Two-dimensional (2D) nanomaterials have been the focus of substantial research interest recently owing to their fascinating and excellent properties. However, 2D porous materials have remained quite rare due to the difficulty of creating pores in 2D nanostructures. Here, we have synthesized a novel type of single-layered 2D mesoporous TiO nanosheets with very uniform size and thickness as well as ordered mesostructure from an unprecedented hydrothermal-induced solvent-confined assembly approach. The F127/TiO spherical monomicelles are first formed and redispersed in ethanol and glycerol, followed by a hydrothermal treatment to assemble these subunits into single-layered 2D mesostructure owing to the confinement effect of highly adhered glycerol solvent. The obtained 2D mesoporous TiO nanosheets have a relative mean size at around 500 × 500 nm and can be randomly stacked into a bulk. The TiO nanosheets possess only one layer of ordered mesopores with a pore size of 4.0 nm, a very high surface area of 210 m g and a uniform thickness of 5.5 nm. The thickness can be further manipulated from 5.5 to 27.6 nm via simply tuning precursor concentration or solvent ratio. Due to the well-defined 2D morphology and large mesoporosity as well as crystalline anatase mesopore walls, these uniform TiO nanosheets are capable of providing large accessible voids for sodium ion adsorption and intercalation as well as preventing volume expansion. As expected, these mesoporous TiO nanosheets have exhibited an excellent reversible capacity of 220 mAh g at 100 mA g as sodium-ion battery anodes, and they can retain at 199 mAh g after numerous cycles at different current densities. The capacity is retained at 44 mAh g even at a large current density of 10 A g after 10 000 cycles, demonstrating a remarkable performance for energy storage.

low exciton binding energy [ 20,21 ] and long carrier diffusion length, [21][22][23] metal halide perovskites with organic counterions have enabled both mesoscopic and planar solar cells to achieve power conversion effi ciencies (PCEs) >18%, [24][25][26][27][28][29] with state-of-theart mesocopic devices reaching a certifi ed PCE of 20.1%. [ 27 ] To date, perovskite solar cells with planar heterojunction structures are slightly less effi cient than their mesoscopic counterparts, but their fabrication is straightforward and compatible with well-established solution-based low temperature fabrication roll-to-roll procedures used for the production of polymer solar cells. [24][25][26][27] The incorporation of charge selective transport layers at the electrode/active layer junctions has often been regarded as a prerequisite to realize effi cient charge extraction in planar perovskite solar cells. [ 30 ] Thus, great effort has been focused on the development and understanding of interfacial engineering between perovskite and electron transport layers (ETLs) or hole transport layers (HTLs) for effective charge carrier separation. [31][32][33][34][35] In perovskite solar cells, the diffusion length of electrons is shorter than holes and it is regarded as a major limitation associated with these devices. [ 36,37 ] To address this limitation, compact semiconducting metal oxide (e.g., ZnO, TiO 2 ) ETLs have been used to facilitate electron transport in planar heterojunction devices. [ 2,14,38,39 ] In addition to the use of metal oxide layers, electrode work function modifi cation by an interlayer can further improve the performance of perovskite solar cells. [ 26,[40][41][42][43][44][45][46][47] For example, Yang et al. incorporated polyethyleneimine ethoxylated (PEIE) between indium tin oxide (ITO) electrode and TiO 2 to signifi cantly increase the PCE of planar heterojunction perovskite solar cells, identifying that reduction of ITO's work function (Φ) by PEIE, due to the presence of a negative interfacial dipole, was a leading contributor to the observed device performance improvement. [ 26 ] Phenyl-C 61 -butyric acid methyl ester (PC 61 BM) has been used as an alternative ETL to metal oxide layers in planar heterojunction devices, providing more effi cient charge injection from perovskite, [ 25 ] while allowing for low-temperature solution processing that precludes ITO's use as an electron-extracting electrode. [ 25,48,49 ] In addition, the deposition of PC 61 BM on perovskite fi lm [ 50 ] or making perovskite-PC 61 BM hybrid active layer [ 51 ] is effective to passivate charge trap states and defects Interface engineering is critical for achieving effi cient solar cells, yet a comprehensive understanding of the interface between a metal electrode and electron transport layer (ETL) is lacking. Here, a signifi cant power conversion effi ciency (PCE) improvement of fullerene/perovskite planar heterojunction solar cells from 7.5% to 15.5% is shown by inserting a fulleropyrrolidine interlayer between the silver electrode an...

Perovskite-containing tandem solar cells are attracting attention for their potential to achieve high efficiencies. We demonstrate a series connection of a ∼ 90 nm thick perovskite front subcell and a ∼ 100 nm thick polymer:fullerene blend back subcell that benefits from an efficient graded recombination layer containing a zwitterionic fullerene, silver (Ag), and molybdenum trioxide (MoO3). This methodology eliminates the adverse effects of thermal annealing or chemical treatment that occurs during perovskite fabrication on polymer-based front subcells. The record tandem perovskite/polymer solar cell efficiency of 16.0%, with low hysteresis, is 75% greater than that of the corresponding ∼ 90 nm thick perovskite single-junction device and 65% greater than that of the polymer single-junction device. The high efficiency of this hybrid tandem device, achieved using only a ∼ 90 nm thick perovskite layer, provides an opportunity to substantially reduce the lead content in the device, while maintaining the high performance derived from perovskites.

Three conjugated polymer zwitterions (CPZs), containing thiophene-, diketopyrrolopyrrole- (DPP), and naphthalene diimide (NDI) backbones, were synthesized with pendant zwitterions, specifically sulfobetaine groups. Diboronate-ester-functionalized bithiophene and benzothiadiazole monomers were copolymerized with zwitterion-substituted dibromothiophene, DPP, and NDI monomers by A2 + B2 Suzuki polymerization. The CPZs were incorporated into polymer solar cells (PSCs) as interlayers between the photoactive layer and Ag cathode. The thiophene-based CPZs gave power conversion efficiencies (PCEs) of about 5%, while the narrow-energy-gap DPP- and NDI-based CPZs performed exceptionally well, giving PCEs of 9.49% and 10.19%, respectively. The interlayer thickness had only a minor impact on the device performance for the DPP- and NDI-CPZs, a finding attributed to their electron-transport properties. Ultraviolet photoelectron and reflectance spectroscopies, combined with external quantum efficiency measurements, provided structure-property relationships that lend insight into the function of CPZ interlayers in PSCs. NDI-based CPZ interlayers provide some of the best performing organic solar cells reported to date, and prove useful in conjunction with high-performing polymer-active layers and stable, high-work-function, metal cathodes.