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Abstract Tin dioxide (SnO 2) is regarded as an effective electron transport material for attaining high-performance perovskite solar cells (PSCs). Herein, vertically aligned SnO 2 nanorod arrays are grown directly on fluorine-doped tin oxide (FTO) substrates in an acidic solution via hydrothermal method, where the area density of the nanorod arrays is tailored by varying the precursor concentration. Particularly, the mean diameters of the nanorods increase from 15 to 25 nm and the corresponding area densities decrease from 660 to 460 μm−2 with increasing the concentration of tin(IV) chloride pentahydrate. X-ray diffraction and X-ray photoelectron spectroscopy measurements reveal that the nanorod arrays are pure tetragonal rutile SnO 2 with a high degree of crystallinity. Mixed perovskites of (FAPbI 3) 0.85 (MAPbBr 3) 0.15 are infiltrated into these SnO 2 nanorod arrays, and the perovskite solar cells show an enhanced photovoltaic performance as compared to the nanoparticle counterpart. Perovskite solar cells based on SnO 2 nanorod arrays with the optimized area density exhibit the best power conversion efficiency of 15.46% which is attributed to an accelerated electron transport and a decreased recombination rate at SnO 2 /perovskite interface. Graphical abstract Image 1 Highlights • New approach is exploited for the synthesis of SnO 2 nanorod arrays. • The area density of the nanorod arrays could be tailored. • PSCs using SnO 2 nanorod arrays as ETL yield a high efficiency of 15.46%. • Interfacial charge transfer is systematically investigated. [ABSTRACT FROM AUTHOR]

Smooth and pin-hole free CoO films obtained from homogeneous colloidal solution are exploited as the hole transport layers of perovskite solar cells. Inorganic p-type materials show great potential as the hole transport layer in perovskite solar cells with the merits of low costs and enhanced chemical stability. As a p-type material, cobalt oxide (CoO) has received so far not that level of attention despite its high hole mobility. Herein, solution-processed p-type CoO nanocrystalline films are developed for inverted mixed perovskite solar cells. The ultrafine CoO nanocrystals are synthesized via an oil phase method, which are subsequently treated by a ligand exchange process using pyridine solvent to remove the long alkyl chains covering the nanocrystals. From this homogeneous colloidal solution CoO films are obtained, which exhibit a smooth and pin-hole free surface morphology with high transparency and good conductivity. The ultraviolet photoelectron spectrum also indicates that the energy levels of the CoO film match well with the mixed perovskite Cs 0.05 (FA 0.83 MA 0.17) 0.95 (I 0.83 Br 0.17) 3. Inverted solar cells based on crystalline CoO films with ligand exchange show a reasonable energy conversion efficiency, whereas devices based on CoO films without ligand exchange suffer from a strong S-shape JV-characteristic. Thus, the crystalline CoO films are foreseen to pave a new way of inorganic hole transport materials in the fields of perovskite solar cells. [ABSTRACT FROM AUTHOR]

2D Ag-ZIF interlayer plays a dual-passivation effect in terms of passivating both the oxygen vacancies on the SnO 2 and the uncoordinated Pb2+ at the bottom of the perovskite layer. [Display omitted] • 2D Ag-ZIFs are synthesized by a solvent modulated strategy. • 2D Ag-ZIF interlayer passivates the defects at perovskite/SnO 2 interface. • PSCs based on 2D Ag-ZIFs modified SnO 2 yield the champion PCE of 21.25%. • PSCs with 2D Ag-ZIFs exhibit enhanced UV and environmental stability. Despite the fact that perovskite solar cells (PSCs) have made rapid progress as a promising photovoltaic technology, defect management at the interface between the electron transport layer (ETL) and perovskite layer remains critical to significantly reduce energy loss of devices. Therefore, developing a robust and effective interlayer is imperative. Herein, 2D Ag doped ZIF-67 (Ag-ZIF) is designed by a solvent modulated strategy based on mixed N, N-dimethylformamide and ethanol, and further applied as an interfacial modifier in PSCs. Since the exposed dimethylimidazole ligands carried by Ag-ZIF and the metal ions, the oxygen vacancies on the SnO 2 surface and the uncoordinated Pb2+ and halogen ions at the bottom of the perovskite layer could be passivated effectively. Thus, suppressed non-radiative recombination and accelerated electron transport are achieved. Meanwhile, the robust framework and ultraviolet (UV)-resistant ability of Ag-ZIF could regulate the crystallization of perovskite film and prevent device from UV degradation. Consequently, the efficiency of PSC is remarkably boosted from 18.49% to 21.25% in accompany with enhanced UV and environmental stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Monodispersed SnO 2 microspheres assembled from tiny primary nanocrystallites with high specific surface area, excellent crystallinity and tunable building units demonstrate great potential in dye-sensitized/perovskite solar cells. Highlights • A novel approach is exploited for the synthesis of monodispersed SnO 2 microspheres. • The sizes of primary nanocrystals are tunable with adscititious water. • Dye-sensitized solar cells based on the microspheres yield an efficiency of 3.83%. • Perovskite solar cells based on the microspheres yield an efficiency of 15.41%. Abstract Mesoporous SnO 2 microspheres assembled from densely-packed nanocrystalline building units are a class of useful nanomaterials and have extensive optoelectronic applications, but so far it is still a challenge to acquire monodispersed microspheres. Here, monodispersed SnO 2 microspheres consisted of aggregated small primary nanocrystallites are synthesized via a surfactant-free solvothermal method. These SnO 2 microspheres have high specific surface area, excellent crystallinity and tunable building units. By precisely controlling the nucleation and growth, the obtained microspheres exhibit narrow size distribution, whose diameters are 200 ± 17 and 191 ± 16 nm from pure n-propanol and n-propanol/water mixed solvents, respectively. The sizes of primary nanocrystals slightly increase with the adscititious water. The SnO 2 microspheres exhibit large specific surface areas, leading to efficient sensitizer-loading in both dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). The sub-micron-sized microspheres could also enhance the light-harvesting of the solar cells due to their light-scattering capability. As the primary nanocrystal multiply contacts densely to neighbouring grains, such intergrowth would improve the electron transport through the grain boundaries. Eventually, a power conversion efficiency of 3.83% is yielded for pure SnO 2 -based DSSCs when the SnO 2 microspheres are used as the scattering layers, and an efficiency of 15.41% is obtained when they are used as the electron transport layers in PSCs. [ABSTRACT FROM AUTHOR]

The presence of heterogeneous interfacial defects limits the efficiency and long-term stability of the perovskite solar cells (PSCs). Rational passivation of interfacial defects and reduction of nonradiative recombination at the perovskite active layer are effective ways to achieve efficient PSCs. Here, a heterointerface engineering strategy is presented by employing a multifunctional molecule of reduced l -glutathione (GSH). The introduction of GSH improves the crystallization of SnO 2 , resulting in a continuous and conformal coverage of SnO 2 on the FTO surface. And the GSH buffer layer improves the affinity between SnO 2 and perovskite, resulting in the formation of large grains of perovskite. In addition, GSH bridges the perovskite to SnO 2 through multi-dentate ligands (-COOH, –NH 2 , –CONH–, –HS), which passivates the multiple defects at the heterogeneous interfaces while accelerates the electron transport. As a result, the PCE of the GSH-SnO 2 ETL based PSC significantly increases to 21.66% with no noticeable hysteresis. Meanwhile, compared with the control PSC, the unencapsulated GSH-SnO 2 based PSC exhibits better environmental stability, which maintains more than 80% of its initial PCE after 600 h of placement in atmospheric environment. GSH bridges the perovskite to SnO 2 through multi-dentate ligands, which passivates the multiple defects at the heterogeneous interfaces while accelerates the electron transport. [Display omitted] • GSH-SnO 2 has a contiguous and conformal coverage on the FTO substrate. • Multidentate ligands dually passivate various defects at the SnO 2 /perovskite heterogeneous interface. • An electron transport bridge is constructed between SnO 2 and perovskite layer. • The GSH-SnO 2 based PSCs achieve an enhanced PCE of 21.66%. [ABSTRACT FROM AUTHOR]

Perovskite solar cells based on thiourea-treated SnO 2 nanorod arrays exhibit a high power conversion efficiency of 20.18%. [Display omitted] • The micro-morphology of SnO 2 nanorod arrays is optimized to reduce the charge recombination. • Surface sulfuration passivates the interfacial defects at perovskite/ETL interface. • A record PCE of 20.18% is achieved for SnO 2 NRAs based PSCs. Vertically aligned one-dimensional nanorod arrays (NRAs) show great potential as electron transport layers (ETLs) for perovskite solar cells (PSCs) because of the unique characteristic which could realize the directional charge transport and enhanced charge collection. However, the severe charge recombination at the heterointerface between the NRAs ETL and perovskite layer often leads to the unsatisfactory power conversion efficiency (PCE). Here, we remarkably boost the performance of SnO 2 NRAs ETL through microstructural and surface chemical engineering. First, the longitudinal size of NRAs is adjusted to alleviate the charge accumulation at the heterointerface. Next, the surface affinity of SnO 2 NRAs is improved by thiourea sulfuration for a better penetration of perovskite precursor. More importantly, the strong interaction between the sulfur and the uncoordinated Pb2+ effectively passivate the buried interfacial defects of perovskite layer. Surface sulfuration reconstructs the gradient energy level and promotes the interfacial electron transfer between the ETL and the perovskite layer. As a result, a record PCE of 20.18 % is achieved for the S-SnO 2 NRAs based PSCs till now. Meanwhile, the operational stability of the device is enhanced especially in the near-ultraviolet region, which maintains above 80 % of the initial PCE after 72 h of continuous irradiation under ultraviolet light. [ABSTRACT FROM AUTHOR]

One-dimensional nanorod arrays show great potential as electron transport layers of perovskite solar cells due to their unique characteristic of oriented electron transport. Herein, anatase phase TiO 2 nanorod arrays are successfully grown on FTO conductive glass by a facile hydrothermal method using tetrabutyl titanate as precursor. By regulating the concentration of tetrabutyl titanate, TiO 2 nanorods with the length of 50, 200, 300 and 1000 nm are synthesized. XRD and Raman spectra show that the nanorods are pure anatase phase, while SEM and TEM images reveal that they are polycrystalline structure. The anatase TiO 2 nanorod array films have homogeneous surface morphologies, which are beneficial to deposit compact and pinhole-free perovskite films. The light absorption, photoluminescence quenching and trap densities of the films are systematically investigated. Consequently, the perovskite solar cells based on 50 nm anatase TiO 2 nanorod arrays show the best photoelectric conversion efficiency of 15.3%, and those based on 200, 300, 1000 nm nanorod arrays achieve the photoelectric conversion efficiencies of 14.5%, 13.8% and 12.1%, respectively. Perovskite solar cells based on anatase TiO 2 nanorod arrays exhibit a high power conversion efficiency of 15.3%. Image 1 • New approach for the synthesis of anatase phase TiO 2 nanorod arrays. • Anatase TiO 2 nanorod arrays with tunable length ranged from 50 to 1000 nm. • PSCs based on anatase TiO 2 nanorod arrays yield a high efficiency of 15.3%. [ABSTRACT FROM AUTHOR]

Mesoporous SnO 2 microspheres are a class of promising electron transport materials for mesoscopic perovskite solar cells, but a smooth and dense film as requested by electron transport layer is difficult to realize using the microspheres. Here, a series of monodispersed SnO 2 microspheres with high specific surface area and good crystallinity are synthesized via a surfactant-free solvothermal method. These SnO 2 microspheres showing small diameters of about 75, 110 and 200 nm with narrow size distribution are achieved by precisely controlling the crystal growth process. They are suitable for constructing the electron transport layers whose thickness is only about hundreds nanometers. Besides, as the microspheres easily slip off from the substrate during the conventional spin coating process, the spray coating method is exploited to prepare high quality electron transport layers. As a result, a power conversion efficiency of 16.85% is yielded by using the 75 nm sized SnO 2 microspheres as the electron transport layers. This high power conversion efficiency is attributed to the fast electron transport and inhibited charge recombination. To further improve the charge transfer between the electron transport layer and perovskite layer, graphene quantum dots are added into the SnO 2 microspheres, and a best efficiency of 17.08% is obtained. Image 1 • SnO 2 microspheres with small diameters of 75, 110 and 200 nm are synthesized. • High quality SnO 2 microsphere electron transport layers are prepared by spray coating. • A high efficiency of 17.08% is obtained for the mesoscopic perovskite solar cells. [ABSTRACT FROM AUTHOR]