Room-Temperature Solvent Evaporation Induced Crystallization: A General Strategy for Growth of Halide Perovskite Single Crystals by Applying the Le Chatelier's Principle.

The growth of high-quality halide perovskite single crystals is imperative to study their intrinsic physical properties and to realize high-performance optoelectronic devices. Here, a room-temperature solvent evaporation-induced crystallization (RTSEIC) method is reported based on Le Chatelier's principle, which provides a general strategy to grow halide perovskite single crystals including 3D, 2D, 1D, and 0D, and either hybrid or all-inorganic halide perovskites. Taking 2D n-BA2 PbBr4 (n-BA = butylammonium) as an example, the room-temperature crystallization kinetics is demonstrated. The centimeter-sized n-BA2 PbBr4 single crystals exhibit an extremely small full width at half maximum (FWHM) of 0.024° in (0 0 2) plane rocking curve and a small trap density of 2.74 × 1010 cm-3 . The superior crystalline quality endows the n-BA2 PbBr4 single crystal ultraviolet photodetectors with recorded performance among reported n-BA2 PbBr4 ultraviolet photodetectors, demonstrating a detectivity reaching 1.8 × 1013 Jones, a fast response time of 55 µs and a high on-off ratio of 104 . The low-cost, simple, general, and efficient RTSEIC method is anticipated to promote the blossoming of halide perovskites single crystals.

Incorporation of Nanostructured Carbon Composite Materials into Counter Electrodes for Highly Efficient Dye-Sensitized Solar Cells.

Dye-sensitized solar cells (DSSCs) composed of nanostructured carbon composite materials-stacked counter electrodes (CEs) were fabricated in the present study. As the potential replacement of expensive platinum (Pt) thin film, various carbon composite materials, including zero-dimensional carbon nanoparticles (CNPs), one-dimensional multiwalled carbon nanotubes (MWCNTs), and two-dimensional graphene flakes (GFs) as a suitable charge transfer medium were deposited on the surface of CEs using a screen printing process. As the results, CNPs were found to result in deteriorating the charge transfer from CE to liquid electrolyte due to the formation of highly aggregated structures with very low specific surface area. However, MWCNTs and MWCNTs-added carbon composites (e.g., CNP/MWCNT, MWCNT/GF, CNP/MWCNT/GF) were found to enhance the charge transfer from CE to liquid electrolyte due to the formation of highly networked structures with high specific surface area. The resulting PCE of DSSCs composed of pure MWCNTs- and MWCNTs-added carbon composites-based CEs were very similar with that of DSSCs composed of Pt-based CEs. This suggests that the nanostructured carbon materials especially composed of MWCNTs and their composites are one of the promising candidates to replace the expensive Pt in the CEs of DSSCs.