUPs blended in the PSC device in a proper proportion distribute to increase the light energy trapped within the device, leading to significant enhancement of light absorption in the active layer. Additionally, the incorporated Cu9S5@SiO2 SUPs can also promote the electrical conductivity and hole-transport capacity of the HTL. Significantly larger conductivity and higher hole injection efficiency were demonstrated in the HTM with the optimal weight ratios of Cu9S5@SiO2 SUPs. As a result, efficient Cu9S5 SUPs based PSC devices were obtained with average power conversion efficiency (PCE) of 18.21% at an optimal weight ratio of Cu9S5 SUPs. Compared with PSC solar cells without Cu9S5@SiO2 SUPs (of which the average PCE is 14.38%), a remarkable enhancement over 26% in average PCE was achieved. This study provides an innovative approach to efficiently promote the performance of PSC devices by employing optically stable, low-cost and green p-type semiconductor SUPs.

Enhancing Upconversion from NaYF4:Yb,Er@NaYF4 Core-Shell Nanoparticles Assembled on Metallic Nanostructures.

We report a simple method for the fabrication of a three-layered plasmonic structure of silicon substrate-Au nanospheres-upconversion particles (UCNPs) that displays up to 101-fold fluorescence enhancement. Monodispersed pure hexagonal-phase NaYF4:Yb,Er core and NaYF4:Yb,Er@NaYF4 core@shell nanocrystals were prepared by a solvothermal method. Two dimensional (2D) assembled Au spheres were prepared on a Si substrate, and then, 2D arrays of UCNPs were deposited on the grown 2D monolayered Au spheres by a self-organizing process. The distance between plasmonic Au NPs and rare-earth (RE) core was finely adjusted by changing the undoped NaYF4 shell thickness. The UC emission enhancement shows a pronounced shell thickness dependence. For the non-plasmonic structured samples, a single peak in upconversion luminescence (UCL) enhancement was observed as the undoped NaYF4 shell thickness increases from 0 nm to 23.0 nm. In contrast, for the plasmonic structured samples, multi-oscillations in UCL enhancement were observed in the undoped NaYF4 shell thickness range of 0-23.0 nm, where the UCL enhancement factors of three bands (521 nm, 540 nm and 654 nm) are high up to 65, 101 and 61, respectively, at 19.6 nm-thick NaYF4 shell. The multi-oscillations in UCL enhancement in the plasmonic samples can be associated with plasmonic coupling between arrays of core-shell UCNPs with various sizes and the underlying 2D Au spheres. The related mechanisms of the UCL enhancements are discussed.

Plasmonic Effects of Metallic Nanoparticles on Enhancing Performance of Perovskite Solar Cells.

We report systematic design and formation of plasmonic perovskite solar cells (PSCs) by integrating Au@TiO2 core-shell nanoparticles (NPs) into porous TiO2 and/or perovskite semiconductor capping layers. The plasmonic effects in the formed PSCs are examined. The most efficient configuration is obtained by incorporating Au@TiO2 NPs into both the porous TiO2 and the perovskite capping layers, which increases the power conversion efficiency (PCE) from 12.59% to 18.24%, demonstrating over 44% enhancement, compared with the reference device without the metal NPs. The PCE enhancement is mainly attributed to short-circuit current improvement. The plasmonic enhancement effects of Au@TiO2 core-shell nanosphere photovoltaic composites are explored based on the combination of UV-vis absorption spectroscopy, external quantum efficiency (EQE), photocurrent properties, and photoluminescence (PL). The addition of Au@TiO2 nanospheres increased the rate of exciton generation and the probability of exciton dissociation, enhancing charge separation/transfer, reducing the recombination rate, and facilitating carrier transport in the device. This study contributes to understanding of plasmonic effects in perovskite solar cells and also provides a promising approach for simultaneous photon energy and electron management.