1wileyonlinelibrary.com nanomaterial's size, surface area, and light-scattering ability.Recently, multi-shell hollow nanoparticles (MS-HNPs) have been highlighted as promising materials for DSSC applications, offering a high surface area and strong light scattering. MS-HNPs, composed of inner and outer shells, have a benefi cial confi guration for multirefl ection (of sunlight) and redox reactions with the electrolyte. Moreover, the surface area of MS-HNPs is much larger than that of single-shell (SS)-HNPs having the same size. Various MS-HNPs have been developed, such as multilayerd SnO 2 hollow microspheres coated to TiO 2 , [ 17 ] quintuple-shelled SnO 2 hollow microspheres, [ 18 ] multi-shelled ZnO hollow microspheres, [ 19 ] and shell-in-shell TiO 2 hollow microspheres. [ 20 ] These MS-HNPs improve the power conversion effi ciency of the DSSCs, due to their strong lightscattering effect and increased surface area. However, among the MS-HNPs, the largest surface area of multi-shelled ZnO hollow microspheres was only 47 m 2 g −1 , which is not suffi cient for light absorption in the sensitizer layer. [ 19 ] Additionally, most MS-HNPs are synthesized using a hydrothermal process, which limits the mass production of MS-HNPs. In particular, TiO 2 , commonly used as the working electrode in DSSCs, has several fabrication issues, including diffi culty in controlling the morphology, size, and aggregation, due to the fast reaction rate of the TiO 2 precursor. [ 21,22 ] Therefore, the development of MS-HNPs with nano-scale size, high surface area, and strong light-scattering remains a challenge.Herein, we introduce a fabrication method for nano-sized MS-TiO 2 -HNPs using a sol-gel method, combined with calcination and etching processes. The MS-TiO 2 -HNPs used in this study were composed of three shells: a small inner shell (diameter: 50 nm), a middle shell (diameter: 100 nm), and an outer shell (diameter: 160 nm). The fabricated MS-TiO 2 -HNPs were expected to be multifunctional, due to their large surface area of 171 m 2 g −1 , multi-refl ection capability, and enhanced electrolyte diffusion. Specifi cally, the smallest inner shell of the MS-TiO 2 -HNPs provided a high surface area. Additionally, the multi-shell structure induced multirefl ection for solar devices. We observed an increase in the power conversion effi ciency for the MS-TiO 2 -HNP-DSSCs of 17.5% (from 8.0% for SS-TiO 2 -HNP-DSSCs to 9.4% for MS-TiO 2 -HNP-DSSCs). To our knowledge, this is the fi rst report of nano-sized MS-TiO 2 -HNPs with a high surface area. Multi-Shell Porous TiO 2 Hollow Nanoparticles for Enhanced Light Harvesting in

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-CHNHPbI (MAPbI) 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.

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 (V ) 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.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has now exceeded 20%; thus, research focus has shifted to establishing the foundations for commercialization. One of the pivotal themes is to curtail the overall fabrication time, to reduce unit cost, and mass-produce PSCs. Additionally, energy dissipation during the thermal annealing (TA) stage must be minimized by realizing a genuine low-temperature (LT) process. Here, tin oxide (SnO ) thin films (TFs) are formulated at extremely high speed, within 5 min, under an almost room-temperature environment (<50 °C), using atmospheric Ar/O plasma energy (P-SnO ) and are applied as an electron transport layer of a "n-i-p"-type planar PSC. Compared with a thermally annealed SnO TF (T-SnO ), the P-SnO TF yields a more even surface but also outstanding electrical conductivity with higher electron mobility and a lower number of charge trap sites, consequently achieving a superior PCE of 19.56% in P-SnO -based PSCs. These findings motivate the use of a plasma strategy to fabricate various metal oxide TFs using the sol-gel route.