Dr. Ryan Crisp
My name is Ryan Crisp. I joined the Optoelectronic Materials group in October 2015 as a PostDoc researcher. I’m from the lovely state of Colorado (USA) where I did my BS, MSc, and PhD in Engineering (BS) and Applied Physics (MSc and PhD) at the Colorado School of Mines. My PhD research was conducted at the National Renewable Energy Laboratory (NREL) where I focused on the synthesis optoelectronic properties of quantum dots (QDs) and how they function in solar cells. Here at TU Delft, I am continuing many of the same activities but focus more on less toxic materials and spectroscopy of nanomaterials.
Specifically, I am developing a synthetic method to make InSb QDs. InSb has interesting optoelectronic properties where the electron effective mass is low and mobility is high meaning a process known as multiple exciton generation (where one photon can lead to the excitation of many electrons and holes depending on the photon energy) could be more efficient than in other materials. I am also comparing these results to more “traditional” materials like PbSe QDs shown in the transmission electron microscopy (TEM) image below and PbS QDs shown below that.
Alternatively, the main QD material used to make QD solar cells is PbS but seeing as Pb is a carcinogen we seek to replace it with something less toxic, for instance Ag2S is an interesting candidate. Work on synthesizing and screening the suitability of Ag2S QDs for solar is beginning. On a similar vein, I’m using another less toxic material, InP QDs, to make exploratory devices and test their feasibility in making lower cost, solution-processed solar cells.
Finally, there are few materials that emit efficiently in the NIR spectral region. I’m developing materials to improve the photoluminescence quantum yield (PLQY) at 800nm. Using many of the materials I’ve described above, I am optimizing and exploring different conditions’ effects on the PLQY. For instance growing a shell around PbS QDs leads to a shift in the absorption and emission spectrum and an increase in the PLQY as shown in the figure below.