Enhancing Stability of Perovskite Solar Cells to Moisture by the Facile Hydrophobic Passivation

In this study, a novel and facile passivation process for a perovskite solar cell is reported. Poor stability in ambient atmosphere, which is the most critical demerit of a perovskite solar cell, is overcome by a simple passivation process using a hydrophobic polymer layer. Teflon, the hydrophobic polymer, is deposited on the top of a perovskite solar cell by a spin-coating method. With the hydrophobic passivation, the perovskite solar cell shows negligible degradation after a 30 day storage in ambient atmosphere. Suppressed degradation of the perovskite film is proved in various ways: X-ray diffraction, light absorption spectrum, and quartz crystal microbalance. This simple but effective passivation process suggests new kind of approach to enhance stability of perovskite solar cells to moisture

Unbiased Sunlight-Driven Artificial Photosynthesis of Carbon Monoxide from CO₂ Using a ZnTe-Based Photocathode and a Perovskite Solar Cell in Tandem

Solar fuel production, mimicking natural photosynthesis of converting CO₂ into useful fuels and storing solar energy as chemical energy, has received great attention in recent years. Practical large-scale fuel production needs a unique device capable of CO₂ reduction using only solar energy and water as an electron source. Here we report such a system composed of a gold-decorated triple-layered ZnO@ZnTe@CdTe core–shell nanorod array photocathode and a CH₃NH₃PbI₃ perovskite solar cell in tandem. The assembly allows effective light harvesting of higher energy photons (>2.14 eV) from the front-side photocathode and lower energy photons (>1.5 eV) from the back-side-positioned perovskite solar cell in a single-photon excitation. This system represents an example of a photocathode–photovoltaic tandem device operating under sunlight without external bias for selective CO₂ conversion. It exhibited a steady solar-to-CO conversion efficiency over 0.35% and a solar-to-fuel conversion efficiency exceeding 0.43% including H₂ as a minor product

Solution-Processed Ultrathin TiO₂ Compact Layer Hybridized with Mesoporous TiO₂ for High-Performance Perovskite Solar Cells

The electron transport layer (ETL) is a key component of perovskite solar cells (PSCs) and must provide efficient electron extraction and collection while minimizing the charge recombination at interfaces in order to ensure high performance. Conventional bilayered TiO₂ ETLs fabricated by depositing compact TiO₂ (c-TiO₂) and mesoporous TiO₂ (mp-TiO₂) in sequence exhibit resistive losses due to the contact resistance at the c-TiO₂/mp-TiO₂ interface and the series resistance arising from the intrinsically low conductivity of TiO₂. Herein, to minimize such resistive losses, we developed a novel ETL consisting of an ultrathin c-TiO₂ layer hybridized with mp-TiO₂, which is fabricated by performing one-step spin-coating of a mp-TiO₂ solution containing a small amount of titanium diisopropoxide bis­(acetylacetonate) (TAA). By using electron microscopies and elemental mapping analysis, we establish that the optimal concentration of TAA produces an ultrathin blocking layer with a thickness of ∼3 nm and ensures that the mp-TiO₂ layer has a suitable porosity for efficient perovskite infiltration. We compare PSCs based on mesoscopic ETLs with and without compact layers to determine the role of the hole-blocking layer in their performances. The hybrid ETLs exhibit enhanced electron extraction and reduced charge recombination, resulting in better photovoltaic performances and reduced hysteresis of PSCs compared to those with conventional bilayered ETLs

Soft-Template Simple Synthesis of Ordered Mesoporous Titanium Nitride-Carbon Nanocomposite for High Performance Dye-Sensitized Solar Cell Counter Electrodes

Ordered mesoporous titanium nitride-carbon (denoted as OM TiN-C) nanocomposite with high surface area (389 m² g^–1) and uniform hexagonal mesopores (ca. 5.5 nm) was facilely synthesized via the soft-template method. As a structure-directing agent, Pluronic F127 triblock copolymer formed an ordered structure with inorganic precursors, resol polymer, and prehydrolyzed TiCl₄, followed by a successive heating at 700 °C under nitrogen and ammonia flow. In this study, the amorphous carbon within the parent OM TiO₂-C acted as a rigid support, preventing structural collapse during the conversion process of TiO₂ nanocrystals to TiN nanocrystals. The OM TiN-C was then successfully applied as counter electrode material in dye-sensitized solar cells (DSCs). The organic electrolyte disulfide/thiolate (T₂/T^–) was introduced to study the electrocatalytic property of the OM TiN-C nanocomposite. Because of the existence of TiN nanocrystals and the defect sites of the amorphous carbon, the DSCs using OM TiN-C as a counter electrode showed 6.71% energy conversion efficiency (platinum counter electrode DSCs: 3.32%) in the organic electrolyte system (T₂/T^–). Furthermore, the OM TiN-C counter electrode based DSCs showed an energy conversion efficiency of 8.41%, whereas the DSCs using platinum as a counter electrode showed a conversion efficiency of only 8.0% in an iodide electrolyte system. The superior performance of OM TiN-C counter electrode resulted from the low charge transfer resistance, enhanced electrical conductivity, and abundance of active sites of the OM TiN-C nanocomposite. Moreover, OM TiN-C counter electrode showed better chemical stability in organic electrolyte compared with the platinum counter electrode