Haejun Yu

Hexagonal β-NaYF4:Yb3+, Er3+ Nanoprism-Incorporated Upconverting Layer in Perovskite Solar Cells for Near-Infrared Sunlight Harvesting

Hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms, successfully prepared using a hydrothermal method, were incorporated into CH3NH3PbI3 perovskite solar cells (PSCs) as an upconverting mesoporous layer. Due to their near-infrared (NIR) sunlight harvesting, the PSCs based on the upconverting mesoporous layer exhibited a power conversion efficiency of 16.0%, an increase of 13.7% compared with conventional TiO2 nanoparticle-based PSCs (14.1%). This result suggests that the hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms expand the absorption range of the PSC via upconversion photoluminescence, leading to an enhancement of the photocurrent.

SiO2/TiO2 based hollow nanostructures as scaffold layers and Al-doping in the electron transfer layer for efficient perovskite solar cells

Perovskite solar cells (PSCs) have been developed intensively recently due to their excellent efficiency. In this study, PSCs were fabricated using a hollow structure as a scaffold layer and Al doped TiO2 (Al-TiO2) as a compact layer. The hollow structure showed effective loading of perovskite (CH3NH3PbI3Cl3−x) on the working electrode of the PSCs. In particular, using SiO2/TiO2 hollow nanoparticles (STHNPs) instead of TiO2 hollow nanoparticles (THNPs) as insulators improved the open circuit voltage, because STHNPs did not allow photogenerated electrons to transfer easily from the perovskite. Al-TiO2 compact layers synthesized using a low temperature procedure (≤150 °C) promoted electron extraction and reduced the recombination, leading to enhanced power conversion efficiency (PCE). An optimum PCE of 14.7% was achieved for PSCs based on STHNP scaffold layers with Al doping in the electron transfer layer.

Large Grain-Based Hole-Blocking Layer-Free Planar-Type Perovskite Solar Cell with Best Efficiency of 18.20%

There remains tremendous interest in perovskite solar cells (PSCs) in the solar energy field; the certified power conversion efficiency (PCE) now exceeds 20%. Along with research focused on enhancing PCE, studies are also underway concerning PSC commercialization. It is crucial to simplify the fabrication process and reduce the production cost to facilitate commercialization. Herein, we successfully fabricated highly efficient hole-blocking layer (HBL)-free PSCs through vigorously interrupting penetration of hole-transport material (HTM) into fluorine-doped tin oxide by a large grain based-CH3NH3PbI3 (MAPbI3) film, thereby obtaining a PCE of 18.20%. Our results advance the commercialization of PSCs via a simple fabrication system and a low-cost approach in respect of mass production and recyclability.

Synergistic effects of three-dimensional orchid-like TiO2 nanowire networks and plasmonic nanoparticles for highly efficient mesoscopic perovskite solar cells

TiO2 nanoparticle (TiO2 NP)-based mesoscopic electron transport structures have been frequently used in organic–inorganic hybrid perovskite solar cells (PSCs) for rapid electron transport. However, TiO2 NPs that are densely agglomerated in the scaffold layer may inhibit the penetration of a perovskite solution thereby deteriorating the device performance. Here, we use three-dimensional orchid-like TiO2 nanowires (OC-TiO2 NWs) as scaffold materials to overcome the deficiencies of TiO2 NP-based structures. The perovskite precursor deeply infiltrated into the spacious pores within the OC-TiO2 NW network and crystallized in the scaffold layer, which increased the recombination resistance and charge extraction efficiency. Additionally, Ag NPs were introduced in the form of a silica-coated Ag@OC-TiO2 NW (SiO2@Ag@OC-TiO2 NW) composite to achieve still better performance through localized surface plasmon resonance (LSPR) and exciton dissociation inducement of the Ag NPs. Consequently, a PSC based on this collaborative scaffold consisting of Ag NPs and OC-TiO2 NWs exhibited a high power conversion efficiency (PCE) of 15.09%, which is an improvement of 24% over a PSC based on a TiO2 NP scaffold layer, where the average PCE was 12.17%.

Paintable Carbon-Based Perovskite Solar Cells with Engineered Perovskite/Carbon Interface Using Carbon Nanotubes Dripping Method

Paintable carbon electrode-based perovskite solar cells (PSCs) are of particular interest due to their material and fabrication process costs, as well as their moisture stability. However, printing the carbon paste on the perovskite layer limits the quality of the interface between the perovskite layer and carbon electrode. Herein, an attempt to enhance the performance of the paintable carbon-based PSCs is made using a modified solvent dripping method that involves dripping of the carbon nanotubes (CNTs), which is dispersed in chlorobenzene solution. This method allows CNTs to penetrate into both the perovskite film and carbon electrode, facilitating fast hole transport between the two layers. Furthermore, this method is results in increased open circuit voltage (Voc ) and fill factor (FF), providing better contact at the perovskite/carbon interfaces. The best devices made with CNT dripping show 13.57% power conversion efficiency and hysteresis-free performance.

Highly efficient perovskite solar cells incorporating NiO nanotubes: increased grain size and enhanced charge extraction

Perovskite solar cells (PSCs) have greatly improved through optimizing the morphology and charge extraction of the perovskite film. To increase the efficiency, we have developed a new method of adding NiO nanotubes (NTs) to the perovskite precursor solution. The NiO NTs promoted the growth of perovskite grains during annealing and facilitated charge extraction. The increase in the grain size improved the crystallinity of the perovskite film and reduced the grain boundaries that could trap charge. Additionally, the NiO NTs located between the grain boundaries transferred holes, which prevented charge recombination. The efficiency of the PSCs increased due to the improved crystallinity and charge extraction of the perovskite film. Devices incorporating the NiO NTs exhibited power conversion efficiencies of 19.3 and 12.82% for planar-type and carbon-based PSCs, respectively.

Size effects of a graphene quantum dot modified-blocking TiO2 layer for efficient planar perovskite solar cells

Research on the addition of suitable materials into perovskite solar cells (PSCs) for improved performance is as important as the fabrication of efficient perovskite films themselves. An attempt to enhance the performance of planar-type perovskite solar cells was performed by introducing graphene quantum dots (GQDs) onto a blocking TiO2 layer via O2 plasma treatment. Furthermore, the bandgap of the GQDs was tuned through their size control and the effects of the GQD size on cell performance were explored. The GQDs can induce fast electron extraction and the formation of the improved perovskite quality. The devices with appropriately sized-GQDs showed an average of 10% enhancement compared with those of cells without GQDs and achieved 19.11% as the best power conversion efficiency (PCE). Furthermore, GQDs contributed to the reduction in the extent of current–voltage hysteresis, which was attributed to the planar structure.

Fabrication of Uniform Wrinkled Silica Nanoparticles and Their Application to Abrasives in Chemical Mechanical Planarization

A simple one-pot method is reported for the fabrication of uniform wrinkled silica nanoparticles (WSNs). Rapid cooling of reactants at the appropriate moment during synthesis allowed the separation of nucleation and growth stages, resulting in uniform particles. The factors affecting particle size and interwrinkle distance were also investigated. WSNs with particle sizes of 65-400 nm, interwrinkle distances of 10-33 nm, and surface areas up to 617 m2 g-1 were fabricated. Furthermore, our results demonstrate the advantages of WSNs over comparable nonporous silica nanospheres and fumed silica-based products as an abrasive material in chemical mechanical planarization processes.

Fabrication of monodisperse nitrogen-doped carbon double-shell hollow nanoparticles for supercapacitors

Nitrogen-doped carbon double-shell nanoparticles (NC DS-HNPs) were fabricated using SiO2/TiO2 double-shell nanoparticles (ST DS-HNPs) and polydopamine-coating. The NC DS-HNPs have a high surface area of 873.52 m2 g−1 and a pore volume of 2.86 cm3 g−1, which are favorable characteristics for supercapacitors. In addition, nitrogen doping induced pseudo-capacitance via the redox activity of the surface functionalities. A specific capacitance of 202 F g−1 was achieved for supercapacitors based on NC DS-HNPs at a current density of 0.5 A g−1. Consequently, the unique morphology and electrochemical properties of NC DS-HNPs show great potential for future energy-related devices.

Efficient and moisture-resistant hole transport layer for inverted perovskite solar cells using solution-processed polyaniline

Inverted-structure perovskite solar cells (PSCs), with low-temperature processed poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and perovskite-passivating phenyl–C61–butyric acid methyl ester (PCBM) employed as charge transport layers, have great potential as efficient, flexible, and hysteresis-free solar cells. However, PEDOT:PSS processed from an aqueous solution has a hygroscopic nature, and can degrade the ambient stability of moisture-vulnerable perovskite electronics. Furthermore, excess insulating PSS in the PEDOT:PSS complex can deteriorate the hole extraction and photovoltaic performance of the solar cell. In this work, polyaniline doped with camphorsulfonic acid (PANI-CSA) is introduced as a hole transport layer (HTL) to promote hole extraction ability and improve the efficiency and stability of inverted PSCs. The device fabricated with PANI-CSA exhibited superior photovoltaic performance, with a maximum efficiency of 15.42%, compared to 14.11% efficiency for the device fabricated with PEDOT:PSS. Most notably, the stability of the device fabricated with PANI-CSA was greatly improved due to a stable HTL/perovskite interface against exposure to ambient moisture.