Hole Transport Materials for Tin-Based Perovskite Solar Cells: Properties, Progress, Prospects.

The power conversion efficiency of modern perovskite solar cells has surpassed that of commercial photovoltaic technology, showing great potential for commercial applications. However, the current high-performance perovskite solar cells all contain toxic lead elements, blocking their progress toward industrialization. Lead-free tin-based perovskite solar cells have attracted tremendous research interest, and more than 14% power conversion efficiency has been achieved. In tin-based perovskite, Sn2+ is easily oxidized to Sn4+ in air. During this process, two additional electrons are introduced to form a heavy p-type doping perovskite layer, necessitating the production of hole transport materials different from that of lead-based perovskite devices or organic solar cells. In this review, for the first time, we summarize the hole transport materials used in the development of tin-based perovskite solar cells, describe the impact of different hole transport materials on the performance of tin-based perovskite solar cell devices, and summarize the recent progress of hole transport materials. Lastly, the development direction of lead-free tin-based perovskite devices in terms of hole transport materials is discussed based on their current development status. This comprehensive review contributes to the development of efficient, stable, and environmentally friendly tin-based perovskite devices and provides guidance for the hole transport layer material design.

UV-O3 treated annealing-free cerium oxide as electron transport layers in flexible planar perovskite solar cells.

Fabricating electron transport layers at low temperatures is challenging but highly desired in the field of flexible perovskite solar cells (f-PSCs). In this study, highly uniform cerium oxide (CeO x ) films prepared by the UV-O3 treatment have been successfully applied as the electron transport layer (ETL) in methylammonium lead halide (CH3NH3PbI3) perovskite-based f-PSCs. Under AM 1.5 G sunlight with 100 mW cm-2, these cells exhibited an open-circuit voltage (V oc) of 0.98 V, a short-circuit current density (J sc) of 19.42 mA cm-2, a fill factor (FF) of 0.72 and power conversion efficiency (PCE) of 14.63%. The PCE was much higher than that of the control planar CeO x ETL (PCE ∼ 9.08%) prepared at a low temperature (80 °C) without the UV-O3 treatment, and this was ascribed to the improved CeO x film, enhanced light absorption and suppressed charge recombination. The cells that bend at 15 mm of radius showed excellent stability with less than 10% reduction in PCE after 500 cycles of repeated bending at ambient temperature. The charge-transmission kinetic parameters and long-term stability of the CeO x -based f-PSCs were analyzed as well.

Metal-organic frameworks at interfaces of hybrid perovskite solar cells for enhanced photovoltaic properties.

In this study, metal-organic frameworks, as an interfacial layer, were introduced into perovskite solar cells (PSCs) for the first time. An interface modified with the metal-organic framework ZIF-8 efficiently enhanced perovskite crystallinity and grain sizes, and the photovoltaic performance of the PSCs was significantly improved, resulting in a maximum PCE of 16.99%.

Highly Efficient Perovskite Solar Cells Based on Zn2 Ti3 O8 Nanoparticles as Electron Transport Material.

Developing ternary metal oxides as electron transport layers (ETLs) for perovskite solar cells is a great challenge in the field of third-generation photovoltaics. In this study, a highly mesoporous Zn2 Ti3 O8 (m-ZTO) scaffold is synthesized by ion-exchange method and used as ETL for the fabrication of methyl ammonium lead halide (CH3 NH3 PbI3 ) perovskite solar cells. The optimized devices exhibit 17.21 % power conversion efficiency (PCE) with an open circuit voltage (Voc ) of 1.02 V, short-circuit current density (Jsc ) of 21.97 mA cm-2 and fill factor (FF) of 0.77 under AM 1.5G sunlight (100 mW cm-2 ). The PCE is significantly higher than that based on mesoporous ST01 (m-ST01; 10 nm TiO2 powder) layer (η=14.93 %), which is ascribed to the deeper conductive band of ZTO nanoparticles, better light absorption and smaller charge recombination. The devices stored for 100 days at ambient temperature with humidity of 10 % showed excellent stability with only 12 % reduction of the PCE. The charge transmission kinetic and long-term stability parameters of the ZTO-based perovskite film growth are discussed as well.

Incorporating Zn2SnO4 quantum dots and aggregates for enhanced performance in dye-sensitized ZnO solar cells.

The performance of dye-sensitized ZnO solar cells was improved by a facile surface-treatment approach through chemical-bath deposition. After the surface treatment, the quantum dots of Zn(2)SnO(4) were deposited onto ZnO nanoparticles accompanied by the aggregations of Zn(2)SnO(4) nanoparticles. The ZnO film displayed a better resistance to acidic dye solution on account of the deposited Zn(2)SnO(4) nanoparticles. Meanwhile, the open-circuit photovoltage was greatly enhanced, which can be ascribed to the increased conduction-band edge of ZnO and inhibited interfacial charge recombination. Although the deposition of Zn(2)SnO(4) decreased the adsorption amounts of N719 dye, the aggregates of Zn(2)SnO(4) with a size of 350-450 nm acted as the effective light-scattering layer, thereby resulting in an improved short-circuit photocurrent. By co-sensitizing 10 µm-thick ZnO film with N719 and D131 dyes, a top efficiency of 4.38% was achieved under the illumination of one sun (AM 1.5, 100 mW cm(-2)).

Photocatalytic bactericidal mechanism of nanoscale TiO2 films on Escherichia coli.

Two kinds of nanoscale TiO2 films were prepared by magnetron sputtering and screen printing methods, respectively. Results show that both phase composition and specific surface area of the film affect the photocatalytic bactericidal efficiency. Time-series in situ atomic force microscopy (AFM) observation were further used to characterize the cellular responses of Escherichia coli (E. coli) in photocatalytic process. Some nanosized patches were found on the bacterial surface in the forepart of photocatalytic reaction. It suggested that the photocatalytic attack induced the self-protection of bacteria at first. Subsequently, some cracks on the surface and the enlargement of cell body indicated that the cell wall was damaged and lost its structure supporting function, and it eventually led to the death of bacteria.

Significant reduction of harmful compounds in tobacco smoke by the use of titanate nanosheets and nanotubes.

Titanate nanosheets and nanotubes have first been introduced into cigarette filter, a great range of harmful compounds including tar, nicotine, ammonia, hydrogen cyanide, selected carbonyls and phenolic compounds can be reduced efficiently.