Low Temperature Fabrication for High Performance Flexible CsPbI2Br Perovskite Solar Cells.

All-inorganic CsPbX3-based perovskites, such as CsPbI2Br, show much better thermal and illumination stability than their organic-inorganic hybrid counterparts. However, fabrication of high-quality CsPbI2Br perovskite film normally requires annealing at a high temperature (>250 °C) that is not compatible with the plastic substrate. In this work, a Lewis base adduct-promoted growth process that makes it possible to fabricate high quality CsPbI2Br perovskite films at low temperature is promoted. The mechanism is attributed to synthesized dimethyl sulfoxide (DMSO) adducts which allow a low activation energy route to form CsPbI2Br perovskite films during the thermal annealing treatment. A power conversion efficiency (PCE) of 13.54% is achieved. As far as it is known, this is the highest efficiency for the CsPbI2Br solar cells fabricated at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI2Br PSCs with PCE as high as 11.73%. Surprisingly, the bare devices without any encapsulation maintain 70% of their original PCEs after being stored in ambient air for 700 h. This work provides an approach for preparing other high performance CsPbX3-based perovskite solar cells (PSCs) at low temperature, particularly for flexible ones.

Enhancing Efficiency and Stability of Perovskite Solar Cells through Nb-Doping of TiO2 at Low Temperature.

The conduction band energy, conductivity, mobility, and electronic trap states of electron transport layer (ETL) are very important to the efficiency and stability of a planar perovskite solar cell (PSC). However, as the most widely used ETL, TiO2 often needs to be prepared under high temperature and has unfavorable electrical properties such as low conductivity and high electronic trap states. Modifications such as elemental doping are effective methods for improving the electrical properties of TiO2 and the performance of PSCs. In this study, Nb-doped TiO2 films are prepared by a facile one-port chemical bath process at low temperature (70 °C) and applied as a high quality ETL for planar PSCs. Compared with pure TiO2, the Nb-doped TiO2 is more efficient for photogenerated electron injection and extraction, showing higher conductivity, higher mobility, and lower trap-state density. A PSC with 1% Nb-doped TiO2 yielded a power conversion efficiency of more than 19%, with about 90% of its initial efficiency remaining after storing for 1200 h in air or annealing at 80 °C for 20 h in a glovebox.

Strings of polymer microspheres stabilized by oxidized carbon nanotubes.

Oxidized carbon nanotubes (CNTOs) with hydrophilic oxygen-containing functional groups and hydrophobic conjugated structure are prepared by the oxidation of carbon nanotubes (CNTs). After the polymerization of styrene with CNTOs dispersed in aqueous phase, polystyrene (PS) microspheres with string-like structure are obtained. Thermogravimetic analysis (TGA), differential scanning calorimeter (DSC) and Raman results indicate the strong interaction between the separated PS chains from the oil phase and CNTOs during the initial stage of the polymerization. These adsorbed PS chains on the surface of CNTOs are quickly swollen by the monomer and they grow in size during the further polymerization. The pH value and the ion strength of aqueous phase obviously affect the stability of PS microspheres. The particle size of microspheres is also determined by the pH. We demonstrate that the one-dimensional structure of CNTOs is responsible for the formation of polymer microspheres with special architecture.

Preparation of graphene oxide coated polystyrene microspheres by Pickering emulsion polymerization.

Exfoliated graphene oxide (GO) nanosheets with hydrophilic oxygen-containing functional groups and hydrophobic residual conjugated structure are prepared by the oxidation of graphite powders. Polymerization of styrene stabilized by GO nanosheets is conducted at varied pH values. The morphology of the products is observed by field-emission scanning electron microscope (FE-SEM). It is found that GO coated polystyrene (PS) microspheres with narrow size distribution are obtained, although highly hydrophilic GO nanosheets cannot stabilize the monomer droplets in aqueous phase. Flocculation of polymer microspheres and GO nanosheets embedded in the PS matrix is induced by further decreasing the hydrophilicity of stabilizer. FT-IR, UV-vis spectra, XRD patterns and TGA results indicate the strong interaction between resulted PS chains and GO nanosheets during the initial stage of the polymerization. The amphiphilicity of GO nanosheets and the interaction between polymer and stabilizer are considered to be responsible for the fabrication of GO coated PS colloidal particles.

Slightly surface-functionalized polystyrene microspheres prepared via Pickering emulsion polymerization using for electrophoretic displays.

Slightly surface-functionalized polystyrene (PS) microspheres are prepared by photocatalytic Pickering emulsion polymerization using sodium styrene sulfonate (SSS)-modified titania hydrosol as a stabilizer. Aqueous electrophoresis measurements indicate the adsorption of bifunctional SSS anions on the surface of titania nanoparticles via electrostatic interaction. SSS molecules participate in the copolymerization with the monomers before the nucleation and thus have a great effect on the morphology and surface structure of the obtained PS microspheres. Appropriate SSS concentration leads to PS microspheres with small size, narrow distribution, and uniform surface chemistry. This kind of polymer particles can be used as a good candidate for the electrophoretic displays because of their high colloidal stability and electrophoretic mobility in the apolar solvent.