Research On Bowl-Shaped Superstructures Of CdSe Nanocrystals With Narrow-Sized Distribution And Their Photoelectric Properties

As one of the most well-known II-VI semiconductor nanocrystals, cadmium selenide?CdSe? has become the “model” nanocrystal system and been the hotspot of much basic research on the photoelectric properties of nanocrystals, owing to the accessible of high-quality and stable samples. CdSe nanocrystals have been found mainly in two crystalline forms: wurtzite and sphalerite. CdSe has bandgap of ? 1.797 eV in the wurtzite crystal phase and ? 1.712 e V in the zine blende phase.Most device applications based on nanocrystals require the control of size and size distribution of colloidal nanocrystals. The nanocrystals with narrow-sized distribution show narrow bandwidth of absorption and emission peaks. These nanocrystals may improve the performance of the photoelectric devices.However, due to the finite size of nanocrystals, the realization of the commercial application of nanocrystals is almost impossible. In order to overcome the shortcomings and realize a wide range of application, an alternative way is the self-assembly of inorganic nanocrystals into large and ordered superstructures and subsequent integration into functional devices via current manufacture techniques. It is considered a possible route that the micro materials prepared in mesoscopic and macroscopic devices.In this paper, the approach used cadmium stearate?Cd?SA?₂? as the Cd source and surface ligands, elemental selenium as Se compounds and 1-Octadecene?1-ODE? as the reaction medium to synthesize the CdSe nanocrystals with narrow-sized distribution. Via acutely temperature decrease, bowl-shaped CdSe superstructures were fabricated. In order to investigate the formation mechanism of bowl-shaped superstructures, the cooling rate of the solution was changed and the products were studied. The study showed that the formation of bowl-shaped CdSe superstructures was attributed to the high cooling rate and the decrease in the solubility of nanocrystals. With the rapid decrease of temperature, the solubility of the CdSe nanocrystals with narrow-sized distribution decreased, then a mass of small nanocrystals rapidly dissolved out of the solution and quickly assembled into superstructures. Some internal substances were surrounded by the nanocrystals and after the purification and centrifugation of the product, especially drying them before the characterization, the internal substances push the nanocrystals aside, thus producing bowl-shaped superstructures.Moreover, organic-inorganic hybrid photoswitch based on CdSe superstructures and poly?3-hexylthiophene??P3HT? were fabricated. The tests showed that the CdSe superstructures prepared in organic phase could be homogeneously mixed with P3 HT, which was benefit to effective separation of excitons and rapid transfer of carriers. The device gave an on/off switching ratio of ¹00 and showed the outstanding stability. Particularly, there was no obvious degradation observed upon cycling. The excellent photo-responsible performance illustrates that the superstructures hold great promise for the application of photoelectric devices.